KB6NU's Ham Radio Blog

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A reader asks about VHF antennas

Posted: 19 Jul 2018 11:30 AM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email

I think Phil will have better results with a J-pole or collinear antenna.

About a week ago, I got the following email. While not strictly amateur
radio-related, it is about antennas, and I thought some of you antenna
gurus could help this guy better than I can.

Phil writes:

First, I wanna say Ive been playing with the idea of becoming an amateur
radio operator for about 50 years (dont ask) as Ive been a consumer
electronics servicer & hobbyist for as long. At present, I (and please dont
see me as a villian) operate a FM (very low power) radio station (since
2005) om 87.9 mhz and am wondering about something; Ive built antennae for
a long time & am strangely-intrigued by a poser here.

I use a homemade dipole (1/2 wave) that is center-fed (like most), but I
have taped the coax to the lower element.My results are 2 miles of
coverage. Trying a folded dipole made for 88 108mhz only goes out about
1/2 a mile. I am wondering why.

The folded dipole is the 1byone Outdoor Radio Antenna, High Gain
Omnidirectional FM Reception Antenna with Round Dipole Design. Being a
commercially-built antenna I dont understand why it gives such poor
performance. I talked to the manufacturer, but they have no answers.

Also, can you tell me why my homebrew antenna works so well when its
supposed to be a no-no to run the coax down that way? I did it for
convenience. SWR is less than 1.5 and sound quality in the car to limit is
very good.

I replied:

I don’t see you as a villain—as long as you’re not interfering with any
licensed stations and you’re filling a community need.

Now, on to your question. I’m not an antenna guru, but I think the reason
that the commercial antenna works poorly because dipoles are not meant to
operated in that configuration. They are designed to straight, not curved
like that. I rather doubt that the manufacturer did any real engineering or
ran any kind of performance tests on this antenna, nor did they compare the
results to other antennas, such as a simple dipole.

I’m also not 100% sure why your dipole configuration works with the way you
run the coax down one of the elements. Perhaps the coax has really good
shielding, thereby minimizing any kind of interaction. Perhaps it’s the low
power level.

What I’d do if I were you is to go with a J-pole or collinear antenna.
SeeÂ*https://www.kb6nu.com/can-help-reade...-base-antenna/. I think
most FM stations are vertically polarized anyway, aren’t they? (I’m not
really sure about this.) Either antenna is going to give you some gain over
a dipole and should extend your range.

If experimenting is really all you’re doing, then you really should get an
amateur radio license. Experimenting is, after all, one of the reasons that
ham radio exists, and you don’t run the risk (admittedly small) of running
afoul of the FCC. It’s not rocket science. Just get my free study guide
from kb6nu.com/study-guides.

Any of you have some other thoughts for Phil?

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