Fw: Re: Fw: Re: Fw: [Antennas] Tuner Inductor Q

Sun, 5 Jan 2003 20:56:55 -0600

A bead balun is good, Danny. 

I was also looking at alternative baluns. On the one hand 
AG6K talks about toroid balun loss and then uses a 30ft 
piece of RG58U on 10m. That's why I decided to use two 
lengths. The main disadvantage of that is still the size and 
packaging. I know there are many arguments for using toroids, 
but I haven't found any which are good (low loss) from 
160m to 10m. The local club does a lot of 160m QRP and 
KW work, believe it or not. An alternative might be to 
switch between two toroids ....one for 160-40m, another 
for 40-10m. Sure would make a nicer looking tuner and 
easier to keep symmetrical.

Sometimes I think the reason the MFJ type tuners create a 
radiation problem is that unbalanced and unshielded lines
radiate ....like inside the tuner. How many other "antennas"
do you have attached to your MFJ ? Couple that with 
whatever (generally not great) grounding scheme you have 
in your shack and there it is.

Balanced lines don't radiate. If you can keep the whole 
thing as symmetrical as possible, it won't radiate even 
with plastic covers. If you can do the symmetrical thing, it 
behoves you to get from unbalanced to balanced as quickly 
as possible from the coax input.

73  Kees K5BCQ  

--------- Forwarded message ----------
From: Dan Richardson <[email protected]>
To: [email protected]
Date: Sun, 05 Jan 2003 17:58:34 -0800
Subject: Re: Fw: Re: Fw: [Antennas] Tuner Inductor Q
Message-ID: <[email protected]>

At 05:54 PM 1/5/2003 -0600, you wrote:
>Any on a completely different tuner subject, the "Balanced, Balanced
>Antenna Tuner" by AG6K is gaining in popularity at the local club, I
>may build one. Looks like a great tuner but I would add a switchable
>choke balun on the frontend ....30-33ft of coax for 160m through 40m
>and around 12 ft of coax for 20m through 10m. Using the 30-33ft length
>at 10-20m is too much loss and not required.

Hi Kees,

I built one of those tuners and it seems to work okay, but on closer 
analysis you'll find that it still has a problem with common mode 
(voltage/current) stress on the balun. In fact, under some conditions it 
*may* add to the problem rather than reduce it. While that design does 
address the differential impedance the balun sees it doesn't do the same 
for the common mode impedance. If your antenna is well balanced and the 
feed line it routed so as to reduce induced common mode current I think 
you'll be happy with it.

BTW: I used a W2DU bead balun (90 beads - almost double the recommended
50) 
as it is a lot less bulky than a big roll of coax.

73
Danny
K6MHE

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