Topband: W7IUV Preamp from Low Band DXing

[Tom Rauch]

> All my Rx antennas hear noise, so I conclude that they do 
> not establish the
> noise floor.  And the longest run of coax is low loss and 
> <500'.  So maybe
> what I should build is a multiple attentuator and 
> incorporate a relay
> switching arrangement to balance all the Rx antennas to 
> the same level on a
> quiet night.  Hmmm...  The wheels are turning.

You'll just have to look at signal levels. Knowing your 
radio I'd try to match the level required to use the radio 
without internal attenuation and with the IPO off.

> With respect to the attenuator topology, a simple 
> resistive PI circuit could
> be used to maintain Z while inserting some loss.  Is this 
> the approach to
> use?

W7IUV had a great suggestion, do a 75 ohm system and use 
CATV attenuators. Of course a 75 ohm attenuator will work 
fine even in a 50 ohm system..it will just have a small 
error in attenuation. When I need receiving pads, that's 
what I use. Of course my system mostly uses F connectors.

>Or can a fella use bias on some Pin Diodes to throttle the 
>signal
> output?

I'd stay away from that. The diodes need a very long carrier 
lifetime for 160 and probably special circuit topology. Keep 
things simple.

73 Tom