[CQ-Contest] Pre tuned Hf amps

Jack Brindle jackbrindle at earthlink.net
Sun Sep 24 16:51:34 EDT 2006

Actually, the SWR bridge would need to be on the output of each  
amplifier. The TX should see a relatively flat, very good SWR looking  
into each amplifier. It is the antenna impedance that will vary, and  
it is the amplifiers that see it and will suffer from it. You could  
throttle back TX power based on the match (or lack thereof).

On the lower bands, notably 160m and 80m, antennas tend to change  
impedances rather rapidly for a frequency change. These two bands  
benefit the most from an ATU, and will suffer the most with a broad- 
band amplifier using only low-pass filters. You'd better have the SWR  
fold-back circuitry in place for these, because they are going to  
need it.

It may cost less to have five (or more) separate amplifiers, but the  
extra features built into the more expensive amplifiers, notably the  
ATUs, make them far more versatile than individual amps.

On Sep 24, 2006, at 12:24 PM, Ed wrote:
> And the answer to his quedstion is to use an antenna switch to route
> the drive to the amplifier he wants. As for protection, a single SWR
> bridge at the rig will do that job, although personally, I would build
> one which had the ability to immediately shut down the Tx, IF the SWR
> exceeded a certain limit. Most Txs have the capability to reduce power
> drastically as a function of SWR, but in this case, I think I might
> work on a "lockout".
> 73
> Ed

- Jack Brindle, W6FB

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