FM Repeater Over Deviation / Clipping

K2BKD · July 14

Hello,

I am running a Flex 8600 with a Q5 signals 2m transverter. I am having a clipping issue on my club's repeater. There does not seem to be an audio setting that stops the issue. While trying to resolve this with a couple friends from my club another gentleman from the area joined the conversation (he seemed very knowledgeable on this matter). Suggested that I was likely over deviating and if I could get my frequency deviation under 3k I should be ok. I was using NFM so I should have been 2.5k or less. He seemed to think i was over that. Has anyone else had experience with this? I read the post "2M Repeater Question" That situation sounded similar. I don't know if there was a resolution. Thanks in advance for any advice.

Rich
K2BKD

Mike-VA3MW · July 17

I ran some tests on 146.520 and monitored the Deviation on an IFR-1200s.

With radio in FM (not NFM), LPF cut set to 2850Hz and Mic Level not quite hitting 0dBm, the deviation is 5KHz which is exactly where you want it for FM work.

As Ken says, if you overdrive the Mic line and/or you increase the High Cut audio, you can and will overdeviate the transmitter.

If you are clipping, I suspect your LEVEL is too high (Mic Gain). Keep an eye on that.

I create a Mic Profile for my KOSS headset called Koss FM. If you set up a slice on 2M FM to your repeater frequency, pick the FM Mic profile that you create and then save it as a Global Profile then the next time you want to go to your Repeater Freqency, just load the Repeater Global Profile you created and it will recall all the settings as they were saved.

73

Mike-VA3MW · July 14

2M FM deviation Max is 5Khz.

K2BKD · July 14

Shouldn't NFM get me down to 2.5 Khz? Apparently, this repeater is more sensitive to the deviation than some others. This was actually the first suggestion from my friend that runs our clubs nets. He is also a Flex user and using NFM normally solves the problem. A big part of my reason for buying the Q5 transverter was to have a reliable way to remote into my radio and do my clubs net 2x a week. I am really hoping to find a way to eliminate this clipping issue so that I can do that.
Thank you, Mike.

Stan VA7NF · July 14

Deviation is a mix of modulation frequency range and modulation level. Just as a test try reducing your audio upper limit.

You mentioned there was another flex involved - Have it inspect your transmitted signal with a greatly expanded panadapter. If it is not too wide then it is your audio content and level. Transverter distortion is a very low possibility.

Have the other flex inspect yours's and other's signals.

Geoff AB6BT · July 14

Here's a handy rule that accounts for most of the energy in an FM signal:

Mike-VA3MW · July 14

Hi

It sounds like the problem is the repeater. :) I would be really surprised if that repeater was set up for sliver deviation. You might want to ask the repeater owner.

I've worked on amateur repeaters for decades and generally, if you send a touch tone of #3 it is supposed to be 3Khz if I remember correctly. @David Decoons, wo2x can keep me honest on that one. But, you need a deviation monitor to correctly check. Or, even talking into it.

Beyond that, I would recommend that you keep an eye on the Mic level and make sure you are not overdriving that Level meter when in TX. If you overdrive that, you will cause clipping. As well, make sure that your LPF for the MIC is set to about 3000hz or less.

Give those a try.

John KB4DU · July 15

Geoff, just for clarification for me, what is “most of the energy” in the signal?

Geoff AB6BT · July 15

John, This is from Wikipedia but there are other references as well:

John KB4DU · July 16

Got it! Thanks!

Ken Wells · July 17

Be especially careful of your TX Bandwidth settings (Low-Cut and High-Cut)
I would recommend using something like 300-3000 or 300-2700.
Using Low-Cut of 300 keeps mic audio out of the CTCSS range.
Keeping High-Cut at 3000 or below limits ultimate bandwidth.

You might use PROC on NORM only. Or NONE at all. Never use DX or DX+ for FM)

Be very careful not to use a lot of TX EQ - don't use as much treble boost as you might normally use for SSB.

Be careful with the Mic Gain - keep the Mic LEVEL meter so that it peaks only between -10 and -5 on the LEVEL Meter.

If you still are over-deviating this repeater, try using FMN mode.

See this article and the links within it for more information.

Adjusting your Microphone Settings for Best TX Audio – FlexRadio

KD0RC · July 17

Another thing to consider - are you on frequency? It can sound like over deviation when you are off frequency.

K2BKD · August 4

Huge thank you to everyone for your help! Sorry for the delay in response. Between a 10-month-old human baby and a 13 year old German Shepard having a second knee surgically repaired, the back half of July got a little crazy on me. I didn't have a lot of time to allocate to figuring out the solution to this issue. So again, I do apricate everyone taking their time to join in and help me with this! Mike, you nailed it. Yes, while I mostly use my club's older Motorola repeater. It does seem to be the only one I have tried that is quite as sensitive to this. While I have not really had the chance to dial in where the boundaries are, and I will try the 350 low cut and 2850 high cut settings you showed. I changed the settings from the default which I know was 2900 on the hi cut (LPF) to 2750 and have the low cut set to 250. This has eliminated the clipping. I will try this on regular FM vs NFM I suspect that it will work as suggested. Yes, I am being very cognizant of not over driving my mic an have the AGC meter active all the time to see where I am. I think we have found the solution for me. I really apricate all of the help! Hopefully if anyone else in the community runs into this issue this helps them as well.

Thank You All!

Rich - K2BKD

FM Repeater Over Deviation / Clipping

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