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Feedline Mismatch Question

Sep 2nd 2013, 13:02

W1FL

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I would like to feed a Hustler 5BTV antenna with a 50 ohm input with RG6 70 ohm cable that is available in-ground from a previous satellite installation. The cable length is approx 150 ft.

I have a Ten Tec Eagle 100 watt with built in tuner.

Is this a big incompatibility issue or will it work satisfactorily ?

Kind regards, 73's
Sep 2nd 2013, 15:26

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
The 5BTV should work satisfactorily on the 5 bands the antenna was designed.

This article by Phil AD5X describes how to attach PL-259s to the RG-6's aluminum shield with a special solder and butane torch.

http://www.ad5x.com/images/Articles/Connectorizing%20RG6.pdf

Zack Lau W1VT
ARRL Senior Lab Engineer
Sep 2nd 2013, 21:21

W1FL

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Thanks so much. Wonderful info. ARRL does it again !
Oct 20th 2013, 13:53

W1FL

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Another R6 question: The R6 works very well feeding the Hustler Vert. Since there are two R6 cables in this old sat. run. Would there be any advantage to running them in parallel from the shack to the antenna ?

Thanks,

Andy Knittle W1FL
Oct 20th 2013, 23:33

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

If you have the proper test equipment, you may be able to measure the impedances and optimize the line length of a mismatched feeder for minimum losses. Tuner losses tend to be much higher when the both the frequency and impedance are low.

It is a lot of work but can be a very educational exercise.

Zack Lau W1VT
ARRL Senior Lab Engineer
Oct 22nd 2013, 10:20

W1FL

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Thanks, however I do not use a tuner and the SWR is less than 1.5/1 on all bands. My question regarding the use of two 150 foot R6 cables in parallel has to do with the reduction of line loss. I realize the impedance would be reduced but probably the 15 ohm differential from 50 ohms will remain the same.

Thanks
Oct 22nd 2013, 13:13

AA6E

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Paralleling transmission lines won't reduce attenuation. If your line loses 10 dB (say), dividing the power between two lines that each drop 10 dB and then recombining still gives you a 10 dB loss, at best.

73 Martin AA6E
Oct 22nd 2013, 15:34

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Two 75 ohm cables in parallel will give you an impedance of 37.5 ohms if you tie the center conductors together. With a quarter wavelength multiple, you can match 25 ohms to 50 ohms with a really good SWR and no need for a tuner. Or, you can change what was a decent 100 ohm load into a really low 14 ohm load that can result really bad tuner losses. Most likely, you will get something in between these two extremes.

I've used parallel 75 ohm coax to match a 6M beam.

Zack Lau W1VT
ARRL Senior Lab Engineer


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