Avoiding co-channel interference when activating 2m FM

Calling all expert 2m FM Dx activators. I have a small operating procedure problem on which you might advise me.

I activated Helvellyn (G/LD-003) yesterday with a 5W HT and a RH770 ½-wave telescopic antenna and was pleased to get 21 contacts in 35 minutes on FM and C4FM, including a first for me – 2m contacts in GM, GW and G on the same activation.

The whole thing was marred slightly by a ragchew QSO that started up on the same frequency (145.475) after I had already had quite a few back-to-back QSOs. Although I had no problem hearing my chasers with this ++QRM at least three of my contacts told me they were having readability problems with my signal. So, I suspect there were some Dx chasers I didn’t work because they couldn’t hear me properly. I think this is a problem for very high summits in reach of dense populations (I rarely have this problem on lesser summits).

My usual procedure is to alert, spot and then call on the UK FM calling frequency (145.500). When a chaser calls me, I ask him/her to standby whilst I quickly check the 25kHz-spaced channels. I go back and tell the chaser which clear frequency I’ve found and we QSY. On the new frequency I announce my callsign and ask if the frequency is in use. If nothing heard after listening for a while, I call the chaser and ‘occupy’ the frequency for further QSOs.

No procedure is perfect and it’s probable that the ragchew stations couldn’t hear me.

I had QSY’d to a popular frequency (144.475). Would be the risk of QRM be lessened by choosing a less popular one (e.g. around 144.400) – I found many busy throughout the range - or use one of the ‘in between’ 12.5kHz-spaced frequencies?

Having spotted on that frequency I was reluctant to cause confusion by starting over to find another clear channel. Any suggestions?

73 Andy

++QRM (shorthand for co-channel interference – no slur intended on the other user)



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Andy Your procedure is good ! I heard you shout out on 500 then qsy etc and ask if the frequency was in use , and it was all clear. After about 5 mins some locals just came onto channel and just started rag chewing without checking availability first. I did break in to them and told them the frequency was in use for sota but they ignored me… So at least you are doing your job right. Shame though as I didn’t manage to get through to you.
best 73

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Without re-spotting I may have lost potential chasers who continued to listen on my now-vacated, spotted frequency. I had a pile-up most of the time and was reluctant to start messing with my phone again.

Maybe the solution is to find a clear frequency, announce the QSY, and ask someone to spot the new frequency for me.

Allen, thanks for trying and for asking the ragchewers to QSY. Next time maybe - I want to do High Street (G/LD-011) in the next week or so.
73, Andy

The co-channel interference should be even worse in narrower channel. Say 8 dB @12.5 kHz BW and 4 dB @ 25kHz BW.


If chasers are keen they will find you. It’s chasing, not shooting fish in a barrel. I think you are making hard work of a trivially simple thing that happens frequently.


Hi Andy, @G8CPZ,

Thanks for the difficult contact. In the clear when the man talking about his Dacia was quiet, I could hear you fine, but once he keyed up you were gone.

As Richard @G3CWI says, it’s a common issue. I’d generally QSY; in fact I was almost tempted to spot you and ask in the message text whether you could QSY, but wasn’t sure if that was acceptable or the done thing ha ha…:wink:

I’d suggest changing to a .*25 frequency, so those of us using old radios can still get you. Until my HTX-202 went pop last weekend and got replaced with something newer, I couldn’t get to the 12.5KHz frequencies. I think it’s similar on 4m with many older 25KHz stepped PMR radios in use.

Anyway, thanks again & hope to catch you soon.
Best 73, Simon


Would be the risk of QRM be lessened by choosing a less popular one (e.g. around 144.400) […]

No, the only difference is that you would be the jamming station.
144.150 - 144.400 CW/SSB
144.400 - 144.490 beacons


Hi Simon, thanks for the tip and the contact. I wouldn’t have seen your spot in time anyway. After I send my self-spotting SMS I don’t touch my phone again especially when on HF CW - I’m too busy listening/decoding/logging/stopping the log book from being blown away/swipping at midges [I was bitten all over yesterday] etc to look at the phone as well.

It’s a good job you blogged here cos I’ve got you logged as G7PKX not G7WKX [no wonder I couldn’t find that callsign on qrz.com]. I’ll edit my Excel log and resubmit it to the SOTA database.

73, Andy

Is it a valid contact if you get it wrong and then correct it later via the internet?

Maybe not. In any case I qualified the activation [with 18 other unique contacts] without my QSO with Simon so it’s just a question of what to do with the log already submitted. I’ve also read SOTA MT write on this reflector that it accepts logs submitted in good faith may contain [human] errors.

Richard, as a founder member of SOTA why don’t you tell me the answer to your question. I’ll delete the contact and resubmit the log if need be.

Hi Pom, thanks for pointing out my typo - yes of course I really meant 145.400.

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SOTA General Rules 3.7.1 refers. But more generally if you have to correct something as fundamental as a callsign over the internet, no proper contact took place (for any award or program).

I personally like to use 145.575 for FM. On one occasion have I had others jumping on the frequency whilst I used it. Politely asked most people will move on to another frequency, but you do have to let them tell each other that which does tie up the frequency for a while. To be honest I got a s2s on my last trip because an activator gave out a different frequency and ended up on mine as the chaser didn’t hear him correctly.

My personal practice is to alert on Sotawatch before I activate giving people notice. I then climb the hill, call on 145.500 but ask that anyone that wants to qso does qsy to my chosen frequency. I tend not to take callers on the calling channel. I then move, ask if the frequency is clear, then carry on. At that stage I spot myself as active on my active frequency. A lot of my callers know once the initial rush is over I’ll happily ragchew.

These are things which will always come up. It’s just how we deal with them that gets us remembered.

edited spot to alert to save on confusion

Do you mean alert? You spot when you are QRV and not before.

I usually use a portable yagi when activating on 2m. I have two Arrow brand 2m yagi antennas. One is the 4-element that disassembles and rolls up into a nice small package. The other is the 3-element.

By using a yagi instead of the omni 2m antenna from high above the surrounding population, you not only reduce interference from co-channel users, you also minimize causing interference to others.

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Yes I meant alert and that is what I do actually do. Sorry if it might of caused a bit of confusion to users.

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What I usually do is announce on the QRM’d frequency that I am going to find a new frequency and call CQ on the calling channel when I have found somewhere else to go. The pile up will follow you. I find this more reliable than trying to directly organise a QSY with chasers who might not be reading you well.

Just clone your previous spot with the new frequency if you have cellular data signal on http://sotl.as or hope that some kind soul spots you on the new one. Never spot on a frequency before you’re actually using it or sods law will come in to effect. Below 145.300 can be a good place to seek refuge if it’s busy.

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