Author Topic: lost in the amings of a DIY handheld antenna  (Read 865 times)

Offline Greekman

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lost in the amings of a DIY handheld antenna
« on: August 15, 2017, 10:32:19 AM »
on a whim I "decided" to make my own HT antenna.
So i dove in the interweb and what I found was this:
http://www.arrl.org/files/file/Technology/tis/info/pdf/9803037.pdf.

I am perplexed, and cannot understand the instructions well. (let alone that the diagram is rather bad)
I know that he is building a "base-loaded short whip" by the coil he suggests.
But why is he using a short piece of coax sleeve?
I am assuming just to have some surface to coil the whip around.
Could there be another reason?

BTW, I will be making a 1/4 wave whip, so I just need to omit the coil....I think.

Offline jerseyboy

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Re: lost in the amings of a DIY handheld antenna
« Reply #1 on: August 15, 2017, 10:04:00 PM »
I never made one of these exactly. But yes, no coil if you are going to do a full quarter wave.

I think one of the things he is trying to show us is that the connector length is part of the electrical length of the antenna.

Let us know how it works out.

Jerseyboy.

Offline Greekman

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Re: lost in the amings of a DIY handheld antenna
« Reply #2 on: August 16, 2017, 12:16:09 AM »
Quote
I think one of the things he is trying to show us is that the connector length is part of the electrical length of the antenna.

that is a non-issue, I think. that is if you are going to measure SWR and cut, you will already be starting long..
I guess the final result will show, what the difference with the theoretical length will be.

BTW, while we are at it....
I am looking at RG-142 core for the whip. I assume it will be less flexible being thicker and with a teflon dielectric.
I also assume that using RG-142 as a power line still maintains adequate flex, doesn't it?

Offline Greekman

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Re: lost in the amings of a DIY handheld antenna
« Reply #3 on: August 16, 2017, 10:20:39 AM »
one more question...
What other lengths would work without a loading coil?
I will assume 3/4? 1/8? (IIRC Carl once said that odd wavelength quarters do)

Offline Carl

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Re: lost in the amings of a DIY handheld antenna
« Reply #4 on: August 16, 2017, 05:12:16 PM »
one more question...
What other lengths would work without a loading coil?
I will assume 3/4? 1/8? (IIRC Carl once said that odd wavelength quarters do)

Without special matching coils or capacitors,stick to 1/4 as the radio is half of the antenna and few radios are 15 inches or so long...you will have poor performance boost from anything over 1/4 wave and as you can't measure SWR without adding cable or analyzer to the mix...you will be better off to cut the antenna to length and LEAVE IT ALONE! Unless you plan to leave the coax and SWR meter permanently in line as they alter the antenna significantly.

Note that unless you have plenty of hardware laying around ,you can BUY this antenna at lower cost than building one from purchased parts and while it may work ,improper SWR from improper length can damage the radio Transmitter over time .
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Offline Greekman

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Re: lost in the amings of a DIY handheld antenna
« Reply #5 on: August 17, 2017, 10:53:20 AM »
Carl, i do not care to saving that little money, I just want to experiment
(let alone that my crude measurement method has shown very bad results for the cheap Chinese Ht antennas - while still showing good results for the quality ones).

what I have done is i have bought me a length of RG142 on a SMA connector. I was thinking of removing outer case and shield  initially, but I stumbled on the following design by SV1BYO.
It is a two-band whip, practically two antennas, one inside the other. So I will be experimenting with the proper length of coax shield as the UHF antenna.
(sorry for the Greek text, i cannot make the design program to produce text in English. But the principle is clearly shown on the right sketch)





Offline Carl

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Re: lost in the amings of a DIY handheld antenna
« Reply #6 on: August 17, 2017, 11:25:56 AM »
  Experiment is great reason to continue.
This is the same concept as my multiband HF as you will have two resonant lengths on one feed point.
The shortest wire should be trimmed for SWR first and then the VHF side and as they are bands with a third order multiple...expect some interaction that will effect one band while trimming for the other. As you are not using the coax as feedline,cut them to length and do not use coax velocity factor as part of your cut determination.
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If you had only one year,one month,or one day...Would you live your life differently?

Offline Greekman

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Re: lost in the amings of a DIY handheld antenna
« Reply #7 on: August 17, 2017, 11:57:08 AM »
hmmmm... problem is that the prof/designer suggests cutting for the VHF first
(but then suggests not cutting for the UHF but bridging on the lower end, changing the point as the antenna is measured. - is that the  same thing?)

thanks for the tip on the velocity factor. While i never calculate it (helps to start long) I did not know that we do NOT account for it when using coax wire.

Offline Carl

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Re: lost in the amings of a DIY handheld antenna
« Reply #8 on: August 17, 2017, 12:16:18 PM »
  Hey,go with his directions ,if you have problems ,try it the way it works best for me when making multi-wire HF antennas as they will interact...though I have done little with VHF/UHF as the Big Stick has doe all I need so far.and I can purchase antennas so cheap ($4.99 for pull up dual band 1/4 wave)

https://www.amazon.com/gp/product/B0187NXPB2/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
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Offline Greekman

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Re: lost in the amings of a DIY handheld antenna
« Reply #9 on: August 23, 2017, 06:37:11 AM »
I was thinking about the method again yesterday...
Since i will be starting long, is there a reason not to take turns cutting once for the VHF and once for the UHF?

Offline Carl

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Re: lost in the amings of a DIY handheld antenna
« Reply #10 on: August 23, 2017, 08:27:11 AM »
I was thinking about the method again yesterday...
Since i will be starting long, is there a reason not to take turns cutting once for the VHF and once for the UHF?

Sure is....because you can't cut two different length wires at the same time. ;)
Stop complaining about life and start Celebrating it .

I've reached the age where there is little left to learn the hard way.

If you had only one year,one month,or one day...Would you live your life differently?