[Milsurplus] ART-13 Transmitter and BC-348 Receiver info

[arc5 at ix.netcom.com]

----- Original Message ----- 
From: "Mike Hanz" <aaf-radio-1 at aafradio.org>
Subject: Re: [Milsurplus] ART-13 Transmitter and BC-348 Receiver info


> I suspect the conundrum lies in the definition of "50 ohm antenna"...
> These are duck soup for an antenna engineer, but few of us are.

Indeed.   I understand reactance,  but I still have a hard time
 wrapping my mind around the resistive element of antennas. 
It's that spooky "radiation resistance."
If you tune-out the reactance, you're left with the 
loss resistance due to skin effect which, unless you're
working with microwaves, is going to be a few Ohms,
and the radiation resistance, which is a factor of the antenna's
dimensions and its effective height.  So every "ham" antenna
out there is going to be different depending on circumstance.
A quarter-wave dipole in so-called "free space" (which doesn't
exist anywhere) has a radiation resistance of around 72 Ohms.
a quarter-wave monopole (or "vertical" or "Marconi," take your pick)
over a ground plane is 36 Ohms.  
One wonders if the great radio VooDoo witchdoctors were consulting
the spirit of Maxwell when they chose "50 Ohms" as a standard.
Do you think it was because that's between a dipole 
and a monopole?

I'll tell you what I really don't understand - Feedlines!
Just what makes "50-Ohm Coax" 50-Ohms?
Someone told me to look at it as an "infinite chain of tuned circuits,"
but that don't work because it would be frequency dependant.
And if the circuits are non-reactive, then you have only loss
resistance because you have -0- effective height, and that's
going to be dependant on the length of the cable.
Ack!  I'm obviously missing "the elephant in the room" here.
So much for my feeble knowledge.

In any event- I use a non-reactive, 50-ohm resistive load
as a "standard" and get my rigs to work correctly into that
before I "release them into the wild."
It's not a perfect solution, but it's practical.
All that algebra makes my head ache ;-).

73 Dave S.