4:1 coaxial baluns
 

Yes I know I can look this up....

Am currently feeding a 20M single triangular quad loop about 3 metres
off the ground with a 1/4 wavelength 75r Q section. Modelling the loop
shows a high-ish Z of 180 ohms. Not a problem for this feed method
though. (I expected it to be around 120 ohms)

Thinking of making it work on 10M and Z I think is around 350 ohms, but
I havent modelled it.

If I use a 4:1 coaxial balun cut for 20M, does the 4:1 effect (now a
full wavelength) also occur on 10M?

(Thinking a 3/4 wavelength Q section is the same as a 1/4 wavelength one
when it comes to translating the Z)

I am not and will not be using a tuner... (in case anyone wants to
suggest it)

TIA Bob VK2YQA

Bob Bob wrote:

If I use a 4:1 coaxial balun cut for 20M, does the 4:1 effect (now a
full wavelength) also occur on 10M?

It works on the odd harmonics, not the even--I published a computer
model of a 2M/70cm balun in the January 2000 QEX RF column. However,
as the coax multiple goes up, the phase change also goes up, compared
to a shorter balun, making long baluns impractical.

73--Zack W1VT

Reprints of the article are available for a nominal charge from the
ARRL.

(Thinking a 3/4 wavelength Q section is the same as a 1/4 wavelength
one
when it comes to translating the Z)

I am not and will not be using a tuner... (in case anyone wants to
suggest it)

TIA Bob VK2YQA

"Zack" wrote in message
ups.com...
Bob Bob wrote:

If I use a 4:1 coaxial balun cut for 20M, does the 4:1 effect (now a
full wavelength) also occur on 10M?

It works on the odd harmonics, not the even--I published a computer
model of a 2M/70cm balun in the January 2000 QEX RF column. However,
as the coax multiple goes up, the phase change also goes up, compared
to a shorter balun, making long baluns impractical.

73--Zack W1VT

Reprints of the article are available for a nominal charge from the
ARRL.

(Thinking a 3/4 wavelength Q section is the same as a 1/4 wavelength
one
when it comes to translating the Z)

I am not and will not be using a tuner... (in case anyone wants to
suggest it)

TIA Bob VK2YQA

If it is a closed loop, it works on even harmonics. A balun that is rated
3 - 30 MHz should work fine on 10 m. Theoretically, you need a 2:1 or 2.25:1
balun. Note that the latter is (3/2)^2. The 1/4 wave matching section won't
work, because it will be 1/2 WL on 10m.

Tam/WB2TT

"Bob Bob" wrote in message
...
Yes I know I can look this up....

Am currently feeding a 20M single triangular quad loop about 3 metres
off the ground with a 1/4 wavelength 75r Q section. Modelling the loop
shows a high-ish Z of 180 ohms. Not a problem for this feed method
though. (I expected it to be around 120 ohms)

Thinking of making it work on 10M and Z I think is around 350 ohms, but
I havent modelled it.

If I use a 4:1 coaxial balun cut for 20M, does the 4:1 effect (now a
full wavelength) also occur on 10M?

(Thinking a 3/4 wavelength Q section is the same as a 1/4 wavelength one
when it comes to translating the Z)

I am not and will not be using a tuner... (in case anyone wants to
suggest it)

TIA Bob VK2YQA

Instead of a coax balun, its easy enough to wind your own using a toroid,
and a 'transformer-type like that has a wider bandwidth.
those 1/2-wave u-bent baluns are good for one band usually. what you're
doing is catching the phases where the difference in voltage is twice normal
voltage. (Doubled the voltage) square that, and your impedence is
quadrupled.
If you triple the voltage, the impedence increases by 9. If you wind a
transformer you can make it close to any impedence you want....
lets say you have a length of coax is a 1/2-wave on 14.2 mhz
it would be a full wave on 28.4 mhz
it would be 3/4 wave at 21.3 mhz




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I am not and will not be using a tuner... (in case anyone wants to
suggest it)

So did you tell someone that you would never be caught dead using a turner
once?
c'mon, they ain't all that bad, mate.


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Gidday Hal

Its a function of difficult placement (rented house) and limited stay...
And I havent got one and dont want to make/buy as I am about to move to
another country. grin Also the HF privs are pretty new to me and when
I move I'll lose them!

One day...

Tnxs for your previous comments BTW. So a fullwave length of coax as 4:1
balun 0n 10M will have a minimal effect on the end of feedline Z. I'd
need an antenna that exhibited 50r on 10M and 200r on 20M.

I have been often suspicious of toroidal baluns (loss etc). I might make
one and plug it into the network analyzer at work to test.

Cheers Bob

Subsititute bcnuup for bcnntp if you wish to email direct.




Hal Rosser wrote:
I am not and will not be using a tuner... (in case anyone wants to
suggest it)


So did you tell someone that you would never be caught dead using a turner
once?
c'mon, they ain't all that bad, mate.


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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.818 / Virus Database: 556 - Release Date: 12/17/2004

" I have been often suspicious of toroidal baluns (loss etc). I might make
one and plug it into the network analyzer at work to test.

Cheers Bob

For loss: Make 2- connect them back to back for the network analyzer, then
divide the observed loss by 2.

Dale W4OP

Bob Bob wrote:

I have been often suspicious of toroidal baluns (loss etc). I might make
one and plug it into the network analyzer at work to test.

Try it in the real world. That's the best test. I use a 4:1 (feeding a low lop)
for a different reason. It makes my TS870 auto tuner 'happy' and allows
autotuning from 40 thru 10. Coax feed works fine, as does direct (no balun) open
wire feed using an external tuner, but that requires retuning on each band, and
I like to band hop. But my bandswitching laziness is not the point. The point is
that I've tried numerous balun in-out tests on the air and have yet to find
anyone on the other end that could tell a difference. I know there is loss
because the balun does get warm on some bands, but apparently it is not
detectable on the other end - which is what counts in the final analysis. So
don't take these guru's "don't do this/that with a bulun" too seriously. Try it.
If it works, well....it works... ;)

"AaronJ" wrote in message
...
Bob Bob wrote:

I have been often suspicious of toroidal baluns (loss etc). I might make
one and plug it into the network analyzer at work to test.

Try it in the real world. That's the best test. I use a 4:1 (feeding a low
lop)
for a different reason. It makes my TS870 auto tuner 'happy' and allows
autotuning from 40 thru 10. Coax feed works fine, as does direct (no
balun) open
wire feed using an external tuner, but that requires retuning on each
band, and
I like to band hop. But my bandswitching laziness is not the point. The
point is
that I've tried numerous balun in-out tests on the air and have yet to
find
anyone on the other end that could tell a difference. I know there is loss
because the balun does get warm on some bands, but apparently it is not
detectable on the other end - which is what counts in the final analysis.
So
don't take these guru's "don't do this/that with a bulun" too seriously.
Try it.
If it works, well....it works... ;)

There you go - if you let everyone else give you the answers, you'll be
missing one of the fun things of the hobby - experimenting. I played around
with winding baluns a few years ago so I could use 300-ohm line to feed an
antenna 200 feet away. It worked. I put one balun on each end of the run.


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Zack wrote:
Bob Bob wrote:

If I use a 4:1 coaxial balun cut for 20M, does the 4:1 effect (now
a
full wavelength) also occur on 10M?

It works on the odd harmonics, not the even--I published a computer

"It" refers to the balun, not the antenna. The balun works on odd, but
not even harmonics. Anyone have a simple explanation for explaining
whether something will work on harmonics or not? For instance, how do
you explain that a 40M bugcatcher won't exhibit a 15m resonance?

Zack Lau W1VT

model of a 2M/70cm balun in the January 2000 QEX RF column. However,
as the coax multiple goes up, the phase change also goes up, compared
to a shorter balun, making long baluns impractical.

73--Zack W1VT

Reprints of the article are available for a nominal charge from the
ARRL.

(Thinking a 3/4 wavelength Q section is the same as a 1/4
wavelength
one
when it comes to translating the Z)

I am not and will not be using a tuner... (in case anyone wants to
suggest it)

TIA Bob VK2YQA