BCD536HP Discriminator and inside look

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n3617400

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hp1:
1st if: 380.075 mhz / 265.550 mhz
2st if: 20.85 mhz or 21.305 mhz (crystal is 21.305 mhz)
3st if: 455 khz
 

Mike_G_D

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hp1:
1st if: 380.075 mhz / 265.550 mhz
2st if: 20.85 mhz or 21.305 mhz (crystal is 21.305 mhz)
3st if: 455 khz

Your 2nd IF in that list contains two entries, 20.85MHz and 21.305MHz, the difference between the two is 455KHz so one of those is the 2nd Local Oscilator (LO). Since you say, "crystal is 21.305mhz", that makes me pretty sure that that is the 2nd LO frequency while the lower of the two is the actual 2nd IF that it mixes with to produce the 3rd and final IF.

Interesting that there is such a difference between the HP1 and XT RF designs. Makes me wonder all the more so about the x36 series. If someone could locate the 2nd LO stage on an x36 radio and read off what that frequency is (if possible) it would help us determine the resulting IF (if we know the exact 3rd IF frequency or 3rd LO).

-Mike
 

Boatanchor

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hp1:
1st if: 380.075 mhz / 265.550 mhz
2st if: 20.85 mhz or 21.305 mhz (crystal is 21.305 mhz)
3st if: 455 khz

Those HP1 IF frequencies that you listed are at least partially incorrect.
For a start, some people here have been replacing the 3rd IF filter in the HP1 with the Murata 450Khz filter that we have been fitting to the XT series, so the 3rd IF is definitely not 455Khz.

I don't know where you obtained the 2nd IF's from.
I don't own a HP1 so I can't confirm, but I'd be stunned if the HP1 2nd IF was not 10.8Mhz like the XT series.

As for the x36HP's, the RF stages look so similar (from a distance) to the xt series, that I doubt that even it uses a significantly different RF/IF configuration. --- If it ain't broke..
 

Mike_G_D

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I tend to agree with Boatanchor on this, n3617400, I'd double check your info, especially since you admitted the 455KHz error - could the 2nd IF info you have be incorrect? Where/how did you obtain that info?

-Mike
 

n3617400

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I was wrong twice. oscillator - 21.3 MHz and 3st if: 450 khz

hp1:
1st if: 380.075 mhz / 265.550 mhz
2st if: 20.85 mhz
3st if: 450 khz
 

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Mike_G_D

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Well, it sure looks like the HP1 uses a 2nd IF of 20.85MHz with a 3rd LO of 21.300MHz to mix it down to a 450KHz 3rd and final IF.

Why the difference from the XT series in terms of the 2nd IF I don't know. Interesting, though.

I'm thinking that the last picture shows the 20.85MHz IF filter.

So the new x36 series - could go either way or something else entirely.

Unfortunately for me, my only "lab" available is my mind. No access to real test equipment or appropriate DUT's! My only input is what I can glean from the web including this site/forum.

If I had it all (appropriate test equipment and devices to test) actually in front of me I could figure it all out quite quickly; I also seriously miss the days when schematics and block diagrams were included with the user manuals and service manuals were not that hard to obtain (I loved the SAM's [think that's what they were called] service guides!)!

-Mike
 

FeedForward

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What I noticed from your photos is that there are 2 ceramic filters side by side. One is a 50G and the other is a 50E type. For those familiar with the 996XT thread, apparently the designers decided to go with the G filter as suggested in the other thread. But not only that, it looks as if 2 filters are operational and selected according to the modulation type of the received signal. I'd say that technique is the best of both worlds and certainly confirms the validity of switching to the G filter in the 996XT. Of course, it would be great to have a good block diagram if nothing else than to get a grip on how the scanner is designed.

FeedForward
 

scanboyca

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As was already mentioned the orange is only for backlight.

I'm interested in simulating turning it off with by knob by using a relay. I'd have the power wire go to battery (always hot) , and the new ignition sense to accessory power (switched).

This would allow the radio to write settings to the memory, and power down.

Has anyone posted information on how to modify the BCD536HP to allow accessory power to control scanner on/off (similar to using the power on/off knob). I would like to do this to my scanner.... Not for automotive use but rather mo remotely power cycle my scanner when the wifi network connection dies. This happens a couple of times a day when streaming audio over wifi. I can still ping the scanner but can't reconnect to restart streaming without cycling scanner power.
 

Voyager

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No - it's part of the volume control. The control consists of a switch for the power to the micro. It's that line you want to interrupt for a soft power-down (the type that writes the card and shuts off). Someone recently posted about a jumper that exists for that line that you would remove and interrupt the line there. I don't have the exact post however.

I REALLY wish Uniden would add the flag in the firmware to let the dim line serve as an ignition control. I suggested that when they first came out. It would be SUCH an easy firmware addition, and would solve this issue.
 

scanboyca

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No - it's part of the volume control. The control consists of a switch for the power to the micro. It's that line you want to interrupt for a soft power-down (the type that writes the card and shuts off). Someone recently posted about a jumper that exists for that line that you would remove and interrupt the line there. I don't have the exact post however.

I REALLY wish Uniden would add the flag in the firmware to let the dim line serve as an ignition control. I suggested that when they first came out. It would be SUCH an easy firmware addition, and would solve this issue.

Yes. Thank you. This is what I'm interested in doing. A "soft power down" so settings are saved and SD card is less likely to get corrupted. Have you seen any postings where others have done this already? I don't want to reinvent the wheel here.
 

Voyager

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I've seen a post where someone (about a week ago or so) was talking about a jumper they removed (I think) and used that point to control the power - exactly what you want to do. Maybe they will post it here or someone will recall which thread it was in.

Maybe search the forums for the key words: BCD536HP power jumper
 

N0BDW

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Sorry to bump an old thread.

I'm using a 536 to feed into a mixer then out to overhead speakers in our fire hall. I've found that in order to get reasonable audio quality the volume control on the 536 has to be maxed (29) and the volume on the channel on the mixer has to be set extremely low or we get a hum on the speakers.

But the audio we do get sounds a bit muffled and bassy. The treble on the mixer is all the way up and the bass is all the way down. Would tapping the discriminator help with that?

The PA from the phone system is hooked up to the next channel over and sounds fine.
 

redbeard

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Sorry to bump an old thread.

I'm using a 536 to feed into a mixer then out to overhead speakers in our fire hall. I've found that in order to get reasonable audio quality the volume control on the 536 has to be maxed (29) and the volume on the channel on the mixer has to be set extremely low or we get a hum on the speakers.

But the audio we do get sounds a bit muffled and bassy. The treble on the mixer is all the way up and the bass is all the way down. Would tapping the discriminator help with that?

The PA from the phone system is hooked up to the next channel over and sounds fine.

You have a couple problems, impedence mismatch and the type of audio amplifier in the 536. You might consider switching to a 996P2 if you need phase 2 or just a regular 996 for p25 or a 15X if you don't need digital. I mention those scanners because they have a dedicated recording output that is at the proper impedence.

A discriminator tap would give you raw, unfiltered signal with no digital decoding suitable only for connecting to a computer to decode. So no, it would not help at all.

See this thread for more info:
http://forums.radioreference.com/un...er-connection-considerations-precautions.html
 

N0BDW

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You have a couple problems, impedence mismatch and the type of audio amplifier in the 536. You might consider switching to a 996P2 if you need phase 2 or just a regular 996 for p25 or a 15X if you don't need digital. I mention those scanners because they have a dedicated recording output that is at the proper impedence.

A discriminator tap would give you raw, unfiltered signal with no digital decoding suitable only for connecting to a computer to decode. So no, it would not help at all.

See this thread for more info:
http://forums.radioreference.com/un...er-connection-considerations-precautions.html

Thank you.
 

N9JIG

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I concur with redbeard's suggestion for a 996 to replace the 536 for your installation. The lack of a record jack is probably the biggest issue I have with the 536.

Little side story here:
When our FD alert system failed a few years ago I did a temp job with a BCT15X set for two-tone alert into the PA system and we ran that for a few weeks until the new receiver arrived. Worked like a champ! When the new receiver came in from Veetronics I realized it was basically a BC355 modified with a tone board and relay but minus the keyboard. The "Programming Kit" arrived separately a couple days later, it was the keyboard they removed from the scanner...
 

ProScan

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Sorry to bump an old thread.

I'm using a 536 to feed into a mixer then out to overhead speakers in our fire hall. I've found that in order to get reasonable audio quality the volume control on the 536 has to be maxed (29) and the volume on the channel on the mixer has to be set extremely low or we get a hum on the speakers.

But the audio we do get sounds a bit muffled and bassy. The treble on the mixer is all the way up and the bass is all the way down. Would tapping the discriminator help with that?

The PA from the phone system is hooked up to the next channel over and sounds fine.

I would first try to eliminate the hum by trying a ground loop isolator (1:1 audio transformer) and once the hum is removed then turn the scanner volume to somewhere around 40% or less than turn up the mixer input.

{edit} I think the muffled and bassy effect is caused by the scanner volume turned up to high causing saturation or clipping of the scanner audio amp final stage.
 
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