[Moon-net] IC746 transient output spikes

[LANCE COLLISTER]

Per Sjölander wrote:
> Hi Lance,
> 
> Reading your concern about the spikes is very interesting.
> 
> And the response from ICOM is scaring.
> 
> 
> 
> We had a thread going for the same issue a year or two back on a local
> reflector and I made a very simple test with my 706.
> 
> I found this spikes in the start of every single cw dot or dash ant tried to
> put in the negative ALC voltage as you have done.
> 
> But I used a potentiometer to adjust the negative voltage for setting the
> maximum output power from the rig and used no relay to take it away.
> 
> With that setup all spikes was gone and the cw-output also a lot cleaner in
> spectra. But be careful when you reach the output level set by the internal
> power control because then the spikes will slowly return.
> 
> 
> 
> So to my knowledge there is not just a key/PTT-up spike problem but an every
> single cw dot and dash ALC-problem.
> 
> You have to be nice to your SS-amps :-)
> 
> 
> 
> gl73
> 
> /Per SM3JQU
> 
> 

Hello Per,

MNI TNX for your reply.  Your observations are very useful, and also agree with 
observations recently made at TE Systems.  I received another email from TE 
Systems yesterday, clarifying that they had also measured IC746 power output 
spikes not only at the beginning of the XMIT cycle, but all through the XMIT 
cycle!  They now send out a warning sheet with all their amplifiers warning about 
using their solid state amplifiers with ICOM rigs :(

Based on this new information and your good results, I am modifying my ALC control 
circuit here to apply the maximum negative ALC voltage all the time to the rear of 
the rig, and then only reduce the ALC voltage to some adjustable pre-set level 
slightly after the rig is placed into XMIT.  That way the power level will always 
be set by the ALC voltage, as you have done.

Since I just received another big 12 VDC power supply, I now have extra DC power 
to waste, so I may also run the IC746 at full power and attenuate the output to 
get the proper drive for the solid state amps.  This approach was suggested by 
many as the approach they use to deal with the problem. I recently purchased some 
non-inductive high power resistors to make a 100w attenuator pad.

Neither is a very elegant solution, but until I get a K3, I think I am stuck with 
the ICOM and needing to make a work-around or run the risk of destroying the solid 
state amplifiers.

TNX again and VY 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