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1-8 of 8 messages
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2M VHF Antenna from old TV Antenna Question...
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by KC0NVI on December 1, 2002
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Hello Everyone,
I am somewhat new to Ham Radio, and heard that I can build my own antennas, so I found an old TV antenna, and reviewed the information for building a "tiny 2", but I'm a little confused in one area.
The instructions give the different demensions for the elements being of different diameters, but the diameter of the tubing that is on this antenna I found falls inbetween those given, so I'm not exactly sure how to proceed?
I would like to build it, could anyone tell me how to proceed when the element diameter differs from that which is given?
Thank you in adavance, I really appreciate the help.
73's
Randy
KC0NVI
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RE: 2M VHF Antenna from old TV Antenna Question...
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by WA9SVD on December 1, 2002
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Hi Randy,
I'm not familiar with the "Tiny 2" so it's difficult to make specific recommendations. (If you got the design on the Internet, let us know the address and I'm sure you will get other replies as well.) The first information needed is what sort of dimensions were in the original design, and what are the dimensions of the material you intend to use? Obviously, the length you use will be "between" the lengths specified.
Give the forum a little more information, and I'm sure we'll get you pointed in the right direction.
73
Larry WA9SVD
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RE: 2M VHF Antenna from old TV Antenna Question...
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by WB2WIK on December 2, 2002
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Prompted by a previous post referencing the "Tiny 2," I did find it on line, and I can confirm:
1. Tubing diameter is absolutely not critical. You can change it by 50% one way or the other without materially impacting anything about the design or other dimensions.
2. This is not a very good design. I'd toss the TV antenna and just build a 2 element 2 meter quad using copper wire loops and wooden dowel (or anything) spreaders -- for $5, the entire antenna can be built, and will work better than a modified TV antenna.
3. Better still, last month's issue of "CQ VHF" magazine contained an article on building extremely low-cost two meter yagi antennas from scratch, using household materials and implementing an excellent, low-loss matching system. The 5 element version of that antenna would yield considerably more gain than the "Tiny 2," and not cost a penny more to build.
WB2WIK/6
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RE: 2M VHF Antenna from old TV Antenna Question...
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by KC0NVI on December 6, 2002
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Great thank you, I will have to find that issue, so I can try some of these antennas out. Being somewhat new, and not having a lot of time to do the things I'd like. But then most of us are like that I think.
Thank you for the information, I will see if I can find that issue to work with, and build some of these.
Thanks again.
73's
Randy
KC0NVI
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RE: 2M VHF Antenna from old TV Antenna Question...
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by KC0KFG on December 7, 2002
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have you given much thought to the old stand by the j-pole simple to build and they don't stick out too badly ive been using mine for years i found the plans in the arrl book but their are plans online in fact there are ones online that are simpler to tune than mine good luck to ya brian
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RE: 2M VHF Antenna from old TV Antenna Question...
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by KC0NVI on December 15, 2002
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Actually, I have made a twin lead 300 ohm J-pole. Works real well. I'm trying to figure out what I might do for a base antenna for VHF.
I've thought about the Copper Cactus idea, and that might work, the only problem that I would run into there, is the SWR's. Not having a meter to tune it with, I run the risk of messing up my only radio, and can't afford to do that.
Thanks again for all the feedback, and I will certainly keep reading through the posts here for ideas and were to find plans. Not an electronic builder, I have eye sight issues that prevent me from working with small items, as I am unable to really see them well enough to say build an SWR meter for 2mtr . But will do the best I can with what I have, and am able to work with.
Thank again All, Have a merry christmas and a happy new year everyone.
73's
kc0nvi
Randy
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RE: 2M VHF Antenna from old TV Antenna Question...
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by WB6BYU on December 16, 2002
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Randy -
If the directional/gain properties of a yagi are not
important, then I would suggest a simple ground plane
antenna. For example, take a chassis-mount SO-238
connector and solder an 18" vertical whip to the
center conductor (I like to use brazing rod for this).
For the radials, I use #12 or #14 bare copper wire.
Presuming the coax connector is the type with 4 holes,
cut two pieces of wire each 5' long, form them into
a long "U" shape, and insert the ends into two of the
mounting holes from the "inside the chassis" end of
the connector. Pull the wire up tight against the
fitting and solder. Trim each wire to 24" long from
the coax connector. (The dimensions are not the
traditional ones, but they work quite well, and the
SWR is good when the radials are angled out about 45
degrees from vertical.)
You can mount this by putting it on the end of a piece
of PVC pipe, with the coax running up the center.
A PVC end cap over the top (with holes for the radiator
and radials sealed with silicone caulk) will provide
weather proofing.
On the other hand, if having some gain and directivity
is important, I'd suggest you check out some of the
quad and yagi designs at www.cebik.com
In the article "New Quad Studies" he gives formulas
for determining quad dimensions based on the frequency
and wire diameter. I built the 3-element quad from
these formulas (which I put into a handy spreadsheet)
and fed it directly with coax and the match was very
good WITH NO ADJUSTMENTS. Similarly his wide-band
yagi designs are quite good - look for the "OWA"
designs, many of which are designed for direct 50 ohm
feed. There is a good 3-element design hidden in the
article on choosing a 3-element beam (I think it is in
the "Upper HF - Yagis" section. This is a wide-band
3-element yagi designed for a direct 50 ohm feed.
Although the original design is for 10m, the antenna
can be scaled up to 2m, where it is only about 26"
long. The combination of wide bandwidth and 50 ohm
feedpoint impedance should mean that by cutting the
elements to specified length and using an insulated
boom, the SWR should be low enough that you can use
it without any tuning.
Meanwhile, watch for a cheap CB SWR meter at the next
hamfest - I often find them for $5. They may not be
perfectly accurate, but usually quite adequate to
determine "low" or "high" SWR (and, most useful when
making adjustments, to indicate "lower".)
Good luck, and let me know if you need help converting
the yagi dimensions to whatever material you have
available for building them.
- Dale WB6BYU
wb6byu@arrl.net
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RE: 2M VHF Antenna from old TV Antenna Question...
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by K5QE on March 24, 2004
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No one has mentioned it, but it is very important to understand that FM activity is vertically polarized while SSB/CW activity is horizontally polarized. The J pole and ground plane are fine for local repeater activity, but hopelessly inadequate for DX work on SSB/CW. The "cheap yagi" designed by Kent Britain, WA5VJB, is a great entry level antenna for either the FM(turn it vertical) or for SSB/CW(use it horizontal) modes. Here is a link to one article on the web describing these interesting and very inexpensive antennas. URL= http://www.clarc.org/Articles/uhf.htm
I built a 6el 440FM version of this antenna for 83cents!! I used 3 ft of approximately 1 1/4" OD PVC pipe and #10 bare copper wire. The 83 cents was the cost of the PVC pipe at the hardware store. I just drilled through the PVC and force fit the elements through the holes. The antenna works great and the SWR is flat across a large part of the 440FM band.
A stacked pair of the longer "cheap yagis" gives about the same gain as a very expensive commercial yagi. Stacking a pair horizontally gives a very good antenna for DX work and you absolutely cannot beat the cost.
Welcome to the wonderful world of VHF DX. Good luck es 73's Marshall K5QE
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