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

gmacari gmacari at tampabay.rr.com
Mon Mar 25 16:49:33 EDT 2013 

Try it on a dummy load.
That will tell you if the antenna is at fault or not.
 Original Message ----- 
From: "John" <af5cc at fidmail.com>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Monday, March 25, 2013 3:25 PM
Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?


> Found the Icom knowledge base but didn't really find anything for
> those rigs or for the 706 that seemed to be related to my issues.
>
> 73 John AF5CC
>
> On Mon, Mar 25, 2013 at 12:05 PM, John <af5cc at fidmail.com> wrote:
>> Hi ron,
>>
>> Do you remember what the problem was with the 761 and 751A?
>>
>> 73 John AF5CC
>>
>> On Mon, Mar 25, 2013 at 11:53 AM,  <bonddaleena at aol.com> wrote:
>>> 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
>>>
>>>
>>> ----
>>> 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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