RadioBanter - View Single Post - RG-6 for HF?

RHF · January 4th 08, 08:00 AM posted to rec.radio.shortwave

On Jan 3, 9:21*pm, Telamon
wrote:
In article ,
*D Peter Maus wrote:

Telamon wrote:
In article ,
*D Peter Maus wrote:

Telamon wrote:
In article ,
*D Peter Maus wrote:

RHF wrote:
On Dec 30, 9:37 pm, D Peter Maus wrote:
Brian wrote:
I finally got a house out in the woods on five acres and I'm
going to set up a couple of pretty long wires and my Wellbrook
ALA-1530. I've pretty much decided on RG-6 for a couple of 150
ft. runs because the stuff's dirt cheap and I can pick it up at
the local Home Depot. Is the impedance mismatch here going to
be negligible, or should I just bite the bullet and go with
RG-8 or a similar 50 ohm coax?

-Brian
- *Alone, your receiver won't care. I doubt that the Wellbrook would,
- either.
-
As a complex, however, you're going to have not one mismatch, -
but - two. One at the output of the Wellbrook loop, and one at -
the input - of - the antenna interface. This may result in
standing waves on the - transmission line which, in turn may
result in irregularities in - performance.
-
- With a reasonably well designed receiver, you'll likely not -
notice - any losses in practical listening. And unless you are
working at the - very limits of performance on signals very far
down in the noise and - doing A/B tests of one coax over another,
you'll not detect the - performance irregularities.
-

DPM,

Then it becomes a Practical Implementation and CBA type Problem.
CBA = Cost Benefit Analysis
http://en.wikipedia.org/wiki/Cost-benefit_analysis
http://en.wikipedia.org/wiki/Implementation

Cost of RG58/RG8 Coax Cable -versus- Cost of RG6 Quad-Shield
Coax Cable with a 75-to-50 Ohm Matching Transformer at each
end.

Starting with the Concept of a 9:1 Matching Transformer for General
Broad-Band Shortwave Radio (High Frequency 3~30 MHz) Use and
Application with 30 Turns (9-Side) and 10 Turns (1-Side) and the Same
Ferrite Core Material :

We now need a Matching Transformer to take the Antenna and Radios
SO-239 Jack/Plugs {BNC Connector Optional} -to- the 75 Ohm Coax
Cable with an F-Connector {BNC Connector Optional} .

The 50 Ohm 10 Turns (1-Side) should be understood.

Getting to the 75 Ohm (X-Side) should be simple Math :
75 / 50 = 1.5
Square Root of 1.5 = 1.225
Therefore the 75 Ohm (X-Side) would have 12 Turns.

A 75 Ohm to 50 Ohm [1.5:1] Matching Transformer would have
12 Turns (1.5-Side) and 10 Turns (1-Side) and the Same Ferrite
Core Material -as- 9:1 Matching Transformer for General Broad
Band Shortwave Radio (High Frequency 3~30 MHz) Use and
Application.

Anyone Else Have Any Ideas : On a Building Your Own {DIY}
a 75 Ohm to 50 Ohm [1.5:1] Matching Transformer ?

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - -

The Next Question Becomes : At What Cost ?

* Are the 75 Ohm to 50 Ohm [1.5:1] Matching Transformers
commercial available ? - a Ready Made Item ? Price ?

* Are the 75 Ohm to 50 Ohm [1.5:1] Matching Transformers a
Low Cost "Built-it-Yourself" Item ? - DIY Price ?

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- - - - - - -

DPM - I go back to your first statement : "Alone, your receiver
won't care. I doubt that the Wellbrook would, either."

IMHO - For the vast majority of Shortwave Radio Listeners (SWLs)
Practical Implementation Says : Just Do It ! - Use the RG6 Coax
Cable -and- enjoy listening to your radios - iane ~ RHF
*.

* *Which was precisely my point.
It's dumb to buy cable or anything else that is not matched to the task
unless there is some kind of over riding factor such as cost.

* *In your universe, and mine, yeah, you buy the best, brightest,
matched, optimized, or NFL approved.

* *Truth is, that in real world operations within the normal parameters
hobbyists achieve, there is likely no detectable difference between the
'correct' choice, *and the most economical choice for transmission line
in this application. And given that the OP was concerned about cost, his
choice is a decent one.

* *And unless the OP is intending to operate his system at the limits of
performance, any losses incurred will not be relevant to his operation.