[ICOM] TX Problem IC970A 2.4 GHZ module

[NICK.WALLACE]

Hi All,

I am posting this on behalf of Doug VK4OE. We were wondering if anybody else had encountered the same problem which is as follows. I will pass any info received onto him.

Thanks in anticipation.

Nick   ZL1IU

>From Doug.....


Just to save you some typing, I'll describe again what I am 
experiencing, which only relates to the 2.4 GHz module in transmit 
mode....the other features of this excellent radio are currently working 
well.

The problem is one of "fading" transmitter power as something obviously 
is heating up in the 2.4 GHz transmit path.  The scenario is that the 
radio has been switched off for a time long enough for it to cool to 
room temperature internally, then it is powered up and switched to 2.4 
GHz transmit mode (continuous, e.g. FM).  The RF output control is set 
to maximum.

It transmits the full 1 Watt for 2 to 3 minutes (or 5 minutes if ambient 
temperature is cooler) then, over a period of about a minute, the 
transmitter power gradually falls away to around 50 mW.  Whilst this is 
happening the ALC gradually climbs to a high level.

Momentarily switching to RX or switching the whole radio off briefly 
then on again do not lead to a return to 1 W output.  Only powering off 
and letting the whole radio cool for an hour or so leads to a return to 
1 W output, and being ready for the whole fault sequence to occur again.

It is conjectured that there is something wrong with one or more 
component in the RF path between the TX amplifier and the antenna 
connector, something which is thermally active.  Has anyone else had a 
similar problem and found the solution?

Thank you