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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