The Survival Podcast Forum

Survivalism & Self Sufficiency Topics => The HAM Radio Board => Topic started by: Greekman on April 08, 2019, 02:58:19 PM

Title: Coax matching cable?????
Post by: Greekman on April 08, 2019, 02:58:19 PM
Hi all!  I just saw that he uses a length of 75 ohm cable as a match for his loop antenna.
https://youtu.be/N26zAmCInJQ

What's the theory for this?  And how dors one calculates impedance and length?
Title: Re: Coax matching cable?????
Post by: Smurf Hunter on April 08, 2019, 04:06:41 PM
You can match anything, given the right transformer.  With a 50ohm transceiver and 50ohm antenna connected with 75ohm feedline, a current balun (transformer) isn't even needed in a theoretically lossless and perfectly match antenna.  That would only have an SWR of 1.5:1.  Any radio would happily tolerate such a close match.

I used 75ohm frequently for receiving antennas, because the coax is often free from cable TV companies.
The bigger problem is not the impedance matching (math), rather the loss.

You can google for coax loss calculators, which should drive your coax selection more than the impedance.

Title: Re: Coax matching cable?????
Post by: armymars on April 08, 2019, 04:52:40 PM
Smith Chart.