W8JI wrote:
>
>ALC will not cure the problem, because ALC is traditionally too slow
>to limit leading edges of waveforms.
>
>Also be sure the radio actually keys the PA before RF is applied, and
>removes RF before the keying signal is removed. I've seen radios
>output RF long after the PA is unkeyed!
>
As a side-issue, has anybody experimented with TX/RX sequencing that
sends a TX inhibit signal back to the exciter ALC input?
The sequence would be something like this.
RX>>>TX:
1. RX state: PA is unkeyed, and is sending a negative TX-inhibit voltage
to exciter ALC input
2. Exciter keys PA: TX inhibit voltage maintained while PA antenna
relays are changing over.
3. PA antenna relays switched and settled: PA removes inhibit voltage
from ALC line and exciter can now deliver RF. (Normal ALC operation is
now possible if desired.)
TX>>>RX:
1. TX unkeys PA, but PA antenna relays hold in. PA is quickly biased to
cutoff, and quickly sends inhibit signal back to TX.
2. PA antanna relays release. System is now in RX state.
I realise this won't be exactly QSK-speed, but is the idea workable -
or did I just reinvent the square wheel?
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
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