[ICOM] ICOM 736 on 60 meters

D C *Mac* Macdonald k2gkk at hotmail.com
Thu Mar 15 20:27:52 EDT 2012


Nothing had changed, antenna-wise, Larry. One 
day it worked and next day it did not. 
 
A couple of repair places have said it might 
be one of the tuner motors. I would guess 
that something has happened to the logic 
and an incorrect selection is made at the 
point where frequency hits 3.9. 
 
It's beyond my ability to decipher and I sure 
as heck don't want to get in there and REALLY 
screw things up!
 
I guess I need to pack it up and send it to 
Scott Malcolm at MTS. 
  
* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* k2gkk at hotmail.com * 
* (Since 30 Nov 53) * 
* Oklahoma City, OK * 
* USAF, Ret (61-81) * 
* * * * * * * * * * * 
 
 
 
> Date: Thu, 15 Mar 2012 15:47:51 -0600
> From: xxw0qe at comcast.net
> To: icom at mailman.qth.net
> Subject: Re: [ICOM] ICOM 736 on 60 meters
> 
> Have you changed anything on 80m such as antenna, antenna length, 
> feedline length etc. that might explain why it currently does not tune 
> above 3.9MHz? Otherwise I don't know what it might be without taking 
> the antenna tuner apart.
> 
> Good luck.
> 
> 73,
> Larry, W0QE
> 
> On 3/15/2012 2:50 PM, D C *Mac* Macdonald wrote:
> > Actually, Larry, the problem with 746 tuner is ONLY at
> > or above 3.900 MHz. Radio works fine on all 80 meter
> > frequencies (without tuner) and tuner works on any
> > 80 meter frequency below 3.900,000 MHz.
> >
> > If tuner mode is engaged, you can hear received signals
> > drop (greatly) when you tune up from the bottom and the
> > display hits the 3.9 point. Again, all is okay when tuner
> > is not selected.
> >
> > * * * * * * * * * * *
> > * 73 - Mac, K2GKK/5 *
> > * * * * * * * * * * *
> >
> >
> >
> >> Date: Thu, 15 Mar 2012 11:35:26 -0600
> >> From: xxw0qe at comcast.net
> >> To: icom at mailman.qth.net
> >> Subject: Re: [ICOM] ICOM 736 on 60 meters
> >>
> >> Mac,
> >>
> >> I doubt it. The basic issue is straightforward. If the 80m low pass
> >> filter (which obviously passes all signals through 4.0 or probably
> >> 4.3MHz) has significant loss at 5MHz (60m) then the low pass filter
> >> causes the power transistors to see bad SWR, low power output, and high
> >> DC power consumption. This will not be fixed by the tuner which is
> >> between the low pass filter and the antenna. Does this make sense?
> >>
> >> The tuner issue may be something completely different. Generally the
> >> Icom tuners are a type of high pass Tee network with the inductance
> >> being fixed depending on the radio frequency. It is possible that the
> >> tuner with the inductor value set for 40m may have damaged some
> >> capacitor in the tuner which is why you now see the problem below 3.9MHz.
> >>
> >> I have used a 746Pro on 60m often including the internal tuner without
> >> any ill effects so far. Obviously the original 746 is somewhat
> >> different but both radios use the 40m low pass filter on 60m.
> >>
> >> 73,
> >> Larry, W0QE
> >>
> >> On 3/15/2012 10:38 AM, D C *Mac* Macdonald wrote:
> >>> Hi, Larry.
> >>>
> >>> My IC-746 (original) had its tuner function fail
> >>> above 3.90000 MHz. Works fine below that freq.
> >>> Radio works fine 3.9 plus either to dummy load
> >>> or LDG tuner.
> >>>
> >>> I wonder if use on 5 MHz may have caused the
> >>> tuner failure. Any ideas? We may have to retract
> >>> my comments at the end of your page.
> >>>
> >>> * * * * * * * * * * *
> >>> * 73 - Mac, K2GKK/5 *
> >>> * Oklahoma City, OK *
> >>> * * * * * * * * * * *

 		 	   		  


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