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Author Topic: Troubleshooting Collins 30L-1. Clean unit but way high swr reading  (Read 9419 times)
KD7KTV
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Posts: 8




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« on: July 16, 2013, 09:34:50 AM »

I bought my Collins 30L-1 amplifier used at a swap meet last fall from A reputable
Estate dealer.

Dealer told me that it worked.
I eventually Broke down and bought the Ameritron interface box
To be able to key the Collins from my Icom 706.

The 706 works great thru a modern auto tuner into a g5rv.

When I hook up the Collins and key it from the Icom the Icom reports
Full on high swr.

I forgot to bring my dummy load and power meter to the beach shack
Here in Oregon.

Any ideas on troubleshooting this swr problem?

Thx much,

jim
Kd7ktv

Btw hro staff calls me an appliance user, but I'm a happy appliance user Smiley


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AA4PB
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Posts: 13032




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« Reply #1 on: July 16, 2013, 09:40:46 AM »

The amp input is not supplying a 50 Ohm load to the transceiver. Perhaps the tuned input circuits on the amp need alignment. Have you tried all bands?
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G3RZP
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Posts: 4965




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« Reply #2 on: July 16, 2013, 09:53:02 AM »

At one time, Collins specified a certain length of coax to go between the exciter and the 30L1. Later on, this did change - but a suggestion has been made that the original specified length enhanced the rather marginal stability on 15 and 10.

As AA4PB says, try the input tuned circuit alignment. If it was driven by a tube transmitter with a pi network, it wouldn't necessarily have been a problem.

Does the 706 show high SWR at all power levels when driving the amp? Is the problem on all bands?
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W1QJ
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Posts: 1521




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« Reply #3 on: July 16, 2013, 10:43:57 AM »

What type of tuner are you using after the amp and before the G5RV?
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WX7G
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Posts: 6332




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« Reply #4 on: July 16, 2013, 11:14:41 AM »

What is the input VSWR?
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KD7KTV
Member

Posts: 8




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« Reply #5 on: July 16, 2013, 11:16:11 AM »

Thank you so much for the responses.
The SWR appears high on all bands except 28 MHz.

There is no tuner involved in this set up.

I have about a 2 foot length of coax going from the 706 to the Collins amplifier. There is about a 20 foot run of coax out to the G5 RV antenna.

Where would I find a tutorial on the input circuit alignment?
Would I need an oscilloscope or a local oscillator?

Thank you.
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KD7KTV
Member

Posts: 8




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« Reply #6 on: July 16, 2013, 11:17:10 AM »

On all bands except 28 MHz SWR reads infinite on the ICOM 706.
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K5RT
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Posts: 169




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« Reply #7 on: July 16, 2013, 11:40:03 AM »

Lets start with the obvious first?

Do you hear any signals on the IC-706?

If you do, leave the amp in the line, turned off and check the SWR again.

Are you hearing the T/R relay in the amplifier switch when you key the transceiver?

Are you sure the cable between the IC-706 and the amplifier is good?

Paul


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KD7KTV
Member

Posts: 8




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« Reply #8 on: July 16, 2013, 12:53:09 PM »

Yes, the obvious.
Yes I do hear signals on 706.
I left the amp in line, turned off and checked the SWR. The low bands 7 MHz 40 MHz 21 MHz all read high SWR only the 28 MHz showed low SWR; probably just the inherit of the g5rv.

I decided to put my auto tuner back in line before the Collins. 
It will do its number on the 20 meter band and get a match.
But when I key up to talk the tuner goes back into auto tune mode.

I've tried two different cables between the Icom and the radio.
Both are newer and work fine without the Collins in my normal config: Icom to
Tuner to g5rv.

Any ideas?
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AA4PB
Member

Posts: 13032




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« Reply #9 on: July 16, 2013, 01:32:24 PM »

I left the amp in line, turned off and checked the SWR. The low bands 7 MHz 40 MHz 21 MHz all read high SWR only the 28 MHz showed low SWR; probably just the inherit of the g5rv.

Any ideas?

When the amp is off then the antenna relay in the amp bypasses the amp circuit and connects the input directly to the output. The result is that the G5RV is connected directly to the radio and the SWR on the G5RV is what you should see at the radio.

When you have the amp turned on and key the radio then the output of the radio is connected to the input of the amp. The SWR seen by the radio is, at that time, whatever mismatch occurs between the jumper coax and the input circuit of the amp. At that time the output of the amp is connected to the antenna and the amp sees the SWR of the G5RV.

Collins recommends a jumper cable length of 20.5 feet between the radio and the amp input. I assume the length works with the input circuit to provide a reasonable impedance match for the radio.

The other problem is that with no tuner between the amp output and the G5RV the tune and load controls on the amp may not have enough range to match the impedance of the G5RV on all bands.

What I would do is put a 50 Ohm dummy load on the output of the amp in order to eliminate the variable of the G5RV SWR during testing. Use a 20.5 foot length of RG58 between the radio and the amp input. Then see if you can get a reasonable SWR at the radio when you key the amp. and if you can load the amp for full output into the dummy load. If so, then connect the amp to the G5RV and see if you can load it properly for full output on at least some bands. You may need to get a high power tuner in order to provide the amp with a reasonable SWR on some bands.
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K7KBN
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Posts: 2840




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« Reply #10 on: July 16, 2013, 01:50:26 PM »

I'd certainly suggest getting a copy of the manual, which covers much of what you're asking.

http://bama.edebris.com/manuals/collins/30l1/
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73
Pat K7KBN
CWO4 USNR Ret.
KE3WD
Member

Posts: 5689




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« Reply #11 on: July 16, 2013, 02:22:45 PM »

On all bands except 28 MHz SWR reads infinite on the ICOM 706.

Suspect that coax jumper between the two first. 

Check continuity from end to end of coax and shield, also check for short. 

Substitute another known good coax jumper. 


73
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WX7G
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Posts: 6332




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« Reply #12 on: July 16, 2013, 03:07:59 PM »

Is there something wrong with the IC-706 VSWR reading? If it was high as reported the amp would not "work great." That is, the radio would not drive the amp with enough RF power.
« Last Edit: July 16, 2013, 03:13:01 PM by WX7G » Logged
WB2WIK
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Posts: 20666




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« Reply #13 on: July 16, 2013, 03:15:08 PM »

What is the model of the auto tuner??
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KD7KTV
Member

Posts: 8




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« Reply #14 on: July 16, 2013, 03:26:36 PM »

Would a 50' run of coax work or does it have to be 20.5 feet?


The 100 watt capable tuner I have is an ldg electronics at-100 pro auto tuner .
I only tried this between the Icom 706 and the Collins.

The dealer told me I  didnt need a tuner
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