[ICOM] Amp Keying Question Again

[Adam Farson]

Hi Dave, 

My understanding is that there is a short delay between switching from
receive to transmit and the appearance of RF energy at the output socket.
This delay is easily measured with a dual-trace oscilloscope.

I have never heard of damage to the T/R relays in any of the Icom amplifiers
due to early application of drive. I have been using a Yaesu Quadra
amplifier with various Icom exciters for 6 years, without any sign of relay
damage. One can assume that there is a delay as mentioned above - but a
measurement would confirm the assumption. When time allows, I shall attempt
to measure the time delay between assertion of ACC(2) Pin 3 and the first
appearance of RF output.

The reflectometer in the exciter's PA output will reduce hot-switching
stress by folding back the drive during the open switching interval. It is
still better, though, to delay the onset of RF output by a few mS after the
exciter asserts the ACC (2) SEND line.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of David J. Ring, Jr.
Sent: 21 June 2005 23:59
To: ICOM Reflector
Subject: Re: [ICOM] Amp Keying Question Again

How about sequencing, Adam?  When keying from ACC(2) pin 3 of the ICOM
exciter, does that pin switch at xx milliseconds before r.f. is generated?

In otherwords, can I hook up my amplifier relay to ACC(2) pin 3 have the
relay be energized and then the ICOM exciter generates r.f.?

I've seen some elegant solutions to hot switching - including a bucket
brigade delay which divided the voice signal (which activated the VOX) into
two components - the first activated the amplifier relay.  The second was
time delayed by 20 ms by the bucket brigade digital delay and then fed to
the microphone input of the exciter.

Thus no hot switching - and no missed first sylables caused by VOX clipping
because the VOX was turned on by the "real-time" speech, but that speech was
delayed digitally and fed to the exciter - so it never got chopped off.  No
need to say "ahhhhh".

The problem with some of the digital modes, and CW QSK is that the r.f. is
hot switched.  I've seen amplifiers that show this damage - it often causes
the relays to arc over and burn up - especially with high power commercial
installations.

I haven't investigated this with the ICOM radios, I wonder if anyone has.

73

David N1EA


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