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 QRM eliminator.

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Chickenfoot@1987
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Chickenfoot@1987


Call Sign : 26-CT-4029
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Equipment Used : CRT 9900,6900N,xenon. 3 element yagi,Sigma Eurocomm AmPro and other bits and pieces

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PostSubject: QRM eliminator.   QRM eliminator. Icon_minitimeThu Nov 11, 2021 2:56 pm

Hi everyone,As you may have noticed I’ve complained about that QRM I suffer from on 2-3 channels on the Mid block.Channels 13,14 and 15 are sometimes unusable with S7 of noise at times and as you can tell I’ve tolerated enough.So watching numerous YouTube videos and read comments on this forum I’m buying a QRM eliminator to rid the dreaded noise..(hopefully)
I get the principle with Main antenna and Aux antenna and phasing between the 2 and hopefully eradicating the unwanted noise.What I’m unsure of is the PTT connection,The one I’m buying says it has a built in PPT control but Looking at the rear of the device I can clearly see a PTT socket.
So how would/should I use this and how does my radio connect to this PTT control at the back.I’m using a SS9900 and on this radio at the rear is just an extension speaker plug and nothing else.
All help is great appreciated.
Thank you Tom.
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SangueG
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PostSubject: Re: QRM eliminator.   QRM eliminator. Icon_minitimeThu Nov 11, 2021 7:06 pm

Tom, I looked into these previously. I never went ahead with a purchase as my unwanted noise subsided as I made other changes. But what I did learn is that many of these units have an inbuilt PTT control, in that when you key up it switches the aux antenna out of the loop and when you de-key it switches it back in...

This apparently is fine and works well on AM/FM, but for SSB not so.. with the output power continuously fluctuating the switching doesn't work well. That's what the PTT connection is for, for the radio to signal the unit to switch in and out of line. Many Ham radios have ports on them for this, but for the main the 10/11m radios don't.

I couldn't see any easy way to connect to my 6900. If I had gone ahead I would have had to turn it on and off each time transmitting on SSB, or connect a switch, maybe on a foot pedal like some people do for large amps, which is still a manual operation of course.

I did see one video once, can't find it now, where someone gutted an old Zetagi preamp and used the automatic switching circuitry in it to operate the QRM Eliminator effectively. Apparently Zetagi mastered this auto switching well. Might be an option, but I guess try it manually first to see if it does work for you. Good luck.

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Chickenfoot@1987
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Chickenfoot@1987


Call Sign : 26-CT-4029
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Equipment Used : CRT 9900,6900N,xenon. 3 element yagi,Sigma Eurocomm AmPro and other bits and pieces

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PostSubject: Re: QRM eliminator.   QRM eliminator. Icon_minitimeThu Nov 11, 2021 7:37 pm

Thanks SangueG for explaining the QRM eliminator set up,Makes perfect sense now and it’s a shame about the switching on the PTT and SSB.As you know the CRT radios don’t have that port on the rear so that scuppers that idea.
I knew I should have bought a Yaesu or Icom now..lol
Joking aside I did see that person do the Zetagi preamp mod on his QRM eliminator but I’m far from skilled enough to attempt that sort of thing and those bare wires put me off from trying.Thanks again SangueG for the advice and has anyone else got around this problem with the SSB modulation and using a QRM eliminator?
Cheers Tom.
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Victor
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PostSubject: Re: QRM eliminator.   QRM eliminator. Icon_minitimeFri Nov 12, 2021 9:16 am

Hi Tom,

As Neal has already pointed out and you've discovered there are problems associated with the PTT control on typical QRM eliminator units. There are commercial 'auto RF sensing antenna switch' switches available on the market, (pretty pricey!), and they don't always work as well as advertised. The 'homebrew' solutions may or may not work and dependant on your abilities to construct such items.

To be honest I had in the past constructed a couple of circuits for QRM 'eliminators' and was left less than impressed with them despite much experimentation and a plethora of 'noise antennas'. They had a similar performance to an old Australian idea of hooking up a 'noise antenna' via an ATU and T-piece to your transceiver and a PTT antenna switching unit. (Totally passive, no powered electronics).

Some people swear by them as can be seen on some videos but others rate them very poorly.


My greatest results to resolving QRM woes was by checking into common-mode problems and a simple 1:1 common mode choke on my dipole array. Whereas before simple things like the bathroom extractor turning on would obliterate my whole HF reception I now have no problems at all. The aforementioned homebrew QRM circuitry would achieve similar results but with a lot of faffing about 'tuning' the damn thing and then only reducing the extractor electrical noise but not much else. (Such as nearby farm power lines which spew RF interference the moment it rains!)

I had already thought about removing said extractor before even going as far as fitting ferrite toroids to it's power lines to no avail but I could hardly tear down the farmers power lines. Wink

I still have an inkling that these QRM eliminators work mostly by 'isolating' your antenna line more than anything else.


Many times I've mentioned chasing the proverbial 'dogs tail' simply because I've been there myself!


There is always much talk about ground loops, earthing everything and such but to me that does feel like a bit like putting a bucket under a leak in a roof and if it overflows put a bigger bucket there or an overflow system. Better to fix the damn leak first.

The nice thing about my 1:1 CMC choke solution was it was easy to implement.....and doesn't require a PTT control. Smile


I wish you the best with it all Tom and if it helps any here's a little video that I came across some time back with a bit of insight :-

https://www.youtube.com/watch?v=P6gjn2sCCJM


All the best,
Victor

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Chickenfoot@1987
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Call Sign : 26-CT-4029
Posts : 377
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Join date : 2021-03-06
QTH or Location : London
Equipment Used : CRT 9900,6900N,xenon. 3 element yagi,Sigma Eurocomm AmPro and other bits and pieces

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PostSubject: Re: QRM eliminator.   QRM eliminator. Icon_minitimeFri Nov 12, 2021 9:46 am

Good morning Victor,Thanks again for that great answer on my QRM problem.The strange thing is that this QRM is very narrow on the band and only spans across 3 channels (only),I did what you advised me in the past about making a common mode choke and prior to the problem I have now and this only started about 2-3 months ago.I had S2 of noise on a bad day and all seemed fantastic as with the RF gain half open you would have thought the volume was turned right down is was that quicker.
I’ve even resorted to switching off the whole house power supply and running the radio straight from a car battery but sadly the problem on those 3 channels remained.We have not bought any new electrical items and all the existing ones have had a clam type ferrite ring fitted around their cables.So I can assume 99% the QRM is not from our property.I know it’s 3 channels and I read people have just learnt to live with it,but what happens when 3 becomes 20 or even worse and the monty and effort we put into this fantastic hobby why should I have too.I’ll look into that RF sensing switch and watch that video you advice Victor and see what else I can learn about the QRM eliminator,I did actually see another YouTuber who lives in a shed (sorry Fred) as he was using one on a ss 6900n but sadly he didn’t show how he got around the connection.
Thanks again Victor for the sound advice and I’ll be schooling up on the subject this weekend as if all else fails the kids can pack their bags were moving.😂
Cheers Tom.
26 CT 4029

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