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MIXED COAX

Aug 12th 2011, 18:13

N8CHR

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I am going to put up a 40 meter dipole which I will cut for 7.100.
I"m also planning on running this on 20 meters at 14.225 and up. Will I get a good pattern? Ant will be about 40 feet high pretty much in the open


#2 and most important, Can I mix RG8X coax and RG58?
I have a considerable length of both but not enough of just one.

Thanks Tom
N8CHR
Aug 13th 2011, 05:35

KE8DO

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
You did not say how much power you will be running or if you have a tunner and of what type. On 20 meters, the input to the 40 meter dipole is going to be a very high Z, and some tunners may not be able to match it. I have not looked at the pattern, but I would add a second wire for a 20 meter dipole connected to the same coax at the same point as the center of the 40 meter dipole. That would help your pattern and also solve the problem of very high SWR on 20 meters. There will be a little interaction between the two antennas but they should work OK.
I see no problem mixing RG8X and RG58, they are both 52 ohm. I would not want to run too much power to RG58 with a high SWR, as you would have using a 40 meter antenna on 20 meters. You will have points of high voltage and high current that the RG58 may not be able to take.
73 Don KE8DO
Aug 15th 2011, 14:39

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
With 100 ft of LMR-400, or low loss RG-8 sized coax, you can expect 8.5 dB of loss on 20M--the tuner will add another dB of loss. This much loss is pretty significant on 20M voice and video.

You might consider "A Folded Skeleton Sleeve Dipole for 40 and 20 Meters" by Joel W1ZR in the May 2011 QST, pp 58-61. It uses window line to ease construction.

Zack Lau W1VT
ARRL Senior Lab Engineer

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