[TowerTalk] Telrex Monoband matching

[NPAlex at aol.com]

Paul,
 
Additional comment on matching your TELREX mono band beams.  Regarding the 
two comments below, the Mono-bands did use a Tee matching system set for about 
50 ohms impedence.  This system was feed with a coax balun technique that uses 
a 1/2 WL cable loop from the main coax feed to the other "hot" terminal of the 
driven element.  
 
The triband series of antennas, TM-30D to TB6EM series used a stainless steel 
"hairpin" to to raise the normally low antenna source impedance to about 50 
ohms (the driven element is electrically short so that a capacitive reactance 
appears at the feed point)  The hairpin INDUCTANCE works with that capacitance 
to transform the load impedance up to 50 ohms.  This then is matched by a 1:1 
coax airwound "balun".   A multiband beam and T match are incompatible as the 
T match is frequency specific.  I am not sure what the reference to the 10m 
gadjet wire is, but there was a technique of adding a wire to the inside 
terminal of the 10m trap and "tuning" the trap to adjust the center frequency of the 
10m driven element. This is the "gimmick" approach to small values of 
capacitance.
 
 My comments to you before were incorrect, and I researched my files for a 
more accurate description.  The balun of the day was 1:1 and Hairpins, or 
T-matching was used to transform the impedance of the antenna to 50 ohms.   
 
The TELREX beam was in its day, and may yet today, the most rugged beam made. 
  No tinker toy 1-1/2" booms like some today, there's was heavy wall 3" booms 
with an external center coupler that was 3-1/2 inches in diameter.  Formed U 
straps, not U-bolts for fastening to the boom and mast.
 
Regards,
Norm W4QN
==================Previous responses ===================

yes, I have a TB6EM and it uses a T-match constructed from #8 aluminum then 
fed with a coax balun with a 10m gadet wire (old school) balun.

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Most of those old Telrex antennas used a T-Match.
Look in ARRL Handbooks and Antenna Handbooks.
Don
N8DE

============================
Quoting Paul Cassel <paul at ve3sy.com>:

> Would anyone know what the feed Impedance is for the older TELREX 10 and
> 15M532 series of antennas?  The described original ? wave 75 ohm balun 
> gives the appearance of something like a 4 or 6 to 1.
> Also looking for a manual for a 20 metre 4 element Telrex beam that is on
> about a 35 foot boom.
> Thanks all
> Paul VE3SY
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