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Multi conductor cable for VFO 122




 
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Author Topic: Multi conductor cable for VFO 122  (Read 344 times)
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WD4DMZ
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« on: March 14, 2017, 12:50:42 PM »

Hello all. The cable connecting the VFO to my Viking 2 is a bit short and the insulation is getting old.

It is multi-conductor for the B+, filament and rf signal and is fully shielded.

Where can I get something to replace it?

Thanks, Rich
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wa2roc
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« Reply #1 on: March 15, 2017, 06:59:27 AM »

The power cord on my 122 VFO connected to my Viking II consists of only low voltage (300 volts if I remember correctly) filament voltage, a key line and ground.  Check the manual, and if you don't have one, it's available from several sources online free.

The RF signal cable bring the VFO output to the VII is a piece of coaxial cable about 24" long (again, check the 122 manual for exact length) that terminates in a PL-259 coax connector.
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Dick Pettit WA2ROC 
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WD5JKO
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« Reply #2 on: March 15, 2017, 07:12:30 AM »


If the intention is to lengthen the coax cable, realize that EFJ used low impedance coax in a high impedance circuit.
As a result the cable capacitance per foot length is part of the design. Perhaps you can use a longer piece of coax that has a lower capacitance per foot (RG-62?) such that the cable capacitance with the longer length is the same as it is now?

Jim
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WD4DMZ
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« Reply #3 on: March 15, 2017, 10:55:23 AM »

Thanks for the info. I have replaced the rf line with a new piece of RG59 cut to the specified length and that works fine.

The power connection via the octal plug is a brown cable with the B+, filament and the keyer wire as noted. My concern is that the leads are all in a single shield. Is it necessary to shield those lines? I have 300 volt multi-conductor cable but it is not shielded.

Johnson went to great lengths with the V2 to minimize RFI but perhaps that is not really a need. If not I will use some Heathkit power supply wire that I have.

Any concern with using unshielded wire?

Rich
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MikeKE0ZUinkcmo
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« Reply #4 on: March 15, 2017, 10:57:51 AM »

A couple comments.   The Viking 122 VFO has only 2 tuning ranges, 1.75 - 2.0 MC, and 7.0 - 7.45 MC. All other band frequencies are generated in the multiplier stages of the associated transmitter.

The original coax cable was 3 feet of RG-59.   The coax was connected to the plate through a 150pF cap.   The actual power cable had 4 wires, Ground, with the Filament, B+, and key lines each separately shielded according to the schematic.  

I refurbished my 122 some time back and fabricated what I suspect to be at least the second "new" 3' power cable for it.   I used stranded hook-up wire for the power cable wires and a piece of RG174 for the RF out.   I've had no operating problems with the un-shielded power cable.

Mike
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WD4DMZ
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« Reply #5 on: March 15, 2017, 11:33:35 AM »

Thanks for the info Mike. Your good experience without the shield for the power lines is what I needed.

Rich
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Pete, WA2CWA
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« Reply #6 on: March 15, 2017, 04:43:32 PM »

I would suggest reading  Section 4 b, page 9, and Operation, 1 c, 1 d,  page 20 of the VFO 122 manual. The cable is actually part of the broadly tuned output circuit of the VFO 122. Changing the parameters, length of cable, type of cable, etc. could affect performance of the VFO.
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MikeKE0ZUinkcmo
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« Reply #7 on: March 16, 2017, 11:18:36 AM »

True it will make some difference, but the actual capacity differential the plate sees with the 150p in series with the OP cable, is on the order of 13 PF, 56pF W/RG-174 vs 43pF W/RG-59.   Don't think that's all that important in this case, at least my VII, and TBS-50 don't seem to care.  

I would suspect the OP will most likely use 59 anyway since most folks don't have any 174 laying around.   I use it for everything around here almost, since I've got better than a half mile of the stuff.
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