QRM on Olycom 3

[Guest Puget Sounder]

I'm waiting for the FCC to issue my GMRS call sign. Submitted and paid Sunday 02/11.

A little backgound about me. I've been into radio monitoring for decades. I have never transmitted on anything except CB and  FRS. I currently have a Sangean 909x to pick up UHF, (30MHxz and below). I use a mla-30 active loop with a splitter to feed both my Sangean and RTL-SR for UHF. For VHF and UHF, I have a Tram 1411 Discone antenna that feeds a second SDR for monitoring that spectrum. I also own 2 GM 15 Pro HT's.

For the last few days, I've been picking up QRM from the Olycom 3 repeater (East Tiger Mt) from my station. This only happens  when people are transmitting on channel 18-(462.625.00) through the repeater. After their tail squelch, I can see on the waterfall and there is no signal on the frequency. -Totally quiet. People are speculating that it is purposefull interference or solar cycle. I don't agree.

Looking at the spectrum, I see that there is a constant diesel signal at 463.413.000. This signal from my location is a strong 35db above the noise floor. The signal is constant. Furthermore, at 462.738.000 there is a mirror signal (although at -10db) leading me to speculate that it may be a harmonic from the stronger signal. Going to frequency mode and punching these in will produce the sound that people are reporting.

Because some transmissions are coming in clear without the "Dieseling" I'm ruling out the repeater as a the source. In my humble opinion, the people with the worst noise are closer to the source. From my observation, it seems to concentrate around the SR 167 corridor and I-5.

My theory is that the strong spurious signal is being picked up by the users antenna (only a few MHz difference) and being re-transmitted to the repeater. FYI: the repeater CW ID is clean.

One other note: From my understanding, GMRS frequency allocation is 462-467 MHz. The only authorized transmissions are analog FM.

Comments?

[WRWE456]

Hello and welcome!

I am up in the San Juan Islands and I hear the Tiger Mt. repeater very well. Where are you located?

I don't have anything to add to your theory but it sound plausible. I had to look up QRM (man made interference from electronic devices)

as opposed to QRN (interference from natural source's) Very interesting stuff!

I don't know how many are using SDR's to monitor GMRS but we do have a few ham's around here that may have something to offer.

Thanks for sharing something new and interesting.

[SteveShannon]

8 hours ago, Guest Puget Sounder said:

One other note: From my understanding, GMRS frequency allocation is 462-467 MHz. The only authorized transmissions are analog FM.

Comments?

Not the entire range.  The FCC has identified four sets of specific channels. 30 in all on frequencies in the 462 MHz range and the 467 MHz range.  463-466 MHz are not GMRS.  We stay to those channels and we don’t get to twist our VFO knob and pick a clear frequency wherever we want.

Channels 15-22 are used for simplex communications, where people transmit directly to each other, taking turn transmitting and receiving on a single frequency.

If you add exactly 5 MHz to each of the 15-22 channels, you get the frequencies used for channels 23-30. So, 462.550 MHz becomes 467.550 MHz.

Channels 23-30 are used to transmit to a repeater.  Generally speaking that’s almost the only traffic on these channels: to the repeater.  Then, the repeater generally transmits on the corresponding channel in the 15-22 range.  So, channels 15-22 are shared between simplex communications and transmissions from repeaters.  The fact that these are shared and limited to these eight channels is one of the shortcomings of GMRS.

[Guest Puget Sounder]

47 minutes ago, Sshannon said:

Not the entire range.  The FCC has identified four sets of specific channels. 30 in all on frequencies in the 462 MHz range and the 467 MHz range.  463-466 MHz are not GMRS.  We stay to those channels and we don’t get to twist our VFO knob and pick a clear frequency wherever we want.

Channels 15-22 are used for simplex communications, where people transmit directly to each other, taking turn transmitting and receiving on a single frequency.

If you add exactly 5 MHz to each of the 15-22 channels, you get the frequencies used for channels 23-30. So, 462.550 MHz becomes 467.550 MHz.

Channels 23-30 are used to transmit to a repeater.  Generally speaking that’s almost the only traffic on these channels: to the repeater.  Then, the repeater generally transmits on the corresponding channel in the 15-22 range.  So, channels 15-22 are shared between simplex communications and transmissions from repeaters.  The fact that these are shared and limited to these eight channels is one of the shortcomings of GMRS.

Thanks for that. I understand that GMRS is channelized and I should have been clearer. I also omitted that CW is authorized. But I am not clear if any transmissions are authorized between the channels. 

I see that the issue is still persisting this morning . There was talk on the repeater yesterday that a team was going  to hunt down the issue with their passive radar (Kracken). I was hoping somebody would relay my findings because IMO they should concentrate on 463.413.000.

Anyone within range of OlyCom3 can verify  my findings by turning your radio to Frequency Mode and punching in 463.413.000 or 462.738.000. -Looks and sounds like constant DMR, but I'm no expert.

[SteveShannon]

1 hour ago, Guest Puget Sounder said:

Thanks for that. I understand that GMRS is channelized and I should have been clearer. I also omitted that CW is authorized. But I am not clear if any transmissions are authorized between the channels. 

I see that the issue is still persisting this morning . There was talk on the repeater yesterday that a team was going  to hunt down the issue with their passive radar (Kracken). I was hoping somebody would relay my findings because IMO they should concentrate on 463.413.000.

Anyone within range of OlyCom3 can verify  my findings by turning your radio to Frequency Mode and punching in 463.413.000 or 462.738.000. -Looks and sounds like constant DMR, but I'm no expert.

CW is not permitted.  Morse code is allowed when identifying, but it’s just tones on FM.

Transmissions are only allowed on the channels established by the FCC in part 95e.  Therefore they are not authorized between the channels. Neither of the frequencies you mentioned are approved for GMRS.

Also, users must observe the rules regarding bandwidth and power output.  I’ll paste the section that establishes the individual channels by frequency, but for the other limitations you should really visit the regulations.

https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-E

§ 95.1763 GMRS channels.

The GMRS is allotted 30 channels—16 main channels and 14 interstitial channels. GMRS stations may transmit on any of the channels as indicated below. 

(a) 462 MHz main channels. Only mobile, hand-held portable, repeater, base and fixed stations may transmit on these 8 channels. The channel center frequencies are: 462.5500, 462.5750, 462.6000, 462.6250, 462.6500, 462.6750, 462.7000, and 462.7250 MHz. 

(b) 462 MHz interstitial channels. Only mobile, hand-held portable and base stations may transmit on these 7 channels. The channel center frequencies are: 462.5625, 462.5875, 462.6125, 462.6375, 462.6625, 462.6875, and 462.7125 MHz. 

(c) 467 MHz main channels. Only mobile, hand-held portable, control and fixed stations may transmit on these 8 channels. Mobile, hand-held portable and control stations may transmit on these channels only when communicating through a repeater station or making brief test transmissions in accordance with § 95.319(c). The channel center frequencies are: 467.5500, 467.5750, 467.6000, 467.6250, 467.6500, 467.6750, 467.7000, and 467.7250 MHz. 

(d) 467 MHz interstitial channels. Only hand-held portable units may transmit on these 7 channels. The channel center frequencies are: 467.5625, 467.5875, 467.6125, 467.6375, 467.6625, 467.6875, and 467.7125 MHz.

[WRYZ926]

And those two frequencies are also outside of the 70cm amateur band. The 70cm band is 420.000 MHz to 450.000 MHz.

[WRWE456]

I heard a couple guys talking about it on the Tiger Mt. repeater this afternoon and said it seems to be cleared up today.

[Guest Puget Sounder]

3 hours ago, WRWE456 said:

I heard a couple guys talking about it on the Tiger Mt. repeater this afternoon and said it seems to be cleared up today.

Yes. Contacts are a lot cleaner today. I don't hear the interference anymore on people's transmit. I still stand by my theory that the noise was being picked up by the users antenna because there is no way any person could stop the interference at the exact same time before the tail squelch. After the tail squelch, the frequency was totally silent. At any rate, I don't have the tools here to go back in time and see what I was missing.

BTW, I appreciate you getting back to me on topic.

I did get my callsign e-mail from the FCC this morning. WSAT598. Jack from Yelm. I tried a signal check to the repeater and came in holding the repeater, but weak. I guess I'll have to shop for a better aftermarket antenna. I have two Abbree AR-771s which were bundled with my purchase of the GM15 Pros. I was hoping that they would be a significant upgrade from the stock antennas. Alas...

[WRWE456]

WSAT598 that's a cool call sign! That Tiger Mt. repeater really has some reach.

One thing to keep in mind with the whip antennas is to keep them vertical while transmitting. I believe that Abbree is a copy of the Nagoya NA-771G https://www.buytwowayradios.com/nagoya-na-771g.html?___SID=U which is a very good antenna. Is it as good as the Nagoya? I don't know. And of course getting outside and up high will help.

[WRYZ926]

I have a Nagoya 771G and a couple of the Abbree copies. I tested all three on my Comet antenna analyzer yesterday. The Abbree antennas have a lower SWR than the Nagoya. Granted that is only a sample of three antennas.

[SteveShannon]

1 hour ago, WRYZ926 said:

I have a Nagoya 771G and a couple of the Abbree copies. I tested all three on my Comet antenna analyzer yesterday. The Abbree antennas have a lower SWR than the Nagoya. Granted that is only a sample of three antennas.

What were the SWR values and did you measure at both the 462 and 467 MHz frequencies?

[WRYZ926]

I didn't write the numbers down. I did test at both 462 and 467. The Abbree antennas were around 1.2 while the Nagoya was around 1.7 IIRC. All were still below 2.0 but the Abbree antennas were better.

I also tested the factory Wouxun KG935G antenna and the SWR was around 2.0 on 462 and 467. The funny thing is that antenna works better on transmit and receive with the 935G than the Abbree or Nagoya antennas.

[PugetSounder]

28 minutes ago, WRYZ926 said:

I didn't write the numbers down. I did test at both 462 and 467. The Abbree antennas were around 1.2 while the Nagoya was around 1.7 IIRC. All were still below 2.0 but the Abbree antennas were better.

I also tested the factory Wouxun KG935G antenna and the SWR was around 2.0 on 462 and 467. The funny thing is that antenna works better on transmit and receive with the 935G than the Abbree or Nagoya antennas.

Thanks for that. I don't want to throw money at it just to be disappointed. The Abbrees did have good reviews.

I used the line of site website and there are no terrain issues between me and the repeater.

I wonder if my mic is the issue. I read somewhere where people gently drilled out the mic hole to open it up a bit?

I looked at some Comet analyzers and was wondering which one you have?

[dugcyn]

 

18 hours ago, Guest Puget Sounder said:

Yes. Contacts are a lot cleaner today. I don't hear the interference anymore on people's transmit. I still stand by my theory that the noise was being picked up by the users antenna because there is no way any person could stop the interference at the exact same time before the tail squelch. After the tail squelch, the frequency was totally silent. At any rate, I don't have the tools here to go back in time and see what I was missing.

BTW, I appreciate you getting back to me on topic.

I did get my callsign e-mail from the FCC this morning. WSAT598. Jack from Yelm. I tried a signal check to the repeater and came in holding the repeater, but weak. I guess I'll have to shop for a better aftermarket antenna. I have two Abbree AR-771s which were bundled with my purchase of the GM15 Pros. I was hoping that they would be a significant upgrade from the stock antennas. Alas...

both brand 771s seam to work well with my HT'S but yelm is a pretty far trip for them. dont know if you are willing or able to make it semi moble setup but a fairly inexpensive gmrs car-truck antenna or base antenna up high may get you many more fars. I have reached 22 miles simplex with my HT on 50 ft mast antenna. I know that is extreme but does show the difference.

welcome to GMRS hope to catch you sometime on tiger rptr.

Doug

[WRYZ926]

3 hours ago, PugetSounder said:

Thanks for that. I don't want to throw money at it just to be disappointed. The Abbrees did have good reviews.

I used the line of site website and there are no terrain issues between me and the repeater.

I wonder if my mic is the issue. I read somewhere where people gently drilled out the mic hole to open it up a bit?

I looked at some Comet analyzers and was wondering which one you have?

I have the Comet CA-500 MkII, with is the only one currently made by Comet. They aren't cheap. But if you plan on building your own antennas then they definitely are worth it.

Myself and others have mentioned that drilling the mic hole bigger on the Baofeng hand mics does help. Just don't go too big.

I also have a couple of Nagoya 771 dual band antennas for my UHF/VHF radios too. The Nagoya and Abbree antennas work better than the stock rubber ducks on my Baofeng and Explorer QRZ-1 (TYT UV-88). But I didn't notice any improvement over the stock rubber ducks on my Wouxun KG-935G and Icom IC-T10.

[PugetSounder]

3 hours ago, dugcyn said:

 

both brand 771s seam to work well with my HT'S but yelm is a pretty far trip for them. dont know if you are willing or able to make it semi moble setup but a fairly inexpensive gmrs car-truck antenna or base antenna up high may get you many more fars. I have reached 22 miles simplex with my HT on 50 ft mast antenna. I know that is extreme but does show the difference.

welcome to GMRS hope to catch you sometime on tiger rptr.

Doug

Yes. The repeater is 50+ miles from here. However I have heard someone walking their dog in Yelm and coming in clearly with their HT. Also someone in Tenino was booming with a handheld. Tenino is 15 miles further south, but they have some hilly areas vs Yelm which is fairly flat prairie land.

I have a large 10x30 metal RV carport near my shack. It's around 12' tall. I was thinking about putting a mag mount GMRS antenna on it and see what happens. That will = 4 antennas. Glad I'm not in an HOA.

I should mention that I have dual watch set to channel 18 and 26 so I can see if I'm picking up simplex or repeater. On occasion, I can even hear the repeaters CW on one of my Cobra FRS radios.

 

[SteveShannon]

2 hours ago, PugetSounder said:

I should mention that I have dual watch set to channel 18 and 26 so I can see if I'm picking up simplex or repeater.

How can you tell?  TSQL on 26 and no tones on 18?

[PugetSounder]

My radios show the active channel by way of an arrow? Don't they all when in Dual Watch?

[Hoppyjr]

If you’re hitting Tiger Mountain from Yelm that’s impressive. Oly3 and the OlyComm group are a good bunch of folks. Welcome to the party.

[PugetSounder]

On 2/14/2024 at 5:46 PM, Sshannon said:

How can you tell?  TSQL on 26 and no tones on 18?

Thank you Steve. You got me thinking... Maybe I should listen for the TSQL to be sure. Sure enough, I'm hearing TSQL on both channels (018 and 026). But the arrow will change at times. This led me to believe that the radio was able to distinguish between simplex and duplex. Now I'm not confident. Does anybody have an explanation for this or am I missing something?

[PugetSounder]

5 minutes ago, PugetSounder said:

Thank you Steve. You got me thinking... Maybe I should listen for the TSQL to be sure. Sure enough, I'm hearing TSQL on both channels (018 and 026). But the arrow will change at times. This led me to believe that the radio was able to distinguish between simplex and duplex. Now I'm not confident. Does anybody have an explanation for this or am I missing something?

I should also add that I can hear the repeater with my Cobra FRS radios for short periods. TSQL is also heard. Not routinely though. I'm assuming because of changes in propagation.

[SteveShannon]

57 minutes ago, PugetSounder said:

Thank you Steve. You got me thinking... Maybe I should listen for the TSQL to be sure. Sure enough, I'm hearing TSQL on both channels (018 and 026). But the arrow will change at times. This led me to believe that the radio was able to distinguish between simplex and duplex. Now I'm not confident. Does anybody have an explanation for this or am I missing something?

I suspect your receiver is listening on both channels (18 and 26).  If it’s a dual VFO receiver the two VFO’s are sequentially polled at a brisk rate. If your radio is on 18 when the signal is detected it identifies the signal as being on 18.  If it’s on the other VFO at the time it identifies it as 26, but in reality unless you know two different transmitters use different tones or transmit signals with different characteristics, like a Roger beep on one or ANI on one, it’s probably not possible to distinguish. 

[PugetSounder]

11 hours ago, Sshannon said:

I suspect your receiver is listening on both channels (18 and 26).  If it’s a dual VFO receiver the two VFO’s are sequentially polled at a brisk rate. If your radio is on 18 when the signal is detected it identifies the signal as being on 18.  If it’s on the other VFO at the time it identifies it as 26, but in reality unless you know two different transmitters use different tones or transmit signals with different characteristics, like a Roger beep on one or ANI on one, it’s probably not possible to distinguish. 

That makes sense. So I've been dual watching (scanning) two different channels on the same frequency and it's just burning battery faster without any appreciable benefit.

[SteveShannon]

18 minutes ago, PugetSounder said:

That makes sense. So I've been dual watching (scanning) two different channels on the same frequency and it's just burning battery faster without any appreciable benefit.

I don’t know that it makes any difference to battery life, but there is no appreciable benefit. Now if you filtered on different tones for the two different channels it would make a difference. For instance, if you know that the repeater uses 100 Hz as it’s CTCSS output tone you might want to program that tone into 26.

If you discovered that there were people transmitting on 18 using 143.3 Hz and you set that tone for 18 then you could tell which is which, usually.

[PugetSounder]

19 minutes ago, Sshannon said:

I don’t know that it makes any difference to battery life, but there is no appreciable benefit. Now if you filtered on different tones for the two different channels it would make a difference. For instance, if you know that the repeater uses 100 Hz as it’s CTCSS output tone you might want to program that tone into 26.

If you discovered that there were people transmitting on 18 using 143.3 Hz and you set that tone for 18 then you could tell which is which, usually.

I don't know either, but I was just speculating that the radio briskly polling between the two would result in a bit larger draw as opposed to just monitoring a single channel.