| Author |
Message |
    
741
| | Posted on Tuesday, June 25, 2002 - 6:49 pm: | 
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HI,
I am setting up a new base and I want to know if it is OK to use whatever size jumpers I need to connect the radio/amp/meter/TVI filter. I am going to make the jumpers myself and it would be much neater if I made the jumpers to size. If I only need 4' do I have to make a 6' jumper? If I need only 2' do I need to make a 3'. Also, what is the correct way to connect my equipment. Radio/Amp/TVI filter/Meter/Antenna or Radio/Amp/Meter/TVI filter/Antenna or Radio/Tvi filter/Amp/Meter/Antenna.
THANKS - 741 Little Red Truck |
Bigbob
| | Posted on Tuesday, June 25, 2002 - 8:52 pm: |
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That's fine if your ant.swr is 1.5 or less.Man is this gonna open a can of worms all over again. |
Biged
| | Posted on Tuesday, June 25, 2002 - 9:03 pm: |
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741,
You will probably get a few different opinions on what size jumpers to use but I will tell you from my own experience that it realy doesn't make any difference. If you were to measure your SWR's at the end of a 3 foot jumper, they might be ok, but if you were to measure it at the end of a 3' 6" jumper they just might go up. If you were to measure SWR's from the outside of the coax with out opening it up, you would see a fluctuation of readings as you moves your sensor down the cable. As far as the order in which you connect everything, it goes as follows... Radio..Amp...Meter...Filter...Antenna. You want the radio to drive the amp, the meter to read the vital's of the radio/amp, and the filter to extract unwanted TVI before it goes into the antenna. Hope this all helps...Eddie |
741
| | Posted on Tuesday, June 25, 2002 - 10:23 pm: |
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Bigbob - I do not know what my swr is because I have not set up my station yet. I am going to get a Army Stick or Imax 2000 or Maco 5/8 (MORE WORMS). When I adjust the SWR should anything be inline or just the meter and the antenna? What about the order of things? Radio/Amp/Meter/TVI/Antenna? Is that correct. I know on my old station the swr changed if I changed the order of things. I never know what is the real SWR.
THANKS |
Bigbob
| | Posted on Wednesday, June 26, 2002 - 12:10 am: |
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Make sure your main coax is in mutiples of 14' if foam dielectric,if solid polyethylene multiples of 12' then it won't matter what length you cut your jumpers,have at it. |
Dx431
| | Posted on Wednesday, June 26, 2002 - 1:52 am: |
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741, Yes, that is correct...Radio\Amp\Meter\TVI\Ant....make sure you have a good ground on your ant. also.BTW, are you using a base or a moble with a power supply? |
Marconi
| | Posted on Wednesday, June 26, 2002 - 3:21 pm: |
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IMHO the jumper length may only be important when your antenna is not at or near enough to true resonance, as when the reactance is not at or near zero, at the fequency of operation, and/or the load or some other point(s) or device(s) in the system are not showing to be truely resistive, as when the impedance is not at or near 50 ohms. This is often the condition in which we have to operate our stations.
Considering our radio systems will work efficiently over an impedance range of about 30-100 ohms and with reactance of (+-) 30 or more we often don't have problems usless we try to amplify the signal.
That said, if you are not experiencing any observable problems with your setup, then the length of your jumpers should not really matter. If you are getting by with no problems while running barefooted you may, however, begin to see some problems when adding an amp in line. Then maybe a little fine tuning of your jumpers could be a quick fix.
I agree with Bigbob, it won't matter, regarding his suggested lengths only if the load is purley resistive, well tuned, and matched. I say this partly because of something that BigEd says in his post about measuring your SWR a different points along a line. If it was my setup I would probably first try multiples of 3' as jumpers and stay with odd multiples of Bigbob's lengths (electrical 1/2 wave lines) as a lead line to the antenna.
Remember guys your 50 ohm coax is not purely 50 ohms. If it is actually a piece of 50 ohm coax, it will show us a characteristic 50 ohm impedance only if the load is purely resistive, absent any reactance. The actual impedance at any particular point along an infinently long piece of 50 ohm coax can probably vary from 30 - 100 ohms according to the ARRL Antenna Handbook.
I do not know why, but I have always been of the understanding that one should place a TVI filter directly or as close to the output of the amp as possible for it to be the most effective. I keep my audio imput down and do not run a filter, so I am not sure what works best. Actually, I have never been able to tell any difference using a filter. Something to consider, so you will just have to experiment.
Marconi |
741
| | Posted on Wednesday, June 26, 2002 - 7:43 pm: |
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Thanks for all the help. When I get my antenna, do I just use the swr meter to tune it or do I have everything inline and then adjust the swr? My station is a 2980 and a Skipper 300 Tube amp using LMR-400. I still have not made up my mind on the best antenna. I am looking at the Maco 5/8, Army Stick, Imax 2000, or a Sigma IV or even the new 1-10(I think that is the name) but $250 for an antenna is high..
741 |
Marconi
| | Posted on Wednesday, June 26, 2002 - 11:10 pm: |
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741, I believe it is always best to tune at the installed height when possible. If you can't do that then you just have to tune and raise. If you tune with everything in line, your tune could work out to be a compromise for every reactance point in the system. This can make the tuning process very difficult and problematic. It can be done but why complicate matters.
Personally, I tune right at the antenna. Occasionally I use an electrical 1/2 wave line or multiples of same to tune for the desired tuning frequency. You probably can get a better tune and it is informative to use both an analyzer and an inline SWR meter direct to the antenna with nothing else in line. After I think I have the antenna tuned well, I will compare results using the actual line I will be using with the antenna. I also check comparative results of the operational line into a dummy load before installing it to the antenna. I check the RF output, forward, and reflected, at both ends of the line using the dummy load just to see how reactive the line is going to be when the antenna is setup. I also do this with every thing in line as another check. If you keep good notes it will cut down of confusion as you setup your station.
Of the antennas you note, I would suggest going with the Maco, or the I-10K because you have better tuning control over the antenna. The I-10K is very well built and mine was very easy to tune. The Maco can be a bit more difficult to build and tune, and I am not too sure about the modern vintage as to durability. The other two antennas are basically your regular plug-&-play types. Reports I get on the Imax always seem to be very good.
I am not too sure you will be happy with the Sigma IV if it is a knock off of the modern vintage. I hear some of these imported knockoff's use very light weight aluminum. They are very long, so that could be a problem. The original three radial version and the older versions with the four radials are very good antennas.
Good luck and keep us posted.
Marconi |
CATMANKZZA1806
| | Posted on Thursday, June 27, 2002 - 10:59 pm: |
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I HAVE FOUND TO USE THE SAME LENGTH ON ALL OF MY JUMPERS. JUST SOMETHING THAT SOMEONE TOLD ME. I HAVE GREAT RESULTS OUT OF MY EQUIPTMENT...
CATMAN (KZZA1806) |
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