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Old October 31st 04, 06:06 AM
Richard Clark
 
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On Sat, 30 Oct 2004 22:10:10 -0700, "Carl J. Hixon"
wrote:
Hi Carl,

By the numbers:
(1) So how do I calculate lengths for other frequencies? ie 121.5MHz,
146.73MHZ, 123.0 MHz

By the proportion to the original frequency (this is called scalable).
This usually implies thickness too, but the variation of your
frequencies is slight enough to disregard. Besides, you need to
anticipate some trimming using the SWR meter you are asking for in
(3).

(2) Any chance of damaging my Vertex Standard VX-700 if I start playing
around with this?

Not particularly for low power and modest SWR (and probably not even
immodest SWR).

(3) Where can I finde a descent but cheap SWR meter?

Radio Shack.

73's
Richard Clark, KB7QHC
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Old October 31st 04, 05:33 PM
NN7Kex
 
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Richard Clark wrote:

On Sat, 30 Oct 2004 22:10:10 -0700, "Carl J. Hixon"
wrote:
Hi Carl-


Tho, the rest are ok- must disagree on the SWR bridge, as some of those cheap
ones (Swan Electronics was a good example, among others) used lousey sampleing
circuits in their directional couplers. What does this do?? well, as these
are NOT even close to 50 ohm , and a substancial part of a 1/4 wave, actually
introduce a mismatch! It is easy to test for- simply terminate the antenna
with a 47 ohm 2 watt resistor, and measure the swr -should be 1:1-- then reverse
the meter and measure the swr -backwards (set the pot , in the REFLECTED position
then measure the swr in the Calibrate (or forward) position again should read 1:1
I have seen some (like the swan) reading greater than 3:1 at even 6 meters! Also,
on very high swrs, have actually seen "more" power return than was in the calibrate
position (a impossible situation !) This is caused you the lousey directional couplers
in the meter, itself!
These were made for CB, not for VHF! If it doesn't pass this test- would be a good idea
to try another brand or (perferaably) borrow a Bird (or equivalent). As information--
Jim NN7K

(3) Where can I finde a descent but cheap SWR meter?


Radio Shack.

73's
Richard Clark, KB7QHC



--
To reply, remove the NOSPAM
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Old November 1st 04, 01:50 AM
Carl J. Hixon
 
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By the numbers:
(1) So how do I calculate lengths for other frequencies? ie 121.5MHz,
146.73MHZ, 123.0 MHz

By the proportion to the original frequency (this is called scalable).
This usually implies thickness too,


Thank you for the reply. Care to show me an example? I don't know which
lenghts are important, do I scale the radiator lenght, distance between
radiator and shorting stub, and / or shorting stub?

(3) Where can I finde a descent but cheap SWR meter?

Radio Shack.


I had checked at my local radio shack and the kid had no idea what I was
talking about. Walked around and said, "we must not have them." It's not a
very good store...only good at selling their toys, phones, etc. The Shack
isn't what it used to be. Can anybody recommend a brand / model for under
$100?

Thanks,
Carl


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Old November 1st 04, 03:01 AM
Lee Hopper
 
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Carl wrote:

I had checked at my local radio shack and the kid had no idea what I was
talking about. Walked around and said, "we must not have them." It's not a
very good store...only good at selling their toys, phones, etc. The Shack
isn't what it used to be. Can anybody recommend a brand / model for under
$100?

Carl -

Try HRO - Diamond makes some nice meters for under $100.00 - for instance:

Item : SX-40C
Description : 15/150W 144-470 MHZ COMPACT WMTR
YOUR HRO PRICE $79.95

Lee Hopper, NB7F
nr Portland, OR
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Old November 1st 04, 04:40 AM
Richard Clark
 
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On Sun, 31 Oct 2004 17:50:28 -0800, "Carl J. Hixon"
wrote:
I had checked at my local radio shack and the kid had no idea what I was
talking about. Walked around and said, "we must not have them." It's not a
very good store...only good at selling their toys, phones, etc. The Shack
isn't what it used to be. Can anybody recommend a brand / model for under
$100?


Hi Carl,

A quick check at their web site reveals:
http://www.radioshack.com/iphraseget...Aoid&text=&sf=
or simply put SWR Meter into their search engine.

Lee's suggestion is just as good too.

As for simple instructions, the web abounds with them for 2M, you
simply scale any one of them to your frequency. You could build one
for less than $5 and it would mostly be for the SO-239 connector that
is used as the basis for a quarter wave vertical with four radials.

Use ordinary #14 solid wi
Vertical wire, 21"
each of 4 radials, 13"
droop the radials at 45°

....or so my quick measurements show. Your mileage may vary. Consult
other authorities for a sanity check.

73's
Richard Clark, KB7QHC


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Old November 1st 04, 05:54 AM
Howard
 
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On Sun, 31 Oct 2004 17:50:28 -0800, "Carl J. Hixon"
wrote:


By the numbers:
(1) So how do I calculate lengths for other frequencies? ie 121.5MHz,
146.73MHZ, 123.0 MHz

By the proportion to the original frequency (this is called scalable).
This usually implies thickness too,


Thank you for the reply. Care to show me an example? I don't know which
lenghts are important, do I scale the radiator lenght, distance between
radiator and shorting stub, and / or shorting stub?

(3) Where can I finde a descent but cheap SWR meter?

Radio Shack.


I had checked at my local radio shack and the kid had no idea what I was
talking about. Walked around and said, "we must not have them." It's not a
very good store...only good at selling their toys, phones, etc. The Shack
isn't what it used to be. Can anybody recommend a brand / model for under
$100?

Thanks,
Carl

Carl,
I know that this isn't the answer you are seeking but I'll give it a
go anyway. Whay not just use a quarter wave? If your ultralight
aircraft has a metal framework and/or skin you could use that as the
'missing half' and just use a 1/4 wave whip. This is done in land
mobile all the time, a 1/4 wave whip that uses the vehicle body as the
ground plane. While I might be missing something by not knowing much
of anything about the aircraft you wish to mount this on it seems like
the simplest solution. I've built 3 from published measurements and
the SWR was acceptable on all (under 1.5:1) without pruning. Figure
the center frequency of where you plan to operate (on each band) cut
for that and call it a day. If you do wish to get the SWR meter
anyway another poster recommeded a Daiwa - I have one of their SWR
meters and concurr with his recommendation.
Howard
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