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inverted v

Apr 27th 2016, 00:54

0001529375H80

Joined: May 12th 2012, 23:56
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Is a balun required on a inverted v antenna,if not, why so?
Apr 27th 2016, 03:27

AA6E

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
As with other dipole-type antennas, if you're feeding them with coax, the "correct" thing to do is to use a balun to transform from the unbalanced coax cable to the balanced dipole. But many people will say that a balun is unnecessary. That's right in the sense that you will still get results that may be satisfactory for you. But without a balun, you're going to have currents flowing back to the shack on the outside of the coax shield. Those currents are actually part of the antenna radiating system and will distort your antenna's pattern in unpredictable ways. They will also cause "RF in the shack" problems, with increased RFI potential, noise pickup on receive, distortion on your audio, and (in extreme cases) making a shock hazard for the operator. Even with a balun, you can get some of these problems if the coax is not well enough isolated from the antenna -- by running it parallel and too close to the antenna, for example.

73 Martin AA6E
Apr 27th 2016, 13:16

W1VT

Joined: Apr 4th 1998, 00:00
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I have a 15M dipole that needs a balun to prevent picking up excessive noise on receive. I did comparisons with a 10M dipole/tuner running parallel a few feet away which had a balun that did not pick up an intermittent noise source. When I put on a balun with about a foot of vertical coax between the feedpoint and the balun, I could pick up just a little bit of noise. Putting the balun or choke isolator right at the feed eliminated the noise.

Zack Lau W1VT
ARRL Senior Lab Engineer
Apr 28th 2016, 15:09

0001529375H80

Joined: May 12th 2012, 23:56
Total Topics: 0
Total Posts: 0
Thank you for your reply. What type balun is needed? 1:1, 4: 1 etc.
Apr 28th 2016, 16:11

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
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http://www.karinya.net/g3txq/chokes/
This is what I use--optimized common mode chokes. A resonant inverted V typically has an impedance close to 50 ohms, so no impedance transformation is needed.

You have to be very careful when using a ferrite balun with a multiband tuner fed dipole or inverted Vee--the tuner can force power into the balun it really can't handle--the balun will heat up and the SWR will drift--it isn't unusual for the balun to burn up. Buying a kW balun and using it at 100 watts actually won't stop this from happening--the kW rating is a "best" case rating, not a "worst" case rating.

Zack W1VT

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