[R-390] IF Transformer, alignment and performance

[Alan Victor]

So Tisha,

As a bench level data point for the receiver system you describe, what is
your ON BENCH 50 ohm signal level sensitivity measure? I assume for the
same S/N ratio you address hooked up to your receive antenna (nice), that
it is in excess of -112 dBm?

Thanks, Alan W4AMV


On Wed, Apr 10, 2019 at 1:20 PM Tisha Hayes <tisha.hayes at gmail.com> wrote:

> I have been lurking for quite a while, I continue to travel extensively and
> rarely get to fire up my radios;
>
> But on to sensitivity;
>
> We know what S/N (signal to noise ratio) and receiver selectivity has
> probably even more to do with receiver performance than just sensitivity,
> expressed as either RSL in dBm, uV or S-units.
> Once you get to the point where you are between 3 and 0.5 uV sensitivity
> and you are still wanting more you find yourself chasing after ways to
> improve selectivity.
> I did a few things to improve selectivity; since I was not worried about
> ESSB or wideband audio quality for BCB or SWL listening (I primarily listen
> to SSB or CW) I went after the stagger-tuning on the IF
> Going with a conventional alignment of the stages instead of an offset made
> the radio more selective. Building a 12 KHz wide roofing filter between the
> RF and IF decks helped as well.
> Fortunately I live in a radio-quiet area where across most bands the
> background noise levels are -110 to -115 dBm (S2-S3) when there aren't
> thunderstorm crashes I can dig out some good ones off of the tail end of a
> 1600' beverage.
>
> Trying to do better than -110 to -112 dBm RSSI required the use of a
> Faraday cage and constantly swapping good tubes for good tubes to find the
> quietest one. It reverted to black-magic and I wanted to do blood
> sacrifices and scatter chicken bones for better results. That is when I put
> a stop to that fools-pursuit.
>
> *Ms. Tisha Hayes, AA4HA*
>
> *Senior Engineer, 4RF*
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