[TowerTalk] Balun Recommendation

[Gene Fuller]

Hi Tony -

I'm a bit more casual then many on this site. Since a pennant pattern is 
nearly 120 degrees wide I use four from one center post, terminate the 
center of the vertical leg with about 850 ohms and feed at the point (at the 
center post). I use 4 short pieces of 450 ohm line down to a 
matching/selection  box, a small torroid transformer on each line provides 
approximate matching and balanced to unbalanced conversion and four small 
SPST relays select which antenna to put on the 75  ohm CATV coax back to the 
shack. I use two of these systems, either broadside or endfire with the 
switching back in the shack. If doing this it's important to keep all of the 
phasing  proper. I set it up so I could use either system by itself or the 
two together. I find I can detect some difference between using one or 
two.but considering the amount of extra effort I would say it's marginally 
worthwhile. But then, sometimes the marginal difference makes the 
difference.

Good luck with your project. Pennants are great little rx antennas. They'll 
never replace beverages but for limited realestate they're very effective.

Gene / W2LU
----- Original Message ----- 
From: "N2TK, Tony" <tony.kaz at verizon.net>
To: <towertalk at contesting.com>
Sent: Sunday, April 22, 2012 3:37 PM
Subject: Re: [TowerTalk] Balun Recommendation


>I am looking for a balun (common mode current isolator) recommendation for
> my receive loops, if I need a balun.
> Because of my lot size I only have pennant and flag type antennas. I feed
> them with a binocular core transformer per W8JI's and other's web sites
> where the primary and secondary are two separate overlapping windings. For
> my receive loops (3 fed from both directions in order to get two 
> directions
> out of each)  I bring the RG6 feedlines away at right angles for 15', then
> drop to the ground then they are underground till they get to a aluminum
> panel on my shed. The receive lines from the antennas to the shed are
> 50-130' long. They terminate at a coax switch (I feed 12V through the coax
> to switch directions on each pennant/flag) with a preamp on the aluminum
> panel. The aluminum panel is tied into my common ground with the tower,
> aluminum panel just inside the basement, AC mains box, etc. with lots of
> ground rods (27), solid #4 copper wire and Cadwelds. The RG6 feedline runs
> from the coax switch underground to the basement where it has a lightning
> arrestor and a limiter. Then it runs up to the shack.
>
> Should I add balun(s)? Where - at  the antenna feedpoints, at the feedline
> to the coax switch? Multiple places?
> For receive lines what is the recommended balun? RG6 (how many turns)
> through 2.4" (or smaller) #31 type material (how many cores?).
>
> Tnx for feedback
> N2TK, Tony
>
> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Joe Subich, W4TV
> Sent: Saturday, April 21, 2012 4:51 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Balun Recommendation
>
>
> On 4/21/2012 4:26 PM, Gary Schafer wrote:
>> Yes Ian, I agree with you that "common mode current" on a coax outer
>> shield is a complete misnomer. It doesn't describe what it is "common
>> to". If it were really common mode current it would have the same
>> current on the inner conductors as well as on the outer conductor and
>> be in phase.
>
> While common mode current may be a bit of a misnomer, it is accurate in 
> that
> the effect of "outer shield current" is identical to that of common mode
> current in a balanced system because of the "pin 1 problem"
> that K9YC has written so extensively about.  Since the signal return in 
> most
> amateur equipment is not tied to a complete and effective shielded
> enclosure, the outer shield current is *indistinguishable* from a true
> common mode current as it passes through the unbalanced input/output
> circuits of modern equipment.
>
> Again, if this "outer shield current" is sufficient it can appear in in
> microphone inputs, be fed back into audio amplifiers or even be impressed
> across control and power supply circuits.  The results can be anything 
> from
> mildly annoying to fatal to the equipment depending on the level of the
> common mode signal and the circuit involved.
>
> 73,
>
>    ... Joe, W4TV
>
>
> On 4/21/2012 4:26 PM, Gary Schafer wrote:
>> Yes Ian, I agree with you that "common mode current" on a coax outer
>> shield is a complete misnomer. It doesn't describe what it is "common 
>> to".
>> If it were really common mode current it would have the same current
>> on the inner conductors as well as on the outer conductor and be in 
>> phase.
>>
>> A better name for what is commonly called "common mode current" on the
>> coax outer shield would probably be "outer shield current".
>>
>> 73
>> Gary  K4FMX
>>
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