Auto, NFM, or FM for your P25 chnnels?

[SOFA_KING]

What do you use for your fed P25 channels? Auto, NFM, or FM?

I usually used "Auto", but now I am experimenting with NFM. If I'm not mistaken these should be narrow FM, no? The reason I am trying this is to see if digital decoding is better in NFM mode. Many of my P25 channels were not decoding unless I had S-2 signal or beter. It is early yet to tell if it is working better programmed as NFM. So far the only difference I see is the squelch action. I have to turn the squelch up a bit or I get "sputter". I'm not crazy about that, but if I get better P25 decoding then it will be worth it.

I'm also changing the backup analog channels (with PL) for my P25 channels to NFM. This should all be narrow band now, no?

So what are your thoughts on this?

Phil

 

[SCPD]

I use Auto also, so I'd be curious where this one goes.

 

[MOTOROLANUT]

choice

Auto for me....Pro-106 & 197

 

[SOFA_KING]

I set up an experimental file with a distant P25 freq. I put one channel as P25 NFM and one as P25 FM on the same freq. The band is closed for the moment so I have to wait. Since each channel has a 50/50 chance of landing on activity for this freq, one should get more hits if there is any improvement one way or the other. Time will tell. I'll post the results.

Phil

 

[SOFA_KING]

I just caught a wave from the south and got twenty P25 decodes on my test freq (USSS Tango with that constant 2 minute belch). These are early results for P25 lock:

11 - NFM
09 - FM

Here are the early results for weak signal NAC decoding:

4 - NFM
2 - FM

The erly results are leaning towards NFM being better. More data will be presented as it comes in.

Phil

 

[SOFA_KING]

Final Test Results

The band was down and up with waves of stronger signal at times. Overall it was weak but did peak to S-4 at one point. I shut down the test after I stopped getting P25 locks. The results are interesting and should answer the question of what works better for P25 decoding...regular FM (includes "Auto") or NFM. Again, this was done with weak signal over 100 miles away (USSS Tango with it's 2 minute burps...Great for a test like this!). The scanner was programmed for two channels on the same frequency...One FM and the other NFM. Each had a 50/50 chance while scanning. The mode was P25 NAC Search. Here are the results:

WEAKER
18:11:52, 0006, CONV , USS T P25 NFM , 164.650000
18:15:59, 0006, CONV , USS T P25 NFM , 164.650000

STRONGER
18:18:20, 0006, CONV , USS T P25 NFM , 164.650000
18:20:38, 0006, CONV , USS T P25 NFM , 164.650000
18:20:42, 0007, CONV , USS T P25 FM , 164.650000, P25, 001
18:20:46, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
18:22:20, 0007, CONV , USS T P25 FM , 164.650000

GAP

STRONGER
18:41:28, 0007, CONV , USS T P25 FM , 164.650000
18:41:33, 0007, CONV , USS T P25 FM , 164.650000, P25, 001
18:41:44, 0006, CONV , USS T P25 NFM , 164.650000
18:41:48, 0006, CONV , USS T P25 NFM , 164.650000
18:41:52, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
18:42:00, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
18:43:46, 0007, CONV , USS T P25 FM , 164.650000
18:43:48, 0007, CONV , USS T P25 FM , 164.650000
18:43:52, 0006, CONV , USS T P25 NFM , 164.650000
18:43:57, 0007, CONV , USS T P25 FM , 164.650000

WEAKER
18:47:22, 0007, CONV , USS T P25 FM , 164.650000
18:47:34, 0007, CONV , USS T P25 FM , 164.650000
19:04:25, 0007, CONV , USS T P25 FM , 164.650000
19:04:30, 0007, CONV , USS T P25 FM , 164.650000
19:12:20, 0007, CONV , USS T P25 FM , 164.650000

STRONGER
19:24:21, 0006, CONV , USS T P25 NFM , 164.650000
19:26:25, 0007, CONV , USS T P25 FM , 164.650000
19:28:27, 0007, CONV , USS T P25 FM , 164.650000

WEAKER
19:36:20, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
19:40:24, 0007, CONV , USS T P25 FM , 164.650000

STRONGER
19:50:21, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
19:52:20, 0007, CONV , USS T P25 FM , 164.650000
19:54:29, 0007, CONV , USS T P25 FM , 164.650000
19:56:20, 0007, CONV , USS T P25 FM , 164.650000
19:56:48, 0006, CONV , USS T P25 NFM , 164.650000
19:58:20, 0007, CONV , USS T P25 FM , 164.650000, P25, 001
20:01:32, 0006, CONV , USS T P25 NFM , 164.650000
20:01:36, 0006, CONV , USS T P25 NFM , 164.650000
20:01:40, 0006, CONV , USS T P25 NFM , 164.650000
20:02:20, 0007, CONV , USS T P25 FM , 164.650000
20:04:20, 0007, CONV , USS T P25 FM , 164.650000, P25, 001
20:06:20, 0006, CONV , USS T P25 NFM , 164.650000
20:08:20, 0007, CONV , USS T P25 FM , 164.650000
20:10:07, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:10:28, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:12:20, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:15:23, 0007, CONV , USS T P25 FM , 164.650000

STRONGEST
20:20:24, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:22:20, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:24:21, 0007, CONV , USS T P25 FM , 164.650000
20:26:26, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:28:31, 0007, CONV , USS T P25 FM , 164.650000
20:30:28, 0006, CONV , USS T P25 NFM , 164.650000
20:32:31, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:34:27, 0007, CONV , USS T P25 FM , 164.650000, P25, 001
20:36:20, 0007, CONV , USS T P25 FM , 164.650000, P25, 001
20:38:20, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:40:35, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001

WEAKER
20:44:29, 0007, CONV , USS T P25 FM , 164.650000
20:48:20, 0006, CONV , USS T P25 NFM , 164.650000
20:50:20, 0006, CONV , USS T P25 NFM , 164.650000, P25, 001
20:54:20, 0006, CONV , USS T P25 NFM , 164.650000
21:08:25, 0006, CONV , USS T P25 NFM , 164.650000
21:20:20, 0006, CONV , USS T P25 NFM , 164.650000
21:22:20, 0006, CONV , USS T P25 NFM , 164.650000
21:26:24, 0007, CONV , USS T P25 FM , 164.650000
21:50:25, 0007, CONV , USS T P25 FM , 164.650000

END
------------------------------------------------------------------
64 total P25 locks
21 total NAC decodes

34 NFM P25 locks with 15 NAC decodes (53%/44%)
30 FM P25 locks with 6 NAC decodes (47%/20%)

9 WEAKER NFM P25 locks with 2 NAC decodes (22%)
9 WEAKER FM P25 locks with 0 NAC decodes (0%)

25 STRONGER NFM P25 locks with13 NAC decodes (52%)
21 STRONGER FM P25 decodes with 6 NAC decodes (29%)

Without any doubt, NFM works better on federal P25 frequencies (and narrow band analog if they use that) than regular FM and Auto (which is regular FM as the squelch setting reflects).

Phil

 

[w8jjr]

All feds are switching to NBFM

This may be why

 

[WayneH]

As it looks like you're using Win500 to log I'd say you've throw some error in just with that. Since it tends to operate strangely with NACs I wouldn't second guess it making things appear different than they are.

Whether FM is right or not there's going to be only one mode for P25 and my guess is the radio (GRE models in particular) are going to override the setting. P25 really isn't "FM" in any way. Considering your signal too I would still be a bit skeptical.

 

[SOFA_KING]

As it looks like you're using Win500 to log I'd say you've throw some error in just with that. Since it tends to operate strangely with NACs I wouldn't second guess it making things appear different than they are.

Whether FM is right or not there's going to be only one mode for P25 and my guess is the radio (GRE models in particular) are going to override the setting. P25 really isn't "FM" in any way. Considering your signal too I would still be a bit skeptical.

What error is in Win500? I don't "second guess it". If you are referring to the NAC carry-over issue, that is not Win500 doing that. It is the scanner. The NAC carry-over issue doesn't even matter since the test frequency only uses one NAC (001).

The data presented is unaltered. It had just as much of a chance to fall either way. With a sample size of 64 locks there is enough data to show a clear trend. I only put some notes in to indicate "stronger" or "weaker" signal based on missed P25 locks since we know this transmitter sends a data burst every two minutes. The ability for the scanner to decode the NAC during the stronger conditions would confirm this as well.

P25 may be a different "structured" way of modulating the carrier, but it does "deviate" the carrier just like analog FM or phase modulation, so how you set up the passband of the deviated carrier does matter. If you are changing that passband to match the deviated bandwidth, you are optimizing the discriminator's ability to decode the frequency shifts of the modulated carrier. Also, the general rule is that the more narrow the passband, the more sensitive the receiver becomes due to lower noise. This is basic theory. But the ability to get better data decoding has to do with the optimal discriminator passband.

Whatever anyone thinks, the test data is showing a clear trend. The test could have fallen either way, and there is nothing in the test procedure to influence the outcome one way or the other. If I get better results programming my P25 channels with NFM then I'm going to do that. If the signal is in fact "narrow band", then NFM is what should be used. The data from the test shows about a 22% better chance of decoding the P25 data using NFM (on weak to marginal signal). The test method was ideal in signal strength, and consistency of the test signal being transmitted at least every two minutes provided a good method of consistent repeatability.

One more note (maybe Don S could verify this): As far as I can tell, the scanner scans as FM or NFM when you program a channel that way. "Auto" does nothing more then set a default mode (FM/NFM/AM) based on what GRE thinks is the standard for that frequency band. It clearly has nothing to do with digital detection since setting a channel to FM or NFM still decodes P25, and notice DG is not a "Modulation" selection...only FM/NFM/AM/Auto. When the FM/NFM discriminator detects a signal above the squelch threshold (by noise measurements which change depending on the bandwidth) it stops the scan. Then it determines if P25 is present or not. If not, and you have that channel programmed as NAC, a logical signal is sent to the CPU to continue scanning. If P25 is detected, the logic switches the audio routing to the P25 decoded audio output (comes from the decoder instead of the discriminator) and you get the decoded digital audio instead of the analog discriminator audio. So if (and I do say if) this is the case, how you have the passband set on the discriminator will determine how optimal the data deviated carrier is detected and decoded. One more thing...the squelch action is different between NFM and FM. This is a sure sign that GRE has two different passbands depending on the mode and not just an "audio boost" on NFM like my Uniden scanners had. I think GRE did it right and the results speak for themselves.

Phil

 

[WayneH]

I asked someone who would know. They said the scanner defaults to FM mode. NFM is only applicable to analog transmissions.

If you think it helps, continue to use it. Sometimes the placebo effect works well for people. :lol:

 

[mtindor]

I asked someone who would know. They said the scanner defaults to FM mode. NFM is only applicable to analog transmissions.

If this is true [and it could be], it isn't sensible. If the idea behind having selection of NFM and FM is to narrow the passband and ultimately cut out some noise, then it would be as effective for analog or digital narrowband transmissions. We already know it is effective for analog when we know the analog sig is narrowband.

If you're saying that "somebody who knows" guarantees that the scanner always uses FM rather than NFM mode for digital transmissions, that's a flaw that shouldn't be - IMO.

SOFA's findings would back up what I would expect - better performance on digital when set to NFM if you know for a fact that the transmitted signal is narrowband.

Placebo or not, I also program all suspected 11 / 8 Khz freqs as NFM. I'd like to think that the scanner is doing what it should be doing.

Mike

 

[WayneH]

If you're saying that "somebody who knows" guarantees that the scanner always uses FM rather than NFM mode for digital transmissions, that's a flaw that shouldn't be - IMO.

I stand by the info given to me; it's not from someone making a guess.

Even though the scanner defaults to FM mode it doesn't necessarily mean it's not treating the signal appropriately. Considering GRE models have the best digital decode and correction I don't think there's something that simple to change like narrowing the passband.

In this case I think it's more a matter of perception.

 

[Mike_G_D]

This is an extremely interesting discussion about a topic of considerable interest to me. My own observations of how the GRE units handle FM versus NFM indicate that there is a significant IF bandwidth change between the two in analog mode as, it seems, all of you are in agreement with. However, I cannot as yet determine if the same can be said regarding P25 signals due to a lack of available and applicable test equipment on my part. It is much easier to determine adjacent channel interference audibly in analog signals by ear if you know what to "hear for" but, obviously, the same cannot be said of a digital signal (unless the decoder is off - raw mode, which, in the GRE's case, would mean analog default and therefor simply operating in analog mode so it defeats the purpose).

Given his connections and the technical validity of past posts, I would tend to believe what Wayne_h is saying. Nevertheless, perhaps you are both right?

Consider, when the unit is in "Auto" mode it will default to whatever analog bandwidth mode is preprogrammed into it for the frequency it is currently tuned to. I believe we agree on this. If the unit is, however, set as FM then it will have that IF filter selected and, of course, if set as NFM it will have the NFM or narrower filter selected. Fine. We all agree here. Now, in ANY of these modes the scanner is "looking" for a possible digital signal (P25) UNLESS we have the channel set in CTCSS or DCS search (or set with a specific tone/code) mode. Therefor, in any of these modes it will START OUT in whatever bandwidth it is set for depending on the FM/NFM setting. Correct? Now, supposedly, in P25 NAC Search mode it should ONLY be looking for a P25 signal and ignore any analog signals (this is how I understand it). But, perhaps, even in this mode it is still INITIALLY using the analog bandwidth setting you programmed in (FM or NFM)? If so, then maybe we can account for SOFA_KING's data results by the action of the IF stage immediately BEFORE the device detects the P25 content. The IF BW setting may affect the receiver's ability to initially "hear" the signal after which the P25 detector and demodulator come into play. Since we can only see "hits" in the data and not quality analysis in terms of bit error rate, intersymbol interference, I/Q offset, etc., this may be the case. In other words, once the P25 detector has a positive track on a P25 signal it may indeed default to a set IF bandwidth filter, that being the standard FM filter as Wayne_h's source indicated, but just prior to that perhaps it was in whatever mode you set (FM or NFM)?

So the question is, does setting the unit to "P25 NAC Search" automatically switch in the FM BW IF filter or not. If it does (or is supposed to) then my theory is pfffft....but, well, it's just a thought.

Really, we can only really test it by doing a good adjacent channel interference test with the unit actively listening to a P25 signal of set level and watching the BER degradation with interferers at +/- specific frequency offsets (12.5KHz in the federal VHF ranges). Depending on the DSP magic being performed and where or what stage in the detection scheme, they may be using the analog FM filter rather than the NFM filter because the NFM filter may be too sharp and/or of otherwise too low quality for the P25 C4FM (and/or CQPSK) signal to accurately be decoded (at least with the quality of the filters used in this design) so they choose the wider filter and use only digital filtering down the line. Ideally, with well designed filters picked for the job (designed with the constraints of digital signals in mind - group delay, ripple, symmetry at band edges, etc.) this should not be required but in order to save costs with lower quality parts this may have been the necessary compromise. For analog FM the narrower filter may be fine but if not of sufficient quality it may be poor for digital signals (though I would think C4FM is one of the more forgiving digital modes as there is no major phase detection dependency as in modes such as CQPSK).

-Mike

 

[SOFA_KING]

Mike...Nice post, and I believe right on the money. I too wonder the same things as you. Is the filter a simple sine shape or is it a nice square shape? That is easy to test with a signal generator by sweeping the edges and taking SINAD readings. One would hope it is more square for data. We know what a sine shaped filter sounds like on analog when the deviation is pushed to the limit on a weak signal. It sounds distorted and degrades sensitivity by increasing distortion and noise. I will say that this scanner has very good adjacent channel selectivity...very good! A simple test around the WX channels shows that, but I never have much of a bleedover problem even on channels 12.5 kHz away. This is far better than my previous Uniden models.

The federal mandate is to go narrow, hence all of this new narrow band P25 stuff is coming on line, so the filter SHOULD BE narrow and not wide. Did GRE select the wrong filter for P25 because of a poor filter contour? (I have to say that weak analog signals sound fairly distortion free, so I think the design is fairly good.) Did they select the right narrow filter since this is supposed to be a narrow signal? (I need a little more to go on than "someone who would know". Would that be the design engineer for GRE???) Should GRE change the filter for P25, if indeed it is using the wide filter, to match the narrow transmission? Is there a problem with using the narrow filter on narrow P25? Was a decision made to default to a wide filter for P25???

A BER test in a controlled environment would be the best test method to prove this, but my real-world weak signal test was not such a bad approach. It does show something that is hard to debunk. The results are not speculation or "perception". Debunking them without any valid technical argument is. What was wrong with my test? (...and comments blindly blaming Win500 for bad test results are not valid. There is nothing wrong with Win500. I need a more technical argument than that speculation and "perception".) The test shows results, and that is much more that what Wayne shows.

I thought about the theory you presented that it may start off as NFM and then switch to FM after P25 signal detection, but the data suggest that is not where the big difference is as there is only about 6% more P25 locks on the NFM setting. The real difference is the 22% increase on NAC locks that were on the channel set for NFM. And if you park the scanner on a channel set as NFM with NAC Search, the display shows NFM...not DG. DG comes on after P25 is detected. Does the filter change at that point? If so, then why would I get better NAC decoding on NFM? Again, a P25 modulated signal generator would be a better test method, but some weak signal source testing is better than nothing.

One thing is for sure. It can't hurt to set the narrow band P25 channels to NFM, right? Even if it does switch back to the wider FM filter during NAC Search programming, you have nothing to loose however, if it actually does improve P25 reception, you have something to gain. I worry more about setting the actual NAC code on a channel as weak signals that lock P25 do not even decode the NAC at times. Would this mean the scanner would pass by a weak signal because it could not match the NAC in memory? Would staying in NAC Search mode hold the channel and increase you chances of getting something? Well it does do that in NAC Search mode! I keep it in NAC search for that reason. I'm not sure if having a NAC programmed in will hold on a weak P25 signal that the NAC has not been decoded on though. Even though this is supposed to be "the best digital decode" scanner, it takes S-2 or better to decode audio. That is a lot of signal! There is a lot of analog signal that can be quite clear to read below S-2. There is room for improvement on these GRE P25 scanners, so I'll take all the help I can get. The range on P25 is not as good as analog.

Statements like "Sometimes the placebo effect works well for people. :lol2:" are condescending and show a personal problem towards the OP. The test was not a "placebo". All of Wayne's statements on the subject show this bias, and none have any technical substance. His statements are void of any technical points and filled with empty speculation and a strange condescending nature. He can't explain why the test results are not valid. He depends on "someone" to support his disbelief of the test results. It appears to be a personal gripe more than a respectful technical discussion on an interesting topic. And this person is a moderator? How about a little respect, Wayne? If the only thing you have to debunk me with is what you have presented so far, you are not making a good argument. You appear to be out of your technical depth. Maybe it is defaulting to the wider FM filter (I'm open to that), but what technical reason is the test flawed and why do you have to be condescending towards me? Do you have something against me? If so, let's take it offline and work it out. I posted this experiment to help people get the best reception they can and because it was interesting, not argue a personal issue or grudge. OK?

Phil

 

[DaveNF2G]

It would also depend on what scanner you are using. Older scanners like the PRO-96/2096 will only decode P25 if set to FM mode. However, these scanners lack the NFM option. I only mention it to help anyone who might be confused by the discussion.

 

[Squad10]

Just after I received my PSR-500, I tried exactly what Phil addresses in this thread. Listening to P25 simplex portable and mobile transmissions in all three modes, I concluded that there was not enough of a difference (to my ear) to use anything other than auto.

Based on the 40 years I have been monitoring federal, my opinion is that P25 has lessened federal listening enjoyment due to its reduced simplex transmission range compared to analog. My last opinion is based on hobby equipment, not commercial 2-way.

 

[SOFA_KING]

Just after I received my PSR-500, I tried exactly what Phil addresses in this thread. Listening to P25 simplex portable and mobile transmissions in all three modes, I concluded that there was not enough of a difference (to my ear) to use anything other than auto.

Based on the 40 years I have been monitoring federal, my opinion is that P25 has lessened federal listening enjoyment due to its reduced simplex transmission range compared to analog. My last opinion is based on hobby equipment, not commercial 2-way.

It is a hard thing to test without the right equipment for sure. Oh well, as long as you are receiving something, that is good. I have Motorola P25 equipment and have compared weak analog to weak P25. I was shocked at how well the P25 did in weak signal conditions. But a GRE is not a Motorola. Too bad a Motorola can't scan 1700 channels.

Phil

 

[WayneH]

Phil, I'm not going to argue the topic with you. My comment about placebo effect was sarcasm. I'm sorry if you found it offensive.

And I'm not going to go in to further detail about who the someone is. If you don't want to believe me, don't. The technical details are out of the scope of my knowledge. I wanted a simple answer on the question, and I got one. If it's not enough, well, it's all I can give you for now.

 

[Mike_G_D]

Well, Phil, I don't think you're going to like this but I believe I have validated Wayne_h's "source" in terms of what the scanner selects for an IF filter in P25 mode. Yes, I am now convinced that the scanner does indeed select the standard FM filter regardless of the NFM/FM setting.

Here is what I did:

1) Pick a constantly broadcasting strong signal such as the NOAA weather broadcast in your area. In my area it is 162.400MHz.

2) Program a channel with a frequency offset above or below the strong broadcaster such that you can easily hear the quality of the distortion caused by the offset - you still want to be able to hear the signal but you want it to be off frequency enough to be distorted pretty badly using the standard FM IF filter setting. I used an offset of +6.25KHz so that I had a channel programmed as 162.40625MHz in FM mode. Note the S meter readout and the audio quality of the signal.

3) Program a second channel, ideally immediately adjacent to the first one to allow easy up/down arrow channel selection. Program this channel with the same frequency but using NFM mode. You should notice a significant difference in audio quality and S meter readout between this channel and the former due to the tighter IF filter being used. If is important that the S meter readout be indicative of this difference so if you cannot see a difference in S meter reading between the two then you need to pick a different offset which will show a difference in FM versus NFM mode. The reason for this will be obvious in the next step.

4) Program a third channel with the same frequency again using NFM mode and set the squelch mode to P25. Now note the S meter reading and see whether it looks like the first or second channel. Obviously, you cannot hear the audio in P25 mode as it is analog FM but you can still see the S meter reading - now you see the reason for noting the S meter reading in steps 2 and 3 above. Whichever S meter reading it most closely resembles (that of the first channel in FM mode or that of the second channel in NFM mode) will likely be the actual IF setting. In my case, it was completely obvious that in P25 mode the standard FM filter is being used and not the NFM filter.

To completely prove it to yourself you may want to check the results in a second experiment using the opposite offset. So, if in the first experiment you tried a + offset first then try the same experiment using a - offset. Be aware that there may be some asymmetry in the filters' response such that your opposite offset may have to be "tweaked" a bit to give you a good starting point and may not exactly match the first experiment's offset's absolute value. This is why, in my case, I ended up with a -11.25KHz offset rather than the ideal -6.25KHz offset for the second experiment. In my case, the results of the second experiment verified the results of the first. For whatever reason, the scanner is designed such that the standard FM IF filter is selected when in P25 mode regardless of the NFM/FM setting. I am firmly convinced as of now that the FM/NFM setting has no effect when the scanner is in P25 mode - the FM filter is selected either way.

Now, I am not sure why Phil got the results he did. I suspect it may have been due to the variability of the signals he was receiving versus time (quickly varying signal levels such that a null or peak or variations in between occur between the time stopped on one channel versus the time stopped on the next). I really do not know for sure. I might suggest some form of blind test wherein you program just as before but use the two adjacent channels in the SAME mode (FM or NFM) and see if the hits vary just as much as they did when each channel was programmed with different modes. If so, over a significant time period, then that may prove this theory. If not - I simply have no explanation at this time. I also believe I have sufficiently exploded my former theory concerning the explanation for Phil's data - that the unit is initially in NFM mode when that mode is slected before going to P25 - I think the above experiments prove that when P25 is selected the FM filter is selected right from the start. So that theory is now out the window, as it were.

For me, I, personally, am now sufficiently convinced of the validity of Wayne's "source's" information. I do not like it - I would like to be able to choose the filter I want regardless of mode, but there it is. I would also REALLY like to be able to search and tune in NFM mode!! Something I feel is a significant oversight on GRE's part - currently it will not allow you to select NFM mode in search or tune modes, only AM, FM, and AUTO. Ugggghh!!!

-Mike

 

[SOFA_KING]

Good work, Mike. It does not bother me at all that I was proven wrong. The test you did sounds reasonable. Thanks for doing it! I was wondering if there might have been a slight delay between the two channel scan that caused the NFM channel to be favored. I could try it again with channel 6 being FM and 7 being NFM, but what is the point if we know the P25 filter is forced to FM. Plus I have to wait for the band to open. I too wish GRE let you use the NFM filter for P25.

Case closed.

Phil