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High levels of QRM / QRN (3 replies)

M7HUG
2 weeks ago
M7HUG 2 weeks ago

Dear All,

I am newly licenced with thanks to Essex Ham, but need some advice please.

I have an FT-818nd which seems to suffer from huge amounts of QRM, often S8 / S9, across all bands (mainly trying 40, 20 & 17m)

I have attempted to isolate this by initially switching everything off at the mains in the shack (which isn't located in the house), and using the internal batteries - to no effect - I have turned the mains power of in my house, still nothing.

I have tried using a random longwire, a dipole and an end fed antenna, all with the same effect, everything is earthed to a 4 ft deep solid copper earthing point with I installed just outside of the shack.

 

My location isn't to crowed with other houses (see attached image), with the nearest o/head power lines a good distance from the shack.

I have taken the radio out into the field (SOTA location G/SE-001 Walbury Hill) where using a SOTA band hopper I get QRM at S0 to S3 - I have also tried the SOTA band hopper at home - again S8+

I am starting to get frustrated and a fear that I'll be spending a lot of time perched on top of a hill.

Would I find a vertical better that a horizontal?

What can I do to reduce QRM?

https://www.essexham.co.uk/images/FireShot-Capture-012-Google-Maps-www.google.co_.uk_.png
Peter M0PWX (2E0PWX)
2 weeks ago

Hi M7HUG

great news and congrats on passing your foundation (pete M0PSX is a great tutor)

several ways to find QRM, best is a small battery mw/sw radio reciever, and wander round the house and see where it gets worse, moving near equipment you will get an idea of what is giving off RFI / QRM

usual suspects are LED lighting, Solar panel invertors, powerline ethernet adapters, cheap phone chargers (switch mode PSUs), plasma TV's etc

think if there are any patterns to good / bad times which may help narrow down the search (all time, likely a PSU or something on standby all time, worse in the evening as it gets dark LED lights, dawn til dusk solar panel invertors as they need sunlight on the panels)

balanced antennas like dipoles tend to be quieter then long wire or off center fed dipoles

80m suffers as lot with QRM from BT DSL lines to houses

you can also find if you have a good antenna you need to reduce the RF gain or even enable the attenuator (if your rig has one) on HF bands

hopefully that gives you a few ideas to start the hunt for the source of your issues,  

Peter

M0PWX

M7HUG
2 weeks ago
M7HUG 2 weeks ago

Hi Peter,

Thank you for the pointers, having turned off all mains power to my property I had hoped that I'd be able to prove if the RFI / QRM was down to me, with everything off its still the same.

The only thing I can't do is isolate to DSL inbound, however this is routed to the house from the opposite side to where the shack is.

I will certainly try the trick with an old MW radio and see what I can find, and I'll also invest in a dipole, hopefully soon I will be on the air.... If not Walbury Hill will be my second home....

Peter M0PWX (2E0PWX)
2 weeks ago

DSL noise will normally only affect 80m band, so unlikely to be you main issue

if you have shut all power down to your house i think its fair to say the QRM is likely outside of your control

so try turning off the AGC (you will lose the S meter as FT-818 uses the AGC voltage for the S meter), backing of the RF gain, and try the attenuator, to reduce the noise, and see if you find any signals popping out the background,

one thing i have learnt in my 10 months of operating (i did 4 months RX only before i passed foundation with pete) RF gain etc can be counter intuitive, less is more often, if you back off the gain you don't amplify the noise so it drown the signals, its finding the sweet spot, enough gain to hear the signal, but not enough to bring the background noise up to much and you will find the sweet spot often varies by band

find a medium signal and gradually back off the RF gain , and listen does the signal become clearer as you do, but listen there will be a point where the signal starts to degrade, if you hit the minimum gain and things are still improving, engage the attenuator and adjust the RF gain again, My xiegu G90 the RF gain sweet spot is about 15-40%, my FT-991a its about 65-80%, when band conditions are good the G90 i have to put the attenuator in, the FT-991a RF gain drops nearer to 50%

give it a go, you only have a bit of time to lose, may be get a few grey hairs

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