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Author Topic: coax length from transciever to tuner or amp  (Read 864 times)
N7UVH
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Posts: 12




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« on: January 06, 2007, 08:08:12 AM »

Hello,

I have a ts450sat to a MFJ tuner to a SB220amp.
my question is  the coax jumpers to each unit, is there a magic coax length to keep the radio seeing 50ohms.  The 450 radio, once it sees 1.5 swr rolls the power back.  I know I have 1.5 or less swr when I have antenna tuned with tuner or using a antenna that is 1.5 or less.  So I am thinking the jumper coax from the 450 to tuner is a odd length, which is 2.5 feet of rg8 with no bad connections.  Thought if I tryed a diffrant lenght the 450 would see closer to 50 ohms. What is do not is use the 450's auto tuner to take out the 1.5 to 2.0 swr out to the tuner.

Now with the amp is a diffrant matter.. for I know I have to get in and retune the amps inputs, infact I think I have some bad caps.

Any one mess with coax jumper lenghts and wonder if it would be the same as using the .66 factor

Tnx
Pat
n7uvh
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K7KBN
Member

Posts: 2765




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« Reply #1 on: January 06, 2007, 01:41:09 PM »

Pat - this isn't CB, it's ham radio.  There is no "magic length" for coax except that it has to be long enough to reach from point A to point B with a few inches of slack.

Think about it: if the length WERE critical, every time you changed bands you'd have to disconnect everything you had for the band you were on and install the corresponding cables for the band you're moving to.  By which time the band you're moving to will probably be dead.

Adjust the antenna correctly; not the coax length.
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73
Pat K7KBN
CWO4 USNR Ret.
AA4PB
Member

Posts: 12685




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« Reply #2 on: January 06, 2007, 02:59:33 PM »

Once the amp input is properly tuned you shouldn't need a tuner between the radio and the amp.

The length of the coax jumpers won't matter. Even if you had a high SWR (which you shouldn't) on the jumpers, they are so short in terms of wavelength on HF that there length won't change the impedance at the other end significantly.
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K7UNZ
Member

Posts: 691




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« Reply #3 on: January 06, 2007, 05:39:54 PM »

Your connections should be:  Radio -> Amp -> Tuner -> Antenna -> world......

Do not use your radio's tuner to tune the input to the amp, unless you have both the amp off and the external tuner in bypass mode.  You are then tunning the antenna system.  A correctly aligned/adjusted amp will not need an external tuner on it's input.

Coax length is a non-player, it just has to be long enough to reach the next piece of equipment in the shack.  

73, Jim/k7unz



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