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Author Topic: Receive issue-rig or feedline  (Read 689 times)
AF5CC
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Posts: 940




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« on: March 24, 2013, 11:53:53 AM »

I have an Icom 706 original which I have owned for the past 2 years and really like (other than the NB not being that good on consumer electrical noise).  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, and has started to show up on other bands, like 17m and 30m for the first time last night. 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. 

Someone did suggest 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.  Would an antenna problem affect some bands more than others?  I use the same antenna and feedline for all HF bands.

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
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N4CR
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Posts: 1672




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« Reply #1 on: March 24, 2013, 06:53:41 PM »

You can turn any antenna system into a long wire by loosening the shield and pulling back the coax connector from the radio until only the center pin is touching. If you do this gently and the radio comes alive, your probably revealing an antenna system problem. If you do this and not much changes, it's likely to be inside the radio. Don't key up with the coax connector half way in. Be gentle and don't jostle the radio while you are trying to isolate the problem.

Also, a rap on the radio cabinet might reveal that their is something intermittent inside the rig. Wouldn't be the first time a firm whack healed a bad relay contact momentarily.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
AF5CC
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Posts: 940




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« Reply #2 on: March 24, 2013, 07:01:20 PM »

Thanks, that is something that is easy to check.  Will have to see how it does.

John AF5CC
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KA4POL
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« Reply #3 on: March 24, 2013, 10:54:31 PM »

The RX signal goes through the band filter unit. This is switched on by relays for the respective band. So your description would suggest that there is a problem with relay contacts.
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AF5CC
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Posts: 940




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« Reply #4 on: March 25, 2013, 06:31:28 AM »

The RX signal goes through the band filter unit. This is switched on by relays for the respective band. So your description would suggest that there is a problem with relay contacts.

I have explored that possibility before. One problem is that the RX problem doesn't make sense based on the band relays. For example, 12m and 10m use the same set of relays.  The problem exists on 12m but I have never seen it on 10m.

John AF5CC
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KE3WD
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« Reply #5 on: March 25, 2013, 06:41:17 AM »

My 706 mkII seems to need to have the screws that hold down the various circuit boards hand tightened periodically to restore good grounds.  The symptoms vary, but the reported swymptom here is one of them observed.  When inside, I also disconnect and reconnect all visible board interconnects to clean the contacts with the mechanical action of doing so. 

Always the first two things I try on that rig, as it has solved quite a few weird probs that pop up from time to time. 


73
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AF5CC
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« Reply #6 on: March 25, 2013, 08:02:48 AM »

Didn't think about tightening the screws. I have had to do that on other radios that were having problems with self oscillation.  Didn't know it would hurt receive as well, but couldn't hurt to try.  Maybe try to clean the relay a little while the rig is open.

Thanks for the advice.

73 John AF5CC
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AF5CC
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« Reply #7 on: March 25, 2013, 12:16:16 PM »

It does appear to be in the radio. I tried the tapping on the case method with no luck, but when the receive level dropped on 12m, I switched over to my 6 meter beam, since it uses a different feedline.  I keyed the rig quickly.  When I switched back to the dipole the receive level was back.  Since it was keyed on a different feedline, it doesn't appear to be in the antenna system. 

73 John AF5CC
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