[ICOM] Receive level dropping-rig or antenna system issues?

bonddaleena at aol.com bonddaleena at aol.com
Mon Mar 25 12:53:58 EDT 2013 

John, did you check Icom's 'knowledge base'?
This symptom is a very common one with the 761 and no doubt the 751A. I have a MKIIg and haven't noticed any problem, but it's virtually unused. I bought it for my motorhome which I no longer have.....

ron
N4UE

 

 

 

-----Original Message-----
From: John G. <af5cc at fidmail.com>
To: ICOM Reflector <icom at mailman.qth.net>
Sent: Sun, Mar 24, 2013 7:30 pm
Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?


Hi George,

Thanks for the information. I had a similar problem recently with my 706.  I 
would key it and the radio would turn off.  Checking the fuse the a 
continuity checker made it look good, but replacing it with another fuse 
solved that problem.
Still have the receive issue, though, even with the new fuse, and it has 
always made the correct power on transmit.

73 John AF5CC
----- Original Message ----- 
From: "George Jones" <gjones04 at tampabay.rr.com>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Sunday, March 24, 2013 10:08 PM
Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?


> Recently I had a similar problem on my IC-706MKII mobile. The problem was 
> more noticeable on transmit rather on receive.  I have operated this 
> mobile for some time without experiencing any problems on a Hustler 
> antenna with separate coils for each band.  About a month ago I picked up 
> a LGG tuner at a local hamfest and installed it in the mobile. I switched 
> the antenna out to a 108-inch steel whip. The tuner worked with this 
> combination and no apparent problem for several weeks except it seemed to 
> take longer to tune on 20-meters. After many attempts to check into a net 
> on 40-meters I began to suspect a problem. My first response was to think 
> that the problem was with the tuner or new antenna combination.
> After bypassing the tuner and switching the antenna back to the Hustler 
> with 40-meter coil, the problem persisted.
>
> Out came the test equipment. First I connected a Bird watt meter and dummy 
> load to the IC-706MKII, HF/6 antenna connecter. After keying up the radio 
> in the FM mode and checking each of the HF bands, I noted that the TX 
> power would barely register any output on the Bird's lowest setting.
> Now my thoughts turned to a defective PA section on the IC-706MKII radio. 
> My previous thought that there may have been a problem with the tuner and 
> 108-inch whip combination was now confirmed and that I had damaged the PA 
> section with that antenna combination.
>
> Further test....  Out came my other IC-706MKIIG radio. After connecting 
> the second radio up the problem seem to be no better. In fact, the Bird 
> watt meter indicated the same problem.  This had me really scratching my 
> head!  I began to check the 12-volt line and noted that the voltage looked 
> good around +13.8 volts at the connector to the radio.  I even keyed the 
> IC-706MKIIG transmitter while monitoring the voltage at the connector. The 
> voltage drop noted looked to be in the normal range with only about 0.3 
> volts drop.
>
> Now with both radios on the bench in the house with an Astron 50 amp 
> supply connected, both radios produced rated power out on the Bird meter. 
> Back to the car to further check out power cable.  I connected a 12-volt, 
> 60-watt camper style light bulb to the power cable an immediately observed 
> the problem. The light bulb lit up very dimly. Using the light bulb for a 
> test instrument, I began  testing each connection along the power cable. 
> In my vehicle, an SUV, I have a #6 wire running from the battery to a 
> distribution block near where the radios are mounted. The #6 wire runs 
> through a cartridge fuse right at the battery tap. The light bulb 
> indicated a problem with the fuse. I replaced the defective fuse and now 
> both radios make rated power in the car.  Further test with the Bird meter 
> indicated that the tuner and 108-inch whip combination was working as 
> expected.
>
> What we learned from this experience is that the original fuse was 
> stressed in a manor that it would not fail until a heavy current was drawn 
> through it. A simple continuity check with an ohm meter shows the fuse to 
> be good. The voltage drop across the fuse with the bulb connected 
> indicated several volts drop. The digital volt meter alone did not provide 
> enough of a load to indicate the problem.
>
> George - W4AQR
>
> --------------------------------------------------
> From: "Larry Young" <k4lxv at bellsouth.net>
> Sent: Sunday, March 24, 2013 3:46 PM
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?
>
>> John: It should be easy to determine if it is internal or external to the 
>> rig. When the  receive is normal, attach an external signal source to the 
>> antenna input and note its level on the S meter. When the receive level 
>> drops, reconnect the same signal source and again not the S meter level. 
>> If it is the same as before when good, then obviously you have some 
>> oxidation occurring somewhere in the antenna/feedline/balun path.
>> Larry  K4LXV
>>
>>
>> --- On Sun, 3/24/13, John G. <af5cc at fidmail.com> wrote:
>>
>> From: John G. <af5cc at fidmail.com>
>> Subject: [ICOM] Receive level dropping-rig or antenna system issues?
>> To: "ICOM Reflector" <icom at mailman.qth.net>
>> Date: Sunday,
>> March 24, 2013, 3:03 PM
>>
>> Here is a message I posted a few months ago about the receive level 
>> dropping off at times in my Icom 706 original:
>>
>> "I have noticed for the past few months that the receive seems to drop
>> at times on certain bands-it started on 12m and now occurs on 15m as 
>> well. If you click the key or mic to quickly put it into transmit the 
>> receive comes back. To me this sounds like a dirty relay or one that is 
>> going bad"
>>
>> Now here are some additional details, it seems to be occurring on other 
>> bands as well. 17m at times, and was doing it on 30m last night. Someone 
>> suggested to me that it could be a problem in the antenna system as well. 
>> I did some checking this morning, and have determined that it isn't in 
>> the low pass filter, the MFJ tuner, or any jumper coaxes in the shack. It 
>> would have to be in the feedline going to the G5RV, or the balun there. I 
>> haven't had time to change out the coax run
>> yet.
>>
>> I have also noticed that on 12m and 15m the receive will come back up by 
>> itself at times. Sometimes it is a quick drop down and come back several 
>> times in succession. Would a relay problem do this?
>>
>> So, with this latest information, what is the better guess as to the 
>> problem-in the rig or the antenna system?
>>
>> 73 John AF5CC
>>
>> ----
>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>> ----
>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> To support QSL/QTH.net: http://www.qsl.net/donate.html 

----
Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
Icom Users Net: Sundays, 1700Z, 14.316 MHz
Icom FAQ: http://www.qsl.net/icom/
To support QSL/QTH.net: http://www.qsl.net/donate.html

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