[Moon-net] IC746 transient output spikes

[LANCE COLLISTER]

Hello Dave,

Thanks for your thoughts.  Yes, I also have my station wired up just like that.  The 
question has been, however, that when the XMTR (the last thing in the sequencer line) 
is finally turned on, it produces a transient power output spike (which comes on as 
soon as the sequencer keys the PTT line), which could conceivably damage the solid 
state brick amplifier.  I understand this seems to be a problem in most ICOM rigs, 
and I have also seen the same thing with my IC706.

Here is what the ICOM technical support people instructed me to do about it this week:

> 
> 
>> Thanks for your e-mail.
>> 
>> The initial "spike" you see is simply the lag time of the APC circuit in 
>> controlling the output power. I've never heard anyone having trouble 
>> with any type of amplifier with the "spike" that you mentioned. Most 
>> amplifier builders have a lot of lattitude in the designe to allow for 
>> this "spike". Hope this will help.
>> 
>> Best Regards;
>> 
>> 
>> Mike Hilton
>> Technical Support Representative
>> 
>> ICOM America, Inc.
>> 2380 116th Ave. NE
>> Bellevue, WA 98004
>> Ph. (425) 454-7619
>> Fax (425) 637-8417
>> 

They said to basically ignore it :-(  They obviously are not talking to the TE 
Systems people, who have done testing on the IC746 in particular, and feel this IS a 
problem!  They have advised not running the IC746 rig with one of their bricks at the 
rated full power because of these transients.

Rather than simply ignore the problem, I decided to try to protect against damage to 
the solid state amp.  Since other people may have this problem, I thought I would 
share the solution that I came up with here.

Further to several suggestions related to controlling the ALC voltage, I connected a 
variable negative voltage to pin 8 of the the ACC(1) jack on the rear panel of my 
IC746 through a NC relay contact on a small relay in an outboard box I constructed. I 
set the voltage to around -4 VDC so there is no power output at all from the IC746 
when I am in XMIT mode.  The negative ALC voltage essentially suppresses any 
transmission from the IC746.

Then, using the PTT closure signal output from pin 3 of the same IC746 ACC(1)jack, I 
trigger a small time delay circuit that opens the relay, removing the negative ALC 
suppressor voltage a few tenths of a second after the IC746 has been placed into XMIT.

It may be overkill, or (according to the ICOM people) unnecessary, but at least I 
feel more confident now that I won't be destroying solid state amps with the 
transient power spikes from my ICOM transmitters!

Thanks to everyone for your help!  GL and VY 73, Lance


Dave Blaschke wrote:
> Lance
> 
> Here is my solution to all these types of problems:
> 
> TX ON sequence:
> 1. Antenna relay(s) + preamp protection
> 2. AMP  (+ brick, if used)
> 3. Transverter  (if used)
> 4. Transceiver TX out
> 
> TX OFF sequence (back to RX:
> 1. Transceiver RX in
> 2. Transverter (if used)
> 3. AMP (+brick, if used)
> 4. Antenna relay(s) + preamp protection
> 
> The ARR 1-2-3-4 sequencer works nicely for this. I have it timed to take 
> about one second to step through all four. More than enough time for 
> relay switch bounce setteling. If I am running JT65, I let the computer 
> comm port DTR/RTS trigger the sequencer.
> 
> If I am running CW, I use a manual switch to trigger the sequencer 
> (unless I am using a CW program, like CWkey5. Then I let the computer 
> comm port DTR/RTS line trigger the sequencer, just like it does with WSJT.
> The only caveat is NEVER RUN THE RADIO in break-in or VOX mode, so that 
> pressing the key cannot cause TX.
> 
> 
> Dave, W5UN
> At 20:41 3/7/2008, you wrote:
> 
>> A bit off topic, perhaps, but I know others here also have these rigs.
>>
>> I have an IC746, and have been pleased with it so far.  However, I 
>> often see RF
>> power output spikes when I switch to XMIT. This is more of a concern 
>> now, because
>> I am planning to use this with a solid state amp which cannot tolerate 
>> any such
>> excessive power input spikes.  Is there some work-around for this 
>> problem that I
>> can implement here?  I look forward to any suggestions you might be 
>> able to provide.
>>
>> Thanks and 73, Lance
>> -- 
>> Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
>> P.O. Box 73
>> Frenchtown, MT  59834  USA
>> QTH: DN27UB
>> TEL: (406) 626-5728   URL: http://www.bigskyspaces.com/w7gj
>> 2m DXCC #11, 6m DXCC #815
>>
>> _______________________________________________
>> Moon-Net posting and subscription instructions are at 
>> http://www.nlsa.com/nets/moon-net-help.html
> 
> 


-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728
URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11/6m DXCC #815