Ian,
its due to the inter-relationship between CW and AM.??? The 20W
you mention will be CW only.??? On SSB you will get 20W PEP.??? On
AM you will also get 20W PEP.
But AM is not normally measured as PEP.?? Its measured in steady
carrier power.??? And to get 20W PEP of AM, the carrier power has
to be 1/4 of the peak power.? Hence 5W of AM.
Its a point skated over by many people when rating power
outputs!???
Amateur radio limits demonstrated the same logic.??? It used to
150W of DC input power to your PA.??? That would generate about
100W of carrier power, but 400W PEP.??? Hence when SSB arrived the
power limit became 400W PEP.....
best regards
Richard
G7RVI
You wrote
? TRA-931
From: gm0uhc
Date: Sun, 23 Mar 2025 09:29:23 PDT
Hi,
I currently have on my bench a Racal Syncal 30 aka TRA931. I'm
currently involved in looking into alternative PA transistors
since good 2N5070s are nearly impossible to source these days.
I currently have a pair of 'experimental' transistors in place
and the set is happily generating 20W on all frequencies with a
very slight drop (about 2W below 2MHz). What is a bit alarming is
that the set will happily deliver 20W (in the High position) even
when AM is selected. Oddly, although the manual specifically
states that the o/p is nominally 5W on AM (and understandably
too), there is no mention in the circuit description of how this
reduction in output power is achieved.
?
Looking at the wiring associated with the Mode Switch, it looks
like the Mute pin (66) on the synthesiser might have something to
do with it, but poking around in that area has proven
inconclusive.
?
Can anyone shed some light on this?
?
Regards,
?
Ian, GM0UHC
