Nick C wrote:
Roy,
Thanks for the update. I just read those postings. That V antennas looks
similiar to what I have, except I feed at the end of my wire. Also, my wire
isn't terminated and is not grounded. (Whenever I ground my wire, I get a
severe loss of signal...?)
Anyway, after seeing the price of their antenna, I quickly decided that mine
isn't so bad after all...
A couple of quick questions:
1. It sounds like, at least for my suburb environment, I'm probably not
going to improve my reception by having a yagi antenna. So, as you said,
it's better to reduce the noise coming into the receiver. I get a lot of
QRM from non-atmospheric noise... although it seems like recently, the
atmospheric noise has been really bad. (Even WWV doesn't come in without
extra noise.)
It's hard to say. If the noise is primarily from one direction, AND it's
not the direction of signals you want to listen to, AND the Yagi has
reasonable rejection of signals coming from the noise source (which
might be at an elevation angle where Yagi rejection isn't very good),
then a Yagi would help. Otherwise, you're right, it wouldn't. I agree
that the odds are against it helping much.
2. I've never measured the SWR of my antenna. Will this have any affect on
my signal reception? I was under the impression that SWR was really only
valid if you're transmitting energy..?
No, the SWR won't affect your reception. If the noise level drops when
you disconnect your antenna, then improving the SWR won't help a bit.
3. Really dumb question here. If a branch from a tree is touching my wire,
then is my antenna effectively cut in length... from that point to my
feedpoint? My construction of the antenna was done rather quickly, so if
this is the case, then I'll need to relocate the wire.
A dry tree touching the wire probably won't have any effect. If the tree
is wet, its effect on the antenna depends on the frequency and where it
touches the antenna. If it touches at a high-impedance point (near an
integral number of half wavelengths from an end), it'll effectively
connect the tree to the antenna. If it's at a low impedance point (near
an odd number of quarter wavelengths from an end), it won't have an
appreciable effect.
(FYI, currently, I have rougly a 100ft length of wire, which actually is in
a V-shape... almost the shape of the house. The wire itself is a good 30ft
off the ground... which should be 'above' the QRM levels of the surrounding
houses. My endpoint is a simple balun which converts the wire Z to 50ohms
... and then I use low-loss coax to my rig.)
I'm just looking to 'improve' my design if that's possible... and definitely
increase my S/N ratio as you suggested.
It sounds like you're end feeding the antenna. If so, even with the
balun, your feedline is almost certainly a major part of the antenna.
You might make a substantial improvement by center feeding your antenna,
with a balun at the feedpoint. The balun won't be effective at all
frequencies, but even where it isn't, your feedline will be much less
part of the antenna than when it's end fed. It's quite possible that the
feedline is picking up the local noise more strongly than it's getting
distant signals, because it's closer to potential noise sources and
because it's probably more vertical than the antenna itself. So reducing
feedline pickup could improve your signal-to-noise ratio. I recommend
giving center feeding a try.
Ironically, you might have found that the Yagi makes quite an
improvement -- but not because of its gain. People replacing something
like you've got with a properly fed Yagi that's high and in the clear
often find a big improvement, and mistakenly attribute it to the Yagi's
gain. What they don't realize is that if they'd put a dipole up in the
same place with the same care, they'd see just about the same improvement.
Thanks for your time.
-Nick
Hope this is helpful. If it is, it's time well spent.
Roy Lewallen, W7EL
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