[AMRadio] 50 ohms simple question


RBethman rbethman at comcast.net
Thu Apr 5 15:30:48 EDT 2007


Geoff, Alan, Et al,

Both of you are RIGHT - BUT - almost EVERY radio/amplifier will tune 
from 50 ohms to about 75 ohms.

So futzing with the antenna MAY not be NEEDED!

An inexpensive way to check is to borrow an MFJ antenna analyzer, I.e., 
MFJ-204B currently going for $89.95.

OR simply put a GOOD VSWR bridge between the Final and the antenna.  See 
what it tells you!  My bird with peak reading tells me that my HT-32, 
Heath TX1, DX-60, and TS-930SAT, TS-820S -> and FINALLY the T-599 will 
ALL tune to the simple standard dipole.

 From OLD BAs to newer <groan> Sand State, I have found that ALL will 
tune in this range OR more.

Bob - N0DGN

Geoff/W5OMR wrote:
> Alan Beck wrote:
>> Basic question
>>
>> Why is it that my radios are 50 ohms and the impedance at the feed 
>> point at
>> the antenna (pure dipole) is 70 ohms.
>>
>> Am I mistooken
>
> No, yer not mistaken.... but, if you want to lower the input impedance 
> to your dipole, bring the legs down to around 40 degrees, and you'll 
> drop the input impedance to the antenna down around 20 ohms.
>
> -- 
> 73




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