[TenTec] Argosy RF attenuator mod

[wa3fiy at radioadv.com]

On 26 Sep 2007 at 15:21, Kevin Purcell wrote:

> Adding an attenuator to the Argosy is perhaps one of the best things  
> you can do.
> 
> The RF amp is always in circuit in the Argosy in front of the mixer  
> which for the low bands is just not needed. The noise figure of the  
> antenna is much higher than the noise figure of the front end. But  
> due to some cunning design the RF amp is reused as a post-mixer  
> driver in the transmit chain so it's difficult just to take out of  
> circuit.
> 
> The nice feature of the 1980s TT rigs is they're separate boards  
> linked together at 50ohms so it's easy to grab a signal and  
> manipulate it rather than hacking on a PCB track.
> 
> There is a nice rx only link from the LPF board to the Mixer board  
> that you can use install a attenuator.
> 
> WA3IFY, how did you add yours?
> 
 
> 73 Kevin
> 
I've tried several different approaches and have settled on switching a 
resistive pi type attenuator with a really tiny dry circuit DPDT relay.  It simply 
inserts in series with the coax cable that runs from the LPF/SWR board to 
the first mixer board.  Very easy to do.  I switch it with the power on/off 
switch of the volume control.  ( after I remove the 120 volt wiring of course !)

The mixer end of the circuit is connector #33.  I build a very small circuit 
board, roughly the size of a postage stamp, and use MTA connectors just 
like TT uses in the Argosy.  Makes it a snap to remove or do other service 
on the radio if need be.  I've never had occasion to remove it though.

73,

-Lee-




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