[Moon-net] IC746 transient output spikes

[LANCE COLLISTER]

Hello Dan,

I don't use any built-in DSP functions, so I have not noticed any problems you 
described.  However, I believe controlling the output power with the ALC negative 
control voltage has solved my uncertain drive level problems.  At least, I feel a lot 
more secure now that I won't blow up an expensive solid state amp with the transient 
power spikes ;-)

Someone mentioned that the new ICOM 7000 apparently does not experience the same 
transient spikes so prevalent in their previous rigs, so I guess ICOM has finally 
figured out a solution.  My solution for my next rig is going to be an Elecraft K3 ;-)

GL and VY 73, Lance

kb5my at starband.net wrote:
> Hi all,
> 
> ICOM's response on this issue doesn't surprise me.  I traded-in my old
> IC-746 for an IC-746 PRO, thinking that the new DSP and superior noise
> reduction would be more useful for EME.  What I discovered during my first
> EME contest with the then new rig was that I was getting fatigued more
> quickly, and that the longer you listened to weak signals or no signals,
> the louder the background noise got, even though the volume and gain
> levels were untouched - and that cycling the TX or the noise reduction
> restored the low noise level temporarily, only to have it build back up to
> unacceptable levels over just a few minutes.
> 
> I did a couple of experiments where I set the radio up into a dummy load,
> unsquelched, and turned the volume down to a point that the audio could
> barely be heard when I stood across the shack 15 feet away near the shack
> door.  Then, I left it there overnight, behind a closed, solid wood door
> and heavily insulated 8-inch thick load-bearing wall.  When I approached
> the shack door the next morning, I could hear the loudly-hissing
> background noise when I was 5 feet from the solid door.  When I opened the
> door, the noise was deafening.
> 
> I wrote a carefully-worded and respectful e-mail to ICOM USA Tech Support
> about this problem, and what I got back was a tersely-worded response from
> someone who obviously couldn't be bothered to deal with a problem in an
> Amateur Radio product.  In effect, he stated that this was a known problem
> in the IC-746 PRO, and that ICOM had no plans to fix it.  That's it - not
> even an apology.  As an engineering manager who is also involved in the
> design and testing of new communications products, I found ICOM's response
> to be unacceptable.
> 
> At the time, I had been a loyal ICOM customer for over 20 years, and at
> the moment, I still possess every ICOM radio I've ever purchased, all the
> way back to the IC-211 I purchased new in 1979.  This was the first time I
> had ever been completely disappointed by ICOM.  It was enough to convince
> me that they are no longer the ICOM I had come to respect over the years,
> and that it would take an act of divinity to convince me to purchase
> another ICOM radio.
> 
> My IC-746 PRO still gets used occasionaly for VHF contests where the TX
> gets cycled a lot, but it is useless for EME.  Instead, I'm
> building up a FLEX-5000A & multiple auto-switched transverter system,
> similar to the SDR-1000 setup built by KM0T (www.km0t.com).  At least I
> know that any problems with the FLEX-5000A will eventually get addressed
> and fixed.
> 
> BTW - I used both IC-746 models to drive Lunar-Link LA-62 and LA-22 amps
> directly at the 32- and 38-watt levels respectively, and it appears that
> the LA-series adjustable ALC did a good job of clamping the 746's output
> spikes.  I never saw any excursions above 1500 watts on the LA-x2
> peak-reading wattmeters once the ALC was adjusted per Lunar-Link's
> instructions.
> 
> 
> 73,
> Dan  KB5MY
> 

-- 
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