eorange
♦RF Enabled Member♦
Having worked with realtime bitstream processing (but not in the radio world), I'd guess it's the processing algorithms with better fault tolerance, error handling, and recovery.
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How can we design a diversity antenna system to see if it can improve reception in an LSM environment? Would 2 yagi antennas connected to a combiner be sufficient and experiment with placement?
mully95
Member
From what I understand is that it's not the antenna side.... it's the scanner. You can have a ton of antennas and it's not going to change anything with decoding. The problem lies with the decoding not the signal....however this is my personal thoughts.... I could be wrong.
What doesn't help is the fact that Motorola uses some of the manufacturer-specific proprietary data part of the P25 format to enhance the voice data. I don't think anyone else can use that without copyright violation issues.
Joe M.
The decoding is straightforward if the symbols (data) can be distinguished in the received signal. Improving signal improves performance because there is more data recovered for decoding.
So again my question: Will a diversity antenna system improve the signal thereby improving the data recovery? And how can it be designed? This can be an inexpensive solution until Uniden can fix the issue in their scanners.
Yes, a diversity antenna system would dramatically improve performance in any multipath situation. However, it is not an inexpensive solution (involves much more than just using 2 antennas). Wikipedia has a fairly decent explanation. Here is a snippet:
I was tempted to change most of the "s"'s to "$" in the above quote.
Hi UpMan,
It looks like a spatial diversity antenna system would help reduce the multi path. It's worth a shot to experiment. I am going to create another thread on this subject and hopefully with some help figure out a temporary solution.
thanks!
Joe
It looks like a spatial diversity antenna system would help reduce the multi path. It's worth a shot to experiment. I am going to create another thread on this subject and hopefully with some help figure out a temporary solution.
thanks!
Joe
The problem with having two antennas both coupled to the antenna jack is that now you'll have signal interference (both destructive and constructive) in the antenna feed line. If you look at processing technique, only combining keeps both antennas active at the same time, and in both cases, there is some active circuitry used to determine how the signals from all antennas are combined.
Hi UPMan,
I started another thread on this topic in the general scanner forum (before I read your last post). Maybe we can discuss the plusses and minuses of such a system there.
thanks for your help!
I started another thread on this topic in the general scanner forum (before I read your last post). Maybe we can discuss the plusses and minuses of such a system there.
thanks for your help!
How about we keep the conversation to one thread?
When you start splitting it off into multiple threads in multiple forums confusion starts to reign.
Marshall KE4ZNR
Understood, however I already started the other thread. Reason being that this thread's topic is about loose squelch improving LSM reception.
The cost must not be that prohibitive as many of the cheap wireless network access points have a diversity antenna system. ???????
And what range of frequencies and how many different demodulation modes do they use?
I must admit to some surprise at hearing that serious consideration is being given to employing diversity antenna systems on portable scanner equipment as a possible solution to the simulcast reception issue.
Have we conclusively determined that the methodology employed by professional subscriber equipment to deal with simulcast interference is too impractical to implement in a $600 or less consumer scanner? I know of no current professional LMR portable gear that uses diversity antenna technology. I may be wrong but I am skeptical of that being the primary solution (diversity antenna systems).
There are many reasons that using a diversity antenna solution would be impractical in a portable and possibly even mobile environment. As UpMan stated, we are dealing with many wavelengths here - even if we limit the solutions to 150MHz and above that still means we are dealing with wavelengths that range from about 6.5 feet at 150MHz to about a foot at 960MHz. For a quarter wave element we are saying between 19.5 inches at 150MHz to about 3 inches at 960MHz, give or take. For a diversity antenna to work well and effectively it should contain two or more equally effective antennas for a given desired frequency range. At the 2.4GHz range of 802.11bgn wireless systems this is practical given that the antennas are small - less than 5 inches for a full wavelength and a tad over 1 inch for a quarter wavelength and electrically shortening them, if necessary, is far simpler and less inefficient than at much lower, sub-1GHz frequencies. To electrically shorten a 150MHz antenna to fit within a small handheld device would make it very inefficient and so poor a performer relative to even a basic stock "rubber ducky" that if it were employed as a "second" antenna in a diversity antenna system it would be nearly useless. Yes, at 700MHz and up you MIGHT be able to accommodate this solution to some reasonable degree of effectiveness in a handheld device but it would still not be ideal unless you literally had two or more actual identical tuned antennas sporting physically from the device - pretty ungainly for the average user to hold in a comfortable manner. At the higher frequencies, 700MHz and up, a less efficient built-in antenna might work as a second antenna in tandem with the primary attached whip or ducky but the discrepancy between the two would mean that the user would only benefit at higher signal levels - the diversity system would only really be effective based on the signal levels coming from the least efficient antenna.
For fixed use it is a reasonable solution though pricey if for no other reason than the cost of the extra antennas, feedlines, and switching gear. For mobile use - maybe with the same issues plus less physical space, etc. For a handheld, it's tough, at least for lower frequencies.
And the above isn't even considering the many other aspects of correctly and effectively using a diversity antenna system such as implementing the logic to differentiate between signal qualities at each antenna - signal level is relatively easy but better effectiveness, especially for digital LMR systems, might be to compare BER (bit error rate) and ISI (inter-symbol interference) between the two. And this would have to be done for multiple methods of digital modulation if you are dealing with multiple digital modes. All of the extra RF plumbing also adds loss and noise to the system and provides even more potential paths for interference such as spurious signal generation, intermodulation, etc., which are already serious issues in consumer scanner radios.
I think that actually giving serious consideration to using diversity antenna solutions as a means to deal with LMR simulcast distortion (for those systems that use simulcast methods) should only be a last resort when faced with, possibly, the following cases:
1) Any reception outside of the intended service area that the simulcast system is optimized for; and
2) If it is absolutely confirmed that using the same methodology, whatever it may be, as is used in the professional subscriber gear is simply too costly or otherwise impractical to implement in consumer $600 or less scanner gear (yes, this assumes that said gear is not using a diversity antenna system to deal with simulcast distortion - an assumption I think is a practical and likely valid one).
-Mike
Have we conclusively determined that the methodology employed by professional subscriber equipment to deal with simulcast interference is too impractical to implement in a $600 or less consumer scanner? I know of no current professional LMR portable gear that uses diversity antenna technology. I may be wrong but I am skeptical of that being the primary solution (diversity antenna systems).
There are many reasons that using a diversity antenna solution would be impractical in a portable and possibly even mobile environment. As UpMan stated, we are dealing with many wavelengths here - even if we limit the solutions to 150MHz and above that still means we are dealing with wavelengths that range from about 6.5 feet at 150MHz to about a foot at 960MHz. For a quarter wave element we are saying between 19.5 inches at 150MHz to about 3 inches at 960MHz, give or take. For a diversity antenna to work well and effectively it should contain two or more equally effective antennas for a given desired frequency range. At the 2.4GHz range of 802.11bgn wireless systems this is practical given that the antennas are small - less than 5 inches for a full wavelength and a tad over 1 inch for a quarter wavelength and electrically shortening them, if necessary, is far simpler and less inefficient than at much lower, sub-1GHz frequencies. To electrically shorten a 150MHz antenna to fit within a small handheld device would make it very inefficient and so poor a performer relative to even a basic stock "rubber ducky" that if it were employed as a "second" antenna in a diversity antenna system it would be nearly useless. Yes, at 700MHz and up you MIGHT be able to accommodate this solution to some reasonable degree of effectiveness in a handheld device but it would still not be ideal unless you literally had two or more actual identical tuned antennas sporting physically from the device - pretty ungainly for the average user to hold in a comfortable manner. At the higher frequencies, 700MHz and up, a less efficient built-in antenna might work as a second antenna in tandem with the primary attached whip or ducky but the discrepancy between the two would mean that the user would only benefit at higher signal levels - the diversity system would only really be effective based on the signal levels coming from the least efficient antenna.
For fixed use it is a reasonable solution though pricey if for no other reason than the cost of the extra antennas, feedlines, and switching gear. For mobile use - maybe with the same issues plus less physical space, etc. For a handheld, it's tough, at least for lower frequencies.
And the above isn't even considering the many other aspects of correctly and effectively using a diversity antenna system such as implementing the logic to differentiate between signal qualities at each antenna - signal level is relatively easy but better effectiveness, especially for digital LMR systems, might be to compare BER (bit error rate) and ISI (inter-symbol interference) between the two. And this would have to be done for multiple methods of digital modulation if you are dealing with multiple digital modes. All of the extra RF plumbing also adds loss and noise to the system and provides even more potential paths for interference such as spurious signal generation, intermodulation, etc., which are already serious issues in consumer scanner radios.
I think that actually giving serious consideration to using diversity antenna solutions as a means to deal with LMR simulcast distortion (for those systems that use simulcast methods) should only be a last resort when faced with, possibly, the following cases:
1) Any reception outside of the intended service area that the simulcast system is optimized for; and
2) If it is absolutely confirmed that using the same methodology, whatever it may be, as is used in the professional subscriber gear is simply too costly or otherwise impractical to implement in consumer $600 or less scanner gear (yes, this assumes that said gear is not using a diversity antenna system to deal with simulcast distortion - an assumption I think is a practical and likely valid one).
-Mike
So much for open standards.
I know the Motos use IQ data sent to the DSP over lines that use varying current instead of voltage which is sort of a unique idea. It apparently helps with RFI issues. I would assume the DSP is getting cleaner data to work with since it's receiving processed IQ data. Hopefully some day a major improvement can be made in the scanner world. As it is now simulcast may as well be encryption in my area.
I don't know if it would work, but perhaps a more sensitive and selective receiver would be a solution.
I also have to think that a huge part of the issue is how the system is set up since some systems work fine and others of the same type don't.
Joe M.
I also have to think that a huge part of the issue is how the system is set up since some systems work fine and others of the same type don't.
Joe M.
Rereading the thread this morning...DDan, didn't mean to sound like such a snark, but I see that my terse reply (I was posting from my phone, and am typically much less verbose) looked pretty snarky. Also incomplete...the ratio of sales of wireless routers to scanners is probably on the order of 100,000:1. Another factor that brings down cost.
Depends upon the frequency ...
As I noted previously, E.F. Johnson implemented diversity reception in their first mobile cellular radio (800 MHz band). I paid $299 for the radio new, and found the diversity reception feature highly beneficial in my car.
Somehow the "quote" feature dumped on me so I do my best here in the "old fashioned" manner:
AE7Q stated:
"As I noted previously, E.F. Johnson implemented diversity reception in their first mobile cellular radio (800 MHz band). I paid $299 for the radio new, and found the diversity reception feature highly beneficial in my car." (The word "highly" being emboldened for emphasis)
My reply:
That is a 800MHz (presumably) mobile cellular radio, however, not a typical LMR radio and certainly not a handheld unit. No matter how you slice it, implementing a true diversity antenna system in a handheld package would be a difficult task across a 150MHz to 1GHz range. Again, I am not saying that there are absolutely and definitively no LMR radios using spatial antenna diversity technology but that I am not aware of any in COMMON use and in typical use as a means to deal with simulcast system reception. If spatial antenna diversity is being used as a PRIMARY means to handle simulcast system reception I would be interested in seeing the designs! Also, even if that is the case, I would be surprised if it could work well below 700MHz in a handheld device.
As I stated in my earlier post, spatial antenna diversity technology could be a practical solution in fixed station use and some mobile environments but not so practical in handheld portable devices especially in sub-700MHz implementations.
Again, I am pretty sure that most, if not all, professional subscriber handheld gear used in digital LMR simulcast systems does not use true spatial antenna diversity as a means to handle reception. I maintain there are "other" means that are employed and the question is how difficult and/or expensive are those means in terms of implementing them in a consumer scanner for $600 or less? In a handheld 25MHz to 1GHz consumer scanner is spatial antenna diversity really a cheaper and more practical alternative?
Now, I want to apologize to everyone for going off-topic here - another thread was created by jcardani in the General sub-forum to discuss spatial antenna diversity and we should bring this discussion there and let this thread stay on the original topic. My earlier post was in reply to the discourse between UpMan and DDan primarily and I didn't think to take it to the other thread at the time.
-Mike
AE7Q stated:
"As I noted previously, E.F. Johnson implemented diversity reception in their first mobile cellular radio (800 MHz band). I paid $299 for the radio new, and found the diversity reception feature highly beneficial in my car." (The word "highly" being emboldened for emphasis)
My reply:
That is a 800MHz (presumably) mobile cellular radio, however, not a typical LMR radio and certainly not a handheld unit. No matter how you slice it, implementing a true diversity antenna system in a handheld package would be a difficult task across a 150MHz to 1GHz range. Again, I am not saying that there are absolutely and definitively no LMR radios using spatial antenna diversity technology but that I am not aware of any in COMMON use and in typical use as a means to deal with simulcast system reception. If spatial antenna diversity is being used as a PRIMARY means to handle simulcast system reception I would be interested in seeing the designs! Also, even if that is the case, I would be surprised if it could work well below 700MHz in a handheld device.
As I stated in my earlier post, spatial antenna diversity technology could be a practical solution in fixed station use and some mobile environments but not so practical in handheld portable devices especially in sub-700MHz implementations.
Again, I am pretty sure that most, if not all, professional subscriber handheld gear used in digital LMR simulcast systems does not use true spatial antenna diversity as a means to handle reception. I maintain there are "other" means that are employed and the question is how difficult and/or expensive are those means in terms of implementing them in a consumer scanner for $600 or less? In a handheld 25MHz to 1GHz consumer scanner is spatial antenna diversity really a cheaper and more practical alternative?
Now, I want to apologize to everyone for going off-topic here - another thread was created by jcardani in the General sub-forum to discuss spatial antenna diversity and we should bring this discussion there and let this thread stay on the original topic. My earlier post was in reply to the discourse between UpMan and DDan primarily and I didn't think to take it to the other thread at the time.
-Mike
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