[Boatanchors] Re: GB> An Old Idea - and a caution!

[Carl]

----- Original Message ----- 
From: "J Forster" <jfor at quik.com>
To: "Glen Zook" <gzook at yahoo.com>
Cc: <boatanchors at mailman.qth.net>; <hbr at mailman.qth.net>; 
<N2EY at aol.com>; <drakelist at zerobeat.net>
Sent: Saturday, August 02, 2008 11:01 AM
Subject: Re: [Boatanchors] Re: GB> An Old Idea - and a caution!


>
>
> Glen Zook wrote:
>
>> Back in the "goode olde dayes" many baluns did not make it much down 
>> below 50 MHz.  However, those manufactured in the past two or three 
>> decades should be fine for HF use.  This is because certain functions 
>> on cable television utilize frequencies below 5 MHz and the baluns 
>> had to pass this frequency. [snip]
>
> ========
>
> Why? In cable systems, the cable coax goes directly into the cable box 
> where anything that uses non-TV frequencies would be located. A balun 
> would be on the output of the cable box, at the TV. The TV has no use 
> for anything below Ch 2.
>
> FWIW,
> -John
>


Agreed. When I was involved with CATV based data systems we ran slow 
speed 9600 modems down to 5 mHz. Everything was 75 Ohms and the TV 
signals were all in the standard cable band. Wideband 10-20 MB data was 
above that.

Ive swept many TV baluns, new and old and its a crap shoot what will 
work as a 4:1 balun even on HF, much less MF. In most cases the balun 
becomes just a piece of wire the lower you go. Its a whole lot easier to 
wind your own on a small ferrite core and have it do what its supposed 
to; you can then even wind for several ratios that are switch 
selectable.  Since the balun is bidirectional the same switchable 
circuit can be used with a low power TX to better match open wire line 
at a particular frequency.

Carl
KM1H


> ========
>
>>  Even though I wrote an article that was in Electric Radio a while 
>> back about using TV baluns (it can be found on my website) I did 
>> "check" with a friend who was in the cable television field for 
>> decades.  From him I learned about the frequencies below 5 MHz and 
>> the fact that the baluns had to "pass" these frequencies.
>>
>> I obtained a number of baluns from him to use on my equipment.  They 
>> cost like $3 or $4 from places like Radio Shack and like 10 cents 
>> each in the quantities that the cable television people used to 
>> purchase.
>>
>> The baluns that came from the cable television industry definitely 
>> make it down to 160 meters and do a pretty good job all the way to 
>> the bottom of the AM broadcast band.
>>
>> Glen, K9STH
>
> _______________________________________________
>