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

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

On 20 Dec 2004 12:22:28 -0800, "Zack" wrote:

For instance, how do
you explain that a 40M bugcatcher won't exhibit a 15m resonance?

Hi Zack,

If so, it merely offers that across frequency, the same Parts do not
add to the same Whole.

73's
Richard Clark, KB7QHC

Zack wrote:
For instance, how do
you explain that a 40M bugcatcher won't exhibit a 15m resonance?

Because one runs into self-resonance long before 3x the frequency?
--
73, Cecil http://www.qsl.net/w5dxp


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An antenna or transmission line has resonances at (or near) odd
harmonics. But a lumped LC circuit doesn't. A bugcatcher is a
combination of the two. I'd think it likely that it has multiple
resonances, but not at harmonically related frequencies.

If you want a rule of thumb, don't look for harmonically related
resonances in any antenna containing a significant amount of lumped L or
C, or L and C distributed over a relatively small distance.

Roy Lewallen, W7EL

Zack wrote:

"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

"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.


---
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