[Premium-Rx] Preamp advice..

[Ahmet Gundes]

Hello Dan,

I would check two things to see if the Preamp ( of any kind ) works
in your application:

1. Make sure that the Preamp Input and Output Impedances ( usually
50 Ohms ) is matching the Input and Output devices. In this case your
Output unit is the Racal 6790 which should have a 50 Ohm impedance
as it is std in these rcvrs ( I don't have the 6790 but they are usually all

same, industry std 50 Ohms ).
Your input ( Antenna I presume ) should be the same as the one you
are using for R7 so that the same conditions are valid for both receivers.

2. Another point is to measure the Preamp and its effects with the Receiver
AGC OFF.  This is important as the AGC will stabilize any changes in Gain.
Some Receivers do have a real time Signal Indicator ( RSSI ) which works
without the AGC ON and it is useful in many cases to see sudden changes
in signal strength.  I do not know how this works on the 6790. Harris
590A will NOT show the Signal Strength if the AGC is out. Some other
receivers will.

Besides I personally don't think there is anything trivial to connecting a
Preamp
to any system like yours. It should work fine. I got a feeling it is the AGC

that needs to be turned off in order to see the effects.

Good luck.
Ahmet / kc2haa

** What is the model # of the WJ HF Preamp ? Do you have picture of it ?



Dan Neves wrote:

>         Hello everyone:
>
>         I am new to the list, but have a little quandary.. I am using a
> WJ HF preamp with an R7. Both the R7 and WJ preamp are powered from the
> same 12V battery.
>
>         The R7 has enough of a preamp already, however with the internal
> preamp switched out the WJ delivers about the same gain and noise figure
> as the internal unit.
>
>         The challenge is to get this preamp to work with the RACAL
> 6790GM. The preamp shows no volume gain in the signal. I have tried
> grounding the receiver to the   preamp chassis as well as to the - power
> lead. Also, grounding coax lead-in BNC shell to these same ..no change.
> WJ preamp will go to 20V..12 works fine w/R7.
>
>         This preamp has BNC in/out connectors + and - power leads and
> chassis ground. Does anyone have a suggestion as to what to try next?
>
>         Cordially Dan7R7
>
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