[Amps] ACOM 2000A and Two Transmitter In-Band Operation

[wc1m73 at gmail.com]

Strange. When there's a problem with T/R sequencing, the amp normally
reports a relay sequencing problem or that it's seeing RF at the wrong time.
An arc fault indicates a problem at the 2000A's output.

It could be that you have an intermittent issue with the antenna, the
feedline, connectors, etc. that's causing a momentary change in impedance
(or an open or short circuit), and the 2000A is more sensitive to it than
the Alpha 99.

You could eliminate the possibility that there's a T/R sequencing error by
feeding the 2000A's KEY OUT signal to the mult radio (use diodes if you need
to combine it with another source of TX INH.)

73, Dick WC1M

-----Original Message-----
From: g4piq at btinternet.com <g4piq at btinternet.com> 
Sent: Thursday, November 18, 2021 6:11 PM
To: amps at contesting.com
Subject: [Amps] ACOM 2000A and Two Transmitter In-Band Operation

Like many multi-op contest stations, at M6T we have the ability to operate
two interlocked stations on the same band, and for the mult station to
interrupt the transmission of the run station to call a needed QSO / mult on
the same band, grabbing the same amplifier and antenna. 

 

This is the sequence

1.	Run radio is transmitting
2.	Mult radio sends PTT line low, 
3.	the run radio is immediately inhibited from transmitting (TX-INH
line on K3)
4.	a relay switches the amplifier input to the Tx output of the second
radio
5.	after a software configured delay (and I've tried delays of several
hundred ms as a test) - the second radio starts generating RF 
6.	the second radio drops its PTT line
7.	TX-INH on the run radio stays asserted for another few hundred
milliseconds
8.	Run radio starts transmitting again.

 

All this time, the PTT line to the amplifier is held low.

 

My problem is that, when doing this, quite frequently the ACOM2000A
amplifier will trip off with an arc fault - and at differing stages in the
process. Drive level is not excessive, and reducing the drive power on with
radio appears to have no significant effect. Both radios are K3s which are
normally well controlled from a power transient persective. 

 

I just wondered if anyone had a solid method for keeping an ACOM2000A
on-line in this scenario - other than swapping it for a less fussy
amplifier! A reasonably well protected Alpha 99 doesn't fault in this
scenario. 

 

73,

 

Andy, G4PIQ