Re: FDM DUO INCREDIBLY NOISY!!! #fdm-duo

Neil Smith G4DBN
 

Hi Tom, I live 50km from Emley Moor, and on some bands, the digital TV mixes with cellphone signals from 3km away to make wideband hash which I can only remove by adding very sharp filters.  OK, not on HF, but on there I can't hear much because of VDSL.

Does enabling and disabling the 50MHz low pass filter make any difference?  I had strong medium wave signals nearby, so I fitted an auto-switch filter to my DUO on HF and that removed the crud.  I was seeing a lot of that PK indicator though. Connecting a DUO to a wideband antenna in a high-RF environment is never a great idea, but if the 50MHz LPF makes no difference and the PK indicator is not showing, and if adding more attenuation drops the signal the same amount as the noise, then you are not suffering from overload.

Compare a VERY weak signal on the other radios and the DUO and see if the DUO can hear as well.  You need a signal that is right down at the limit of audibility, ideally a simple tone or CW.  I just hook up my signal generator and put a -130dBm pulsed signal into the antenna as a comparison, then drop the level until I can't hear the pulsing.  It is a bit of a pointless test really, as band noise is way higher than the noise floor of the DUO, but it is a good comparison.  I could be cheeky and say the other radios are deaf of course, that woudl make them quiet!

Try the ultra-weak signal comparison and see what the difference is.

Neil G4DBN

On 07/11/2019 08:57, Thomas McQuiggan wrote:
Yes, I live 1 mile away from WINTER HILL transmitter, but it causes me no problems on any other radio.

I ripped out the shack last night to have a big tidy-up, so when it's all back together, I'll do some side-byside comparisons with my IC-7400 and see what happens. The radio is already much better after adjusting the AGC Threshold.

Thanks guys,

Tom - M7MCQ
-- 
Neil
<a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>

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