an39511
Member
Delete
Last edited:
Bcd536hp external speaker connection considerations and precautions
- Thread starter Mike_G_D
- Start date
- Status
pkneeyahx
Human
I've discovered that, as previously mentioned, pass the combined and dc blocked audio through a isolating transformer removes the high pitched buzz.
Sorry I haven't replied earlier, I've been dealing with a lot of personal stuff.
Anyway, to address some questions and concerns noted here:
My background is in analog and RF hardware engineering (test, primarily and some development) so my knowledge and advice are based on logical technical principles which are, in turn, based on the information available in this website and elsewhere. UPMAN has stated that the audio external speaker output was a BTL based design and gave one abbreviated caution concerning not connecting the external speaker jack ring to ground. Extrapolating from this and based on what many users are seeing and experiencing when attempting to connect their scanners to PC's, etc., I simply developed my more involved and detailed outline of the issue as a convenient "one stop shopping" point for users to find - especially since I saw so many separate threads concerning these problems.
As to how my suggestions may affect the warranty - as far as I know, none of what I suggested should void the warranty in any way since you are not opening up the radio's case and making any modifications. All of what I suggested can be done externally with no internal modifications to the scanner.
As to the USB connection degrading the performance as one user has reported - I can only guess that since the USB port contains a DC ground, somehow, depending on how that user has made the external audio connection to the external device it is causing some form of ground loop with that device relative to the external speaker audio. I would suggest the use of an audio isolation transformer as in the first solution I outlined as that would fully isolate any ground issues between the scanner and the audio device being fed (in theory, anyway - not knowing the exact setup I cannot be absolutely sure). Otherwise, in lieu of the transformer approach, I would make doubly sure that there is only one connection to the tip or ring of the external speaker jack and NOT both between the 536 external speaker jack and the device being fed. I would also make sure there is no other physical connection to said device except the USB cable. If the problem still persists, then I can only guess that there is something in the design of the device's audio input circuit that creates a low impedance to ground relative to the external speaker output of the 536 which, when the USB cable is connected between the devices, does cause problems. Not knowing any details, I cannot say whether this has the potential to cause any permanent damage or not.
As to the high pitched "buzz" someone mentioned - again, I can only speculate. It sounds like it may be a similar problem as the above. It all depends on how the external device is designed in terms of its audio input circuitry. PC soundcards do have varying designs and can be associated with a lot of noise sources that may not be issues under most circumstances but may manifest themselves under special circumstances. Apparently, according to the last post, it was solved via using BOTH an isolation transformer AND inline DC blocking which seems a redundant approach in theory because the transformer alone will block any DC. However, since it appears to work then we can only call it an effective solution! Have you tried the transformer alone without any capacitor inline and is the buzz still there; in other words, you found you need BOTH an inline series cap AND an isolation transformer after the 536 external speaker output? The transformer alone should, in theory, yield complete isolation; however, some isolation transformers might be made in such a way as to provide a high impedance path to ground on one side that may cause issues depending on which way you are using it - try always to make the primary side the one connected to the 536 external speaker jack and, if you have an ohmmeter, check for any path to ground from the two transformer leads.
Having brought up the ohmmeter - if you have access to one and know how to use it properly, it's probably a good idea to check for low impedances to ground (say less than several thousand ohms) on whatever connection you are using to connect between the 536 and the device being fed. Ideally, there should be no low impedance path between the 536 external speaker jack, tip or ring, and chassis ground of either the 536 itself or the device being fed - isolating the connecting cable/circuit from both the 536 and the device being fed and then checking to make sure there is no low impedance ground path on the 536 side of the connection before usage is a good test to make!
-Mike
Anyway, to address some questions and concerns noted here:
My background is in analog and RF hardware engineering (test, primarily and some development) so my knowledge and advice are based on logical technical principles which are, in turn, based on the information available in this website and elsewhere. UPMAN has stated that the audio external speaker output was a BTL based design and gave one abbreviated caution concerning not connecting the external speaker jack ring to ground. Extrapolating from this and based on what many users are seeing and experiencing when attempting to connect their scanners to PC's, etc., I simply developed my more involved and detailed outline of the issue as a convenient "one stop shopping" point for users to find - especially since I saw so many separate threads concerning these problems.
As to how my suggestions may affect the warranty - as far as I know, none of what I suggested should void the warranty in any way since you are not opening up the radio's case and making any modifications. All of what I suggested can be done externally with no internal modifications to the scanner.
As to the USB connection degrading the performance as one user has reported - I can only guess that since the USB port contains a DC ground, somehow, depending on how that user has made the external audio connection to the external device it is causing some form of ground loop with that device relative to the external speaker audio. I would suggest the use of an audio isolation transformer as in the first solution I outlined as that would fully isolate any ground issues between the scanner and the audio device being fed (in theory, anyway - not knowing the exact setup I cannot be absolutely sure). Otherwise, in lieu of the transformer approach, I would make doubly sure that there is only one connection to the tip or ring of the external speaker jack and NOT both between the 536 external speaker jack and the device being fed. I would also make sure there is no other physical connection to said device except the USB cable. If the problem still persists, then I can only guess that there is something in the design of the device's audio input circuit that creates a low impedance to ground relative to the external speaker output of the 536 which, when the USB cable is connected between the devices, does cause problems. Not knowing any details, I cannot say whether this has the potential to cause any permanent damage or not.
As to the high pitched "buzz" someone mentioned - again, I can only speculate. It sounds like it may be a similar problem as the above. It all depends on how the external device is designed in terms of its audio input circuitry. PC soundcards do have varying designs and can be associated with a lot of noise sources that may not be issues under most circumstances but may manifest themselves under special circumstances. Apparently, according to the last post, it was solved via using BOTH an isolation transformer AND inline DC blocking which seems a redundant approach in theory because the transformer alone will block any DC. However, since it appears to work then we can only call it an effective solution! Have you tried the transformer alone without any capacitor inline and is the buzz still there; in other words, you found you need BOTH an inline series cap AND an isolation transformer after the 536 external speaker output? The transformer alone should, in theory, yield complete isolation; however, some isolation transformers might be made in such a way as to provide a high impedance path to ground on one side that may cause issues depending on which way you are using it - try always to make the primary side the one connected to the 536 external speaker jack and, if you have an ohmmeter, check for any path to ground from the two transformer leads.
Having brought up the ohmmeter - if you have access to one and know how to use it properly, it's probably a good idea to check for low impedances to ground (say less than several thousand ohms) on whatever connection you are using to connect between the 536 and the device being fed. Ideally, there should be no low impedance path between the 536 external speaker jack, tip or ring, and chassis ground of either the 536 itself or the device being fed - isolating the connecting cable/circuit from both the 536 and the device being fed and then checking to make sure there is no low impedance ground path on the 536 side of the connection before usage is a good test to make!
-Mike
an39511
Member
Mike_G_D: I want to thank you for all you have done and taking the time helping to explain and provide suggestions. I have made my cable and it works perfectly. I chose to skip the isolation transformer because I had all the parts to make the direct connection. Using the capacitor took care of the DC and the resister takes care of the possibility of over-driving the PC input.
I have attached a png file of a simple schematic for a passive audio tap for the 536 external speaker output. This will allow one to use both an external passive speaker as well as simultaneously connecting to a PC MIC or LINE input. The potentiometer allows one to adjust the level of the input to the PC without grossly affecting the speaker level. The potentiometer could be either linear or audio taper as it is not really a "volume" level per se, more it is a fine level adjustment for keeping the audio into the PC within acceptable limits (below distortion level); basically it gives one an extra layer of PC audio level adjustment in addition to the soundcard software controls. Due to the very high level of speaker output from the 536, this is a desirable feature.
The resistors and potentiometer need only be in the 1/4 watt range but anything higher would be fine. The values are not critical. I suggest the pot be no less than 10K. The cap provides DC isolation protecting the radio (and circuit) from any DC "phantom power" that might be present on the PC audio mic input.
To use, you first set the audio of the radio as desired for comfortable sound from the external speaker. Then, you would adjust the circuit pot for the best quality audio into the PC (you could monitor with headphones connected to the PC and monitor the input). I would set the PC software level input adjustment to about midway and then adjust the circuit potentiometer; you may have to go back and forth with that (software adjust and circuit pot adjust) to get best results.
I have not built and tested this circuit but it is quite simple and should work. I would suggest that someone with the means and some technical understanding try it out and give any feedback for changes or modifications on this thread. If you are not technically proficient and/or are at all timid about using it then I would suggest waiting until someone who has the means and knowledge has tried it and worked out all of the fine details and construction details before building and using one yourself.
I made many notes on the schematic that should make it clear how careful one needs to be in NOT connecting either the tip or ring of the external speaker jack to ground! Please DO NOT IGNORE THESE NOTES!
-Mike
The resistors and potentiometer need only be in the 1/4 watt range but anything higher would be fine. The values are not critical. I suggest the pot be no less than 10K. The cap provides DC isolation protecting the radio (and circuit) from any DC "phantom power" that might be present on the PC audio mic input.
To use, you first set the audio of the radio as desired for comfortable sound from the external speaker. Then, you would adjust the circuit pot for the best quality audio into the PC (you could monitor with headphones connected to the PC and monitor the input). I would set the PC software level input adjustment to about midway and then adjust the circuit potentiometer; you may have to go back and forth with that (software adjust and circuit pot adjust) to get best results.
I have not built and tested this circuit but it is quite simple and should work. I would suggest that someone with the means and some technical understanding try it out and give any feedback for changes or modifications on this thread. If you are not technically proficient and/or are at all timid about using it then I would suggest waiting until someone who has the means and knowledge has tried it and worked out all of the fine details and construction details before building and using one yourself.
I made many notes on the schematic that should make it clear how careful one needs to be in NOT connecting either the tip or ring of the external speaker jack to ground! Please DO NOT IGNORE THESE NOTES!
-Mike
Attachments
Last edited:
Mike G D
Thank you for your detailed explanation of what is going on with the external speaker. I may do what an39511 did for now. That being said, I don't think most people who pay $600 for this scanner (I bought two) expect to have to go through this process to be able to use line-in feeds. I suspect, like others, that this issue will be handled by the new Siren application when it is available, but I wish Uniden (I realize Paul is under certain constraints), so what I mean is Uniden as a corporation, would just come out and tell us what they have planned.
If the new Siren application takes care of this, great, wonderful, tell us that is what is planned, and I am sure everyone will patiently wait. That is the least we can expect for this 536HP scanner which everyone waited for almost 3 months.
That said, it is a great scanner, and I think once everything get worked out, including the Wi-Fi app and advanced features, the bar is going to be very high for anyone else to come close to, let alone beat as far as scanners go in this price range.
Steve AA6IO
Thank you for your detailed explanation of what is going on with the external speaker. I may do what an39511 did for now. That being said, I don't think most people who pay $600 for this scanner (I bought two) expect to have to go through this process to be able to use line-in feeds. I suspect, like others, that this issue will be handled by the new Siren application when it is available, but I wish Uniden (I realize Paul is under certain constraints), so what I mean is Uniden as a corporation, would just come out and tell us what they have planned.
If the new Siren application takes care of this, great, wonderful, tell us that is what is planned, and I am sure everyone will patiently wait. That is the least we can expect for this 536HP scanner which everyone waited for almost 3 months.
That said, it is a great scanner, and I think once everything get worked out, including the Wi-Fi app and advanced features, the bar is going to be very high for anyone else to come close to, let alone beat as far as scanners go in this price range.
Steve AA6IO
Amen! That is exactly what I have been saying too. I wish Uniden would just tell us if this is going to be IP based streaming. That would resolve so many issues in regards to streaming and there would be no need to connect the scanner to the sound card at all. I would suggest people wait to find out what this app and scanner has in store instead of venturing out making cables to connect to your PC and possibly causing damage.
I would be surprised if Uniden did not plan on using the USB port for audio data for PC input; as you've said, and I believe this likely, they (Uniden) most likely are working on firmware and/or software support to allow this and the hardware is likely designed accordingly.
That having been said, because so many were already trying to connect their PC audio input to the scanner and running into the problems using the BTL external speaker output, I thought it best to try to clarify the issues and then give a simple circuit for actual use to do this in the interim.
The circuit I described should not cause any damage to the BTL amp as it isolates ground by a pretty high resistance. The pot value can be increased to pretty much any value you have available and the same goes for the value of R1; what you want is the full value of R1 plus R2 (the pot) to be roughly a minimum of 20K and more is fine. At full level into a relatively low impedance mic input (say, 200 ohms or so) would present the most "risk" but the value of R1 protects against that. At the opposite extreme, at lowest level, the value is approximately the full value of the pot plus the value of R1 so with the presented values that is 30K between the BTL tip line and ground which should be fine. Again, these values can be increased if desired for extra "protection" and the circuit should still work ok.
As you've said, once the digital audio link is up and running, using the external speaker jack for connection to a PC is negated for the most part. But you never know when a need may come up in the future for whatever reason and it is always best to be informed and prepared just in case.
-Mike
That having been said, because so many were already trying to connect their PC audio input to the scanner and running into the problems using the BTL external speaker output, I thought it best to try to clarify the issues and then give a simple circuit for actual use to do this in the interim.
The circuit I described should not cause any damage to the BTL amp as it isolates ground by a pretty high resistance. The pot value can be increased to pretty much any value you have available and the same goes for the value of R1; what you want is the full value of R1 plus R2 (the pot) to be roughly a minimum of 20K and more is fine. At full level into a relatively low impedance mic input (say, 200 ohms or so) would present the most "risk" but the value of R1 protects against that. At the opposite extreme, at lowest level, the value is approximately the full value of the pot plus the value of R1 so with the presented values that is 30K between the BTL tip line and ground which should be fine. Again, these values can be increased if desired for extra "protection" and the circuit should still work ok.
As you've said, once the digital audio link is up and running, using the external speaker jack for connection to a PC is negated for the most part. But you never know when a need may come up in the future for whatever reason and it is always best to be informed and prepared just in case.
-Mike
JamesO
Member
A possible plug and play solution?
Telco & Multimedia Ground Isolation Transformer - 3.5mm M/F - Computer Cable Store™
Telco & Multimedia Ground Isolation Transformer - 3.5mm M/F - Computer Cable Store™
- Joined
- Aug 1, 2011
- Messages
- 893
It appears to be Mono so it should work with the speaker out as it is mono too.
Yes, as far as I can tell, from that description it should work. It's designed for "600 ohms" but I assume it is basically a 1:1 transformer.
If you want to use it with an external speaker simultaneously, I would suggest using a Y adapter attached to the 536 external speaker jack with one lead going to the speaker and the other to this adapter. Then plug a male-to-male mono cable into the female out of the transformer and the other end into the PC audio input. Your sole audio leveling would be using the PC audio input level controls in the software mixer.
As far as I can see, that should work ok with one possible issue - the mic or line input of the PC might be loaded down due to the reflected low output impedance of the 536's audio output amp (and speaker if used) through the transformer. I don't think this will be a problem but it might be; if so (say the audio is really low and/or distorted and cannot be compensated for using the PC mixer level controls) then you might need to add a series resistor in line to the PC input (tip, center conductor). I'd say anything around 1K or so should be fine.
-Mike
JamesO
Member
I am just trying to toss out some pre-made options for some folks.
The problem is I assume many people may use the systems very differently.
User #1 may want to connect the audio for streaming, but not really care about listening to the scanner. User #1 may be able to listen the scanner via the sound card input and use the computer to listen.
User #2 may want to connect the audio for streaming, but wants to listen to the scanner audio full time or some times. The the issue is User #2 cannot use the scanner volume to modify or change the speaker level. In this case a separate amplified speaker might be needed in this case.
User #3 may wan to connect the audio to a mixer for steaming or patching into a sound system of some sort.
There are probably user #4-#X??
This is why I tossed out the idea for Uniden to come up with some form of solution that is blessed by them and works. Yes the user community can come up with a solution, but why should we have to.
Hopefully Uniden will learn from this issue and put back a fixed line level output in future scanners.
I am guessing that the line level output was removed because of the built in recording capability and Uniden assumed that nobody would want or need a line level output, however, this is does not appear too be the situation.
Again, I plan on interfacing a Motorola HSN1006A to both my 996XT and the 536HP. I have these currently connected in just a passive mode as an external speaker, however, I expect that there may be some issues when I go to connect the Motorola speaker up in amplified mode with the common ground.
The problem is I assume many people may use the systems very differently.
User #1 may want to connect the audio for streaming, but not really care about listening to the scanner. User #1 may be able to listen the scanner via the sound card input and use the computer to listen.
User #2 may want to connect the audio for streaming, but wants to listen to the scanner audio full time or some times. The the issue is User #2 cannot use the scanner volume to modify or change the speaker level. In this case a separate amplified speaker might be needed in this case.
User #3 may wan to connect the audio to a mixer for steaming or patching into a sound system of some sort.
There are probably user #4-#X??
This is why I tossed out the idea for Uniden to come up with some form of solution that is blessed by them and works. Yes the user community can come up with a solution, but why should we have to.
Hopefully Uniden will learn from this issue and put back a fixed line level output in future scanners.
I am guessing that the line level output was removed because of the built in recording capability and Uniden assumed that nobody would want or need a line level output, however, this is does not appear too be the situation.
Again, I plan on interfacing a Motorola HSN1006A to both my 996XT and the 536HP. I have these currently connected in just a passive mode as an external speaker, however, I expect that there may be some issues when I go to connect the Motorola speaker up in amplified mode with the common ground.
The amplified speaker you mentioned would need to have an adapter for differential to single ended as it does use a single ended input. In your case, just for use of the amplified speaker, you would only need that isolation transformer you linked to alone between the amplified speaker and the external speaker output of the 536. Be aware, however, that that speaker is expecting a low level input and could easily be overdriven with the output of the 536. The level adjust (R2 on the Motorola schematic for the HSN1006A) should be ok to use for this - I would start with the volume of the radio way down and adjust R2 on the HSN1006A only slightly above minimum and then very gradually turn the radio volume up. For maximum ease of use by you, I would probably set R2 on the HSN1006A to a point that allows the radio volume to be at the highest level you are likely to use it without distortion and then leave it there. Then you can just use the radio volume as needed. If I am understanding the manual properly, R2 is on the circuit board of the HSN1006A and is not easily adjustable from the outside of its enclosure; therefore, you would want to set it at a "comfortable" point and leave it thereafter only using the radio's volume control.
Given that the 536's BTL audio is pretty loud to begin with, I am assuming you are planning on using this in extremely noisy surroundings or else in a large area if you need that much extra amplification.
-Mike
I didn't mean to discredit your solution and knowledge on the topic. I guess my post came across the wrong way and I apologize. It was more directed towards those who don't have a good knowledge of electronics and if they can wait then before they experiment with something they don't fully understand and do something to cause damage to their units. Wait to see what Uniden's solution is when the App comes out because I really think it will be an IP based solution and could address a lot of peoples issues. I just wish we could get some confirmation from Uniden on this if it is or isn't and why that is such a secretive answer for them.
With the IP based streaming it would require no physical connection to the PC as it will all be internal from the scanner through an internal web server over WiFi which I am sure will be released in a firmware update when the App is launched. This would be the most reasonable solution to all of this. I just wish if this was their plan they they would have at least offered a RJ-45 jack for those who would like to and can hardwire their scanners to their routers because even as great as WiFi is I am sure in some peoples environments it could cause buffering and lag issues with the stream if they don't have a great WiFi connection. So I am interested to see what approach Uniden is going to take with all this. It is the only logical explanation as to why they removed the rec out jack to begin with because it will be a IP base stream internally.
MesquiteWX, hey no worries! Don't sweat it; I didn't really take it that way anyway. I understand the criticisms - the "more technical" solutions I gave were for those who are comfortable with "rolling their own" with a soldering iron and basic electronics parts. Otherwise, for those who can't or won't touch a soldering iron and any electronic components, I figured the info might still be useful and would at least shed some light on why things work the way they do. Just remember, a lot of people in this hobby do like to work on their own stuff and "get down and dirty" with the parts and the soldering iron so, for them a schematic to play with is part of the "fun". If you're not into that - no biggie, maybe the ancillary
information will still be of value in helping you find a more comfortable and appropriate "plug and play" solution!
Anyway, for any still interested and who like to tinker and build there own stuff, I am working on an improved version of my previous design as well as three other variations; two with just a fixed level attenuator (one with and one without a transformer) and a third which has a level control but uses a transformer rather than the direct connection used on my first design; all of these are passive circuits, no active components (but I'm thinking about those as well, now;-). When I've worked out some details I'll post the schematics here as before. I've done a lot of research since my last post and boned up a lot on BTL amps and audio engineering practices in general. For one thing, I'm primarily an RF guy and have my head crammed full of impedance matching techniques and practices so I had to refocus my perspective towards a "voltage matching and impedance bridging" way of thinking as is done in the audio world. I found a truly excellent article for anyone interested at Understanding Impedance. It's basic stuff but it clearly outlines the modern methodology of audio engineering relative to the telecom mindset (where I come from). It's a good read for anyone really who has any interest in the concept of impedance and level matching, etc. It's not heavy at all and is really intended for a general audience so don't be afraid to check it out - no heavy math or major assumptions on what you should already know - starts out super basic and works its way up. I think the author did a really fantastic job clearly outlining the concepts. Anyway, that article plus many others I've read have influenced my newer designs (if you can call them that - they are really simple compared to what I used to work with but, still, it's been fun and interesting for me to think outside the RF realm for a change).
-Mike
information will still be of value in helping you find a more comfortable and appropriate "plug and play" solution!
Anyway, for any still interested and who like to tinker and build there own stuff, I am working on an improved version of my previous design as well as three other variations; two with just a fixed level attenuator (one with and one without a transformer) and a third which has a level control but uses a transformer rather than the direct connection used on my first design; all of these are passive circuits, no active components (but I'm thinking about those as well, now;-). When I've worked out some details I'll post the schematics here as before. I've done a lot of research since my last post and boned up a lot on BTL amps and audio engineering practices in general. For one thing, I'm primarily an RF guy and have my head crammed full of impedance matching techniques and practices so I had to refocus my perspective towards a "voltage matching and impedance bridging" way of thinking as is done in the audio world. I found a truly excellent article for anyone interested at Understanding Impedance. It's basic stuff but it clearly outlines the modern methodology of audio engineering relative to the telecom mindset (where I come from). It's a good read for anyone really who has any interest in the concept of impedance and level matching, etc. It's not heavy at all and is really intended for a general audience so don't be afraid to check it out - no heavy math or major assumptions on what you should already know - starts out super basic and works its way up. I think the author did a really fantastic job clearly outlining the concepts. Anyway, that article plus many others I've read have influenced my newer designs (if you can call them that - they are really simple compared to what I used to work with but, still, it's been fun and interesting for me to think outside the RF realm for a change).
-Mike
Last edited:
JamesO
Member
Mike_G_D,.
Have you run into and hear the digital cross talk/switching noise on the external speaker output yet?
My radio has a noticeable digital cross talk/switching noise once the squelch unmutes. It is there during pauses in conversations and is a bit more obvious once the transmission stops and before the scanner resumes scanning.
It is kink of a function of the external speaker as how easy it is to hear. The speaker efficiency and speaker frequency response and make this noise more or less apparent.
If you want to sample this easily, assuming your hearing is not compromised in the higher frequency bands, plug a pair if earbuds into the external speaker connection point with the volume turned WAY down. The slowing increase the volume until you get to a comfortable listening level and you should easily hear the noise before the squelch mutes.
This noise may make it through to sound cards and recordings depending on the volume levels needed and other factors. Not sure it can easily be filtered out after the fact and if the Uniden "headphone" repair will address this issue??
Have you run into and hear the digital cross talk/switching noise on the external speaker output yet?
My radio has a noticeable digital cross talk/switching noise once the squelch unmutes. It is there during pauses in conversations and is a bit more obvious once the transmission stops and before the scanner resumes scanning.
It is kink of a function of the external speaker as how easy it is to hear. The speaker efficiency and speaker frequency response and make this noise more or less apparent.
If you want to sample this easily, assuming your hearing is not compromised in the higher frequency bands, plug a pair if earbuds into the external speaker connection point with the volume turned WAY down. The slowing increase the volume until you get to a comfortable listening level and you should easily hear the noise before the squelch mutes.
This noise may make it through to sound cards and recordings depending on the volume levels needed and other factors. Not sure it can easily be filtered out after the fact and if the Uniden "headphone" repair will address this issue??
JamesO
Member
Just checked, my scanner has band plan info in it, but I did not program the band plan into Sentinel.
The only think I did was program the 6 site frequencies into the radio, not even sure I needed to do this, but when in doubt, I did program all the site frequencies in.
System is set as a P25 trunked system.
I have 13 Talk Groups programmed in for VSP, however, I have stayed lock on Fairfax 2 for a long time just to see how stable the comms were. So I have not spent much time into actually scanning the system as I wanted to make sure things were stable.
If there is no band plan in the radio, I am guess something is not programmed correctly or you are unable to find the control channel.
I would manually try to lock onto the control channel and make sure you can reliably receive it.
The only think I did was program the 6 site frequencies into the radio, not even sure I needed to do this, but when in doubt, I did program all the site frequencies in.
System is set as a P25 trunked system.
I have 13 Talk Groups programmed in for VSP, however, I have stayed lock on Fairfax 2 for a long time just to see how stable the comms were. So I have not spent much time into actually scanning the system as I wanted to make sure things were stable.
If there is no band plan in the radio, I am guess something is not programmed correctly or you are unable to find the control channel.
I would manually try to lock onto the control channel and make sure you can reliably receive it.
Ok, for those interested in ideas and plans for "rolling their own" external speaker-to-PC audio adapters I created four passive adapter versions and am attaching these in .png formats rolled up in a zip file.
Two use fixed attenuators that reduce the external speaker output a fixed level (well over 10:1 depending on what PC input you use, mic or line, you can use either but it will reduce more with the mic input - which you'd want anyway). One of these uses a direct cap coupled design while the other uses a 1:1 transformer. Both now have a header/jumper selection so that you can use them either with the BTL output on the new Uniden 536 and other BTL speaker output radios or with regular single ended grounded negative speaker outputs (jumper position 1 is for BTL [pin 1 is a no connect and is jumped to pin 2] outputs and position 2 for standard speaker outputs [pin 2 is jumped to pin 3 - grounds the negative lead]) - having no jumper at all will make it work as BTL mode which is safe for BTL outputs. Because of the transformer in the second version, there is an extra header for bypassing the transformer - the transformer version could really be used with BTL and non-BTL outputs with no changes but for maximum flexibility I included the capability to ground the negative input lead as in the direct coupled version as well as bypassing the transformer entirely (which pretty much changes it to look basically like the direct coupled version). Again, no jumpers installed makes it work for BTL outputs safely.
They also now have a special ground return select switch for convenience in dealing with ground loop issues. Selection allows standard ground connected DC between PC and radio, ac coupling through capacitors, and no connection (isolated).
The two other versions use a variable attenuator for finer user selectable adjustment of the attenuation; the midway position should be approximately equivalent to what the fixed versions are set for. Again, one version uses a transformer while the other does not. Otherwise, these versions are essentially identical to the two fixed versions.
I also made all versions include a jack for connecting an external speaker to allow one to use a speaker while also using the interface if desired. Be aware that it is intended to be used in "long term fashion" - that is, not for frequent speaker unplugging/plugging or changes as the output level will lower significantly as designed when a speaker is plugged in. I could have made it so that it would not do this but that would have entailed the inclusion of a power 8 ohm "dummy load" resistor and switching jack which switches out the "dummy load" when the speaker is plugged in. This would have added to the cost and complexity, not to mention adding the need for a good power resistor (at least 10 watts to be safe) and possibly (likely) some form of heat dissipation/sink. So I went with a simpler design in the hopes that most people will likely be using it either with no speaker or with one main speaker that they don't change often anyway. Just be aware that as is, you will get a level change at the PC input when a speaker is plugged in or disconnected.
If you can afford them, tantalum caps would be best to use but standard aluminum electrolytics should work ok. If you can get or have access to some non-polarized electrolytics using one of those in place of the back-to-back two used for the ac coupled ground selection would be a better choice.
I sort of "over designed" in places because I don't have a 536 to test and do not know how its BTL outputs really look electrically. Therefore, I cap coupled both sides of the non-transformer adapter versions as I don't know if there is any DC present on the BTL outputs and how that may compare with the DC from a PC mic input's "phantom power"; again, non-polarized caps would be better here if you have them but I think that pointing the + lead of standard electrolytic caps toward there respective "sources" will be fine as long as you make the caps no less than around 10V capable. I've seen lots of ceramics now that reach up into the 100's of microfarads so if you have those or can get them then they may also be good choices instead of non-polarized electrolytics. Use what you've got and use good electronic "common sense".
In all cases, you could simplify the designs by eliminating the little "extras" like the BTL/Standard jumpers, ground selectors, and external speaker jacks if you don't need any or all of those. Also, the 1000pF shunt caps are there for bypassing RF high frequency "gunk" to ground - you could probably leave them out and not have any issues - some setups may need them more than others.
I didn't include manufacturer part numbers, wattage levels, tolerances, etc. I figured that most of those interested in this would know what to look for and where they most desire to get their parts. I don't see a need, as designed, to use anything more than 1/4 watt 5% tolerance resistors and standard 10 to 20% tolerance caps but if you have better stuff and/or can afford them then, by all means go for it! Again, better caps such as tantalum are good for the series audio lines if you can afford them and non-polarized if possible. The shunt resistor, R4, on the direct coupled non-transformer versions acts as a sort of "quasi dummy load" for the BTL output but - not really - it could be eliminated but it's there to give something to bring both leads of the BTL output line to rather than leaving one floating at the radio (which you could do, I just "felt better" bringing it up to the converter/adapter plus it allowed me to make it easy to use a jumper to convert the circuit for standard non-BTL speaker output use). It is not a "real" dummy load in that that would, again, necessitate the need for a 10 watt power resistor (I double expected needs for good safety practices - the 536 is rated for a 5 watt output to the external speaker jack) and the switching external speaker jack meaning more expense and heating issues. As is, the 500 ohm resistor should do ok at 1/4 watt but you if you have a beefier wattage version (anything around that resistance or so) than that would be the place to put it. Once the circuit is constructed, one of the first tests I would make is to output a strong level audio signal from the external speaker jack and use an oscilloscope to measure the voltage swing across that resistor. That will give you an idea what the best wattage version should be (as is, a 1/4 watt 500 ohm resistor should handle a 10 volt load ok for a short time; obviously, a higher wattage resistor would handle more; I know the 536 is rated at 5 watts into 8 ohms so that is about a 6 volt swing across 8 ohms not counting any DC present). If you're paranoid - just eliminate that resistor altogether; it'll work ok without it. Also, I didn't include any info on the transformer - just didn't get around to looking into this. Basically, just use a decent 1:1 audio isolation transformer with decent power handling capability (I'd stay with several watts just to be safe though, as designed, due to the high reflected impedances involved I don't think that you'd need much over a watt or so at most).
Basically, these are just "fun" designs for me to throw out there for do-it-yourself folks to play with if they have the means and knowledge. I included a lot of notes and pictures in the schematics to help illustrate things like how it should be connected and what kinds of interconnecting cables to use, etc.
-Mike
Two use fixed attenuators that reduce the external speaker output a fixed level (well over 10:1 depending on what PC input you use, mic or line, you can use either but it will reduce more with the mic input - which you'd want anyway). One of these uses a direct cap coupled design while the other uses a 1:1 transformer. Both now have a header/jumper selection so that you can use them either with the BTL output on the new Uniden 536 and other BTL speaker output radios or with regular single ended grounded negative speaker outputs (jumper position 1 is for BTL [pin 1 is a no connect and is jumped to pin 2] outputs and position 2 for standard speaker outputs [pin 2 is jumped to pin 3 - grounds the negative lead]) - having no jumper at all will make it work as BTL mode which is safe for BTL outputs. Because of the transformer in the second version, there is an extra header for bypassing the transformer - the transformer version could really be used with BTL and non-BTL outputs with no changes but for maximum flexibility I included the capability to ground the negative input lead as in the direct coupled version as well as bypassing the transformer entirely (which pretty much changes it to look basically like the direct coupled version). Again, no jumpers installed makes it work for BTL outputs safely.
They also now have a special ground return select switch for convenience in dealing with ground loop issues. Selection allows standard ground connected DC between PC and radio, ac coupling through capacitors, and no connection (isolated).
The two other versions use a variable attenuator for finer user selectable adjustment of the attenuation; the midway position should be approximately equivalent to what the fixed versions are set for. Again, one version uses a transformer while the other does not. Otherwise, these versions are essentially identical to the two fixed versions.
I also made all versions include a jack for connecting an external speaker to allow one to use a speaker while also using the interface if desired. Be aware that it is intended to be used in "long term fashion" - that is, not for frequent speaker unplugging/plugging or changes as the output level will lower significantly as designed when a speaker is plugged in. I could have made it so that it would not do this but that would have entailed the inclusion of a power 8 ohm "dummy load" resistor and switching jack which switches out the "dummy load" when the speaker is plugged in. This would have added to the cost and complexity, not to mention adding the need for a good power resistor (at least 10 watts to be safe) and possibly (likely) some form of heat dissipation/sink. So I went with a simpler design in the hopes that most people will likely be using it either with no speaker or with one main speaker that they don't change often anyway. Just be aware that as is, you will get a level change at the PC input when a speaker is plugged in or disconnected.
If you can afford them, tantalum caps would be best to use but standard aluminum electrolytics should work ok. If you can get or have access to some non-polarized electrolytics using one of those in place of the back-to-back two used for the ac coupled ground selection would be a better choice.
I sort of "over designed" in places because I don't have a 536 to test and do not know how its BTL outputs really look electrically. Therefore, I cap coupled both sides of the non-transformer adapter versions as I don't know if there is any DC present on the BTL outputs and how that may compare with the DC from a PC mic input's "phantom power"; again, non-polarized caps would be better here if you have them but I think that pointing the + lead of standard electrolytic caps toward there respective "sources" will be fine as long as you make the caps no less than around 10V capable. I've seen lots of ceramics now that reach up into the 100's of microfarads so if you have those or can get them then they may also be good choices instead of non-polarized electrolytics. Use what you've got and use good electronic "common sense".
In all cases, you could simplify the designs by eliminating the little "extras" like the BTL/Standard jumpers, ground selectors, and external speaker jacks if you don't need any or all of those. Also, the 1000pF shunt caps are there for bypassing RF high frequency "gunk" to ground - you could probably leave them out and not have any issues - some setups may need them more than others.
I didn't include manufacturer part numbers, wattage levels, tolerances, etc. I figured that most of those interested in this would know what to look for and where they most desire to get their parts. I don't see a need, as designed, to use anything more than 1/4 watt 5% tolerance resistors and standard 10 to 20% tolerance caps but if you have better stuff and/or can afford them then, by all means go for it! Again, better caps such as tantalum are good for the series audio lines if you can afford them and non-polarized if possible. The shunt resistor, R4, on the direct coupled non-transformer versions acts as a sort of "quasi dummy load" for the BTL output but - not really - it could be eliminated but it's there to give something to bring both leads of the BTL output line to rather than leaving one floating at the radio (which you could do, I just "felt better" bringing it up to the converter/adapter plus it allowed me to make it easy to use a jumper to convert the circuit for standard non-BTL speaker output use). It is not a "real" dummy load in that that would, again, necessitate the need for a 10 watt power resistor (I double expected needs for good safety practices - the 536 is rated for a 5 watt output to the external speaker jack) and the switching external speaker jack meaning more expense and heating issues. As is, the 500 ohm resistor should do ok at 1/4 watt but you if you have a beefier wattage version (anything around that resistance or so) than that would be the place to put it. Once the circuit is constructed, one of the first tests I would make is to output a strong level audio signal from the external speaker jack and use an oscilloscope to measure the voltage swing across that resistor. That will give you an idea what the best wattage version should be (as is, a 1/4 watt 500 ohm resistor should handle a 10 volt load ok for a short time; obviously, a higher wattage resistor would handle more; I know the 536 is rated at 5 watts into 8 ohms so that is about a 6 volt swing across 8 ohms not counting any DC present). If you're paranoid - just eliminate that resistor altogether; it'll work ok without it. Also, I didn't include any info on the transformer - just didn't get around to looking into this. Basically, just use a decent 1:1 audio isolation transformer with decent power handling capability (I'd stay with several watts just to be safe though, as designed, due to the high reflected impedances involved I don't think that you'd need much over a watt or so at most).
Basically, these are just "fun" designs for me to throw out there for do-it-yourself folks to play with if they have the means and knowledge. I included a lot of notes and pictures in the schematics to help illustrate things like how it should be connected and what kinds of interconnecting cables to use, etc.
-Mike
Last edited:
Unfortunately, I don't have a 536 to test - not in a position financially to obtain one in the foreseeable future. I have noticed things like what you describe on older stuff, however. The severity varies, of course. I would think that it could be filtered out if it primarily involves audio frequencies above the usual LMR expected voice range (above about 2.5KHz or so). But if the stuff you are hearing is in the voice range then it will be tough to get rid of after the fact. It SHOULD have been taken care of internally through decent power supply and audio circuit high frequency bypassing but, again, if the stuff is in the voice range it's not so easy - you need to get rid of it at the source (.e.g. using supply bypassing caps sufficient for audio range at the sources' power supply leads; at least for supply coupled sources). Depending on the design, this can be problematic.
Also, FWIW, I don't have a schematic of the 536, of course, so I can only speculate but I would be surprised if the headphone and speaker circuitry were that closely tied together. I would think that they would be completely separate circuits and that is what Upman has claimed. I see no reason to doubt him on this as that would make complete engineering sense to me.
-Mike
Ben96cal
Member
re; 536
I've noticed degrading volume on Uniden scanners since the 15x came out. Will the Ground Isolation Transformer - 3.5mm M/F work on all scanners? I'd like to put them on all my audio lines but want to make sure I won't blow anything up as I have some ground loop issues that have been bugging me for a long time.
I've noticed degrading volume on Uniden scanners since the 15x came out. Will the Ground Isolation Transformer - 3.5mm M/F work on all scanners? I'd like to put them on all my audio lines but want to make sure I won't blow anything up as I have some ground loop issues that have been bugging me for a long time.
- Status
