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#1
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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 |
#2
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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 |
#3
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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 |
#4
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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 |
#5
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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 |
#6
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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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