In article , John S
wrote:

EZNEC says the feed-point impedance at the bottom "V" is:

80M 1639 - J 11890 ohms
40M 128.9 + J 0.4186 ohms (design center)
30M 3364 - J 409.1 ohms
20M 222.6 + J 171.4 ohms
15M 119.5 + J 301.5 ohms
10M 401.1 + J 412.7 ohms

Not including the effects of tree proximity, of course.

Thanks for doing this. Many Windows programs will run under CrossOver (a
Mac implementation of WINE) on my Mac, but unfortunately EZNEC is not
one of them.

When you say bottom "V" do you mean you are you feeding the thing down
where the two sloping legs come together near ground level? That wasn't
my plan; I would have an insulator up in the air halfway between the two
high tree branches, and attach a balun and the coax feed line at that
point. The low point at the back, where the two sloping legs meet, would
simply have them joined together there (or not, on 80 and 30) and I
wouldn't feed it there.

What frequencies in each of these bands did you use? I'm a bit surprised
at the relatively high reactance on 20, 15 and 10. I'd want to cut the
thing for the CW ends of the bands. Unless you cut the antenna right at
the bottom end of the band, the harmonic resonances march up into the
bands as you move to the higher frequency bands, so I'd expect the
antenna to be too short at the CW ends of the bands on the higher bands.
E.g. if design frequency is 7.05 MHz then we're looking at 14.1 MHz,
21.15 MHz, and 28.2 MHz whereas I'm going to want to operate around
14.05, 21.05, and 28.05.

Also the high resistance and high capacitive reacance for your figures
on 80 and 20 makes me suspect that your analysis is with the loop closed
on those bands. My idea was to walk around to the back and unclip the
jumper there, so that instead of a loop, on 80 and on 30 it would be a
doublet all bent into a sloping triangle, somwhat more than a half wave
long on 80 and a bit les than 3/2 waves long on 30. I'm taking into
account end effect only at the "ends", where the two sloping wires are
now detached from each other, on 30. So the 5% shortening would only
apply to the last quarter wave on each side (ending at that low-height
insulator), not to the two half wave sections either side of the center
insulator, and since 492*2 + 468 = 1452, I'd expect the resonant length
at 10.125 MHz to be 1452/10.125 = 143.4 ft, while 1005/7.05 = 142.55 ft
would be the calculated length for a full-wave 40 m loop. So I'd expect
relatively low resistance at the feedpoint on 80 and 40, with reactance
moderately high and inductive on 80 (where it's a good bit too long for
a half-wave) and pretty low and slightly capacitive on 30 (where it's
just a bit too short for 3/2 wave).

If you ran the analysis with the loop closed on those two bands, would
you mind doing it over with the loop open?


In article ,
wrote:

I suppose it would work. Another option which I've used
camping a number of times is a dipole with insulators
breaking up the various bands. You can then use short
jumper wires with clips to bypass the insulators for low
band use.
I usually used a 80 meter dipole as the full length,
and then insulators/jumpers for whichever higher bands
I'd want to use.
One advantage to this system is no tuner needed, and no
tuner losses. And it can be fed with light coax, and the
current balun, which should keep the feed line fairly
cool at the operating position.

Would be kind of like this for 80/40/20.

o----o----o--00--o----o----o

That was my first idea. But you have to lower the antenna to change
bands. With my loop/non-loop all you have to do when you switch between
40/20/15/10 on the one hand and 80/30 on the other, is to walk around to
the back of the antenna and clip or unclip the jumper which is only a
few feet off the ground. At age 77 I'm pretty lazy and lowering/raising
the antenna to change bands is not my idea of how to enjoy a backpacking
trip at the end of a long day. Put the thing up once before supper and
take it down once after breakfast sounds like less effort. Before I
bought a Bear Vault to use instead of ropes in trees for food
protection, I had to haul the food up after supper and lower it before
breakfast. Doing something similar several times with an antenna just to
change bands? No, thanks.

David, VE7EZM and I hope soon W7???

--
David Ryeburn

To send e-mail, change "netz" to "net"

On 5/23/2013 7:59 PM, David Ryeburn wrote:
In article , John S
wrote:

EZNEC says the feed-point impedance at the bottom "V" is:

80M 1639 - J 11890 ohms
40M 128.9 + J 0.4186 ohms (design center)
30M 3364 - J 409.1 ohms
20M 222.6 + J 171.4 ohms
15M 119.5 + J 301.5 ohms
10M 401.1 + J 412.7 ohms

Not including the effects of tree proximity, of course.

Thanks for doing this. Many Windows programs will run under CrossOver (a
Mac implementation of WINE) on my Mac, but unfortunately EZNEC is not
one of them.

When you say bottom "V" do you mean you are you feeding the thing down
where the two sloping legs come together near ground level? That wasn't
my plan; I would have an insulator up in the air halfway between the two
high tree branches, and attach a balun and the coax feed line at that
point. The low point at the back, where the two sloping legs meet, would
simply have them joined together there (or not, on 80 and 30) and I
wouldn't feed it there.

What frequencies in each of these bands did you use? I'm a bit surprised
at the relatively high reactance on 20, 15 and 10. I'd want to cut the
thing for the CW ends of the bands. Unless you cut the antenna right at
the bottom end of the band, the harmonic resonances march up into the
bands as you move to the higher frequency bands, so I'd expect the
antenna to be too short at the CW ends of the bands on the higher bands.
E.g. if design frequency is 7.05 MHz then we're looking at 14.1 MHz,
21.15 MHz, and 28.2 MHz whereas I'm going to want to operate around
14.05, 21.05, and 28.05.

Also the high resistance and high capacitive reacance for your figures
on 80 and 20 makes me suspect that your analysis is with the loop closed
on those bands. My idea was to walk around to the back and unclip the
jumper there, so that instead of a loop, on 80 and on 30 it would be a
doublet all bent into a sloping triangle, somwhat more than a half wave
long on 80 and a bit les than 3/2 waves long on 30. I'm taking into
account end effect only at the "ends", where the two sloping wires are
now detached from each other, on 30. So the 5% shortening would only
apply to the last quarter wave on each side (ending at that low-height
insulator), not to the two half wave sections either side of the center
insulator, and since 492*2 + 468 = 1452, I'd expect the resonant length
at 10.125 MHz to be 1452/10.125 = 143.4 ft, while 1005/7.05 = 142.55 ft
would be the calculated length for a full-wave 40 m loop. So I'd expect
relatively low resistance at the feedpoint on 80 and 40, with reactance
moderately high and inductive on 80 (where it's a good bit too long for
a half-wave) and pretty low and slightly capacitive on 30 (where it's
just a bit too short for 3/2 wave).

If you ran the analysis with the loop closed on those two bands, would
you mind doing it over with the loop open?

7.05MHz 117.3 - J 0.2996 ohms closed loop
3.525MHz 9.365 + J 111.4 ohms open loop
10.125MHz 253.9 + J 60.16 ohms open loop

On 5/24/2013 7:16 AM, John S wrote:
On 5/23/2013 7:59 PM, David Ryeburn wrote:
In article , John S
wrote:

EZNEC says the feed-point impedance at the bottom "V" is:

80M 1639 - J 11890 ohms
40M 128.9 + J 0.4186 ohms (design center)
30M 3364 - J 409.1 ohms
20M 222.6 + J 171.4 ohms
15M 119.5 + J 301.5 ohms
10M 401.1 + J 412.7 ohms

Not including the effects of tree proximity, of course.

Thanks for doing this. Many Windows programs will run under CrossOver (a
Mac implementation of WINE) on my Mac, but unfortunately EZNEC is not
one of them.

When you say bottom "V" do you mean you are you feeding the thing down
where the two sloping legs come together near ground level? That wasn't
my plan; I would have an insulator up in the air halfway between the two
high tree branches, and attach a balun and the coax feed line at that
point. The low point at the back, where the two sloping legs meet, would
simply have them joined together there (or not, on 80 and 30) and I
wouldn't feed it there.

What frequencies in each of these bands did you use? I'm a bit surprised
at the relatively high reactance on 20, 15 and 10. I'd want to cut the
thing for the CW ends of the bands. Unless you cut the antenna right at
the bottom end of the band, the harmonic resonances march up into the
bands as you move to the higher frequency bands, so I'd expect the
antenna to be too short at the CW ends of the bands on the higher bands.
E.g. if design frequency is 7.05 MHz then we're looking at 14.1 MHz,
21.15 MHz, and 28.2 MHz whereas I'm going to want to operate around
14.05, 21.05, and 28.05.

Also the high resistance and high capacitive reacance for your figures
on 80 and 20 makes me suspect that your analysis is with the loop closed
on those bands. My idea was to walk around to the back and unclip the
jumper there, so that instead of a loop, on 80 and on 30 it would be a
doublet all bent into a sloping triangle, somwhat more than a half wave
long on 80 and a bit les than 3/2 waves long on 30. I'm taking into
account end effect only at the "ends", where the two sloping wires are
now detached from each other, on 30. So the 5% shortening would only
apply to the last quarter wave on each side (ending at that low-height
insulator), not to the two half wave sections either side of the center
insulator, and since 492*2 + 468 = 1452, I'd expect the resonant length
at 10.125 MHz to be 1452/10.125 = 143.4 ft, while 1005/7.05 = 142.55 ft
would be the calculated length for a full-wave 40 m loop. So I'd expect
relatively low resistance at the feedpoint on 80 and 40, with reactance
moderately high and inductive on 80 (where it's a good bit too long for
a half-wave) and pretty low and slightly capacitive on 30 (where it's
just a bit too short for 3/2 wave).

If you ran the analysis with the loop closed on those two bands, would
you mind doing it over with the loop open?

7.05MHz 117.3 - J 0.2996 ohms closed loop
3.525MHz 9.365 + J 111.4 ohms open loop
10.125MHz 253.9 + J 60.16 ohms open loop


Those are free-space values. I forgot to put the ground in. Here they
are revised for the bottom to be about 1.3m above ground...

7.05MHz 123.6 - J 0.02019 ohms closed loop
3.525MHz 13.57 + J 105.7 ohms open loop
10.125MHz 261.7 + J 14.89 ohms open loop

On 5/24/2013 7:56 AM, John S wrote:
On 5/24/2013 7:16 AM, John S wrote:
On 5/23/2013 7:59 PM, David Ryeburn wrote:
In article , John S
wrote:

EZNEC says the feed-point impedance at the bottom "V" is:

80M 1639 - J 11890 ohms
40M 128.9 + J 0.4186 ohms (design center)
30M 3364 - J 409.1 ohms
20M 222.6 + J 171.4 ohms
15M 119.5 + J 301.5 ohms
10M 401.1 + J 412.7 ohms

Not including the effects of tree proximity, of course.

Thanks for doing this. Many Windows programs will run under CrossOver (a
Mac implementation of WINE) on my Mac, but unfortunately EZNEC is not
one of them.

When you say bottom "V" do you mean you are you feeding the thing down
where the two sloping legs come together near ground level? That wasn't
my plan; I would have an insulator up in the air halfway between the two
high tree branches, and attach a balun and the coax feed line at that
point. The low point at the back, where the two sloping legs meet, would
simply have them joined together there (or not, on 80 and 30) and I
wouldn't feed it there.

What frequencies in each of these bands did you use? I'm a bit surprised
at the relatively high reactance on 20, 15 and 10. I'd want to cut the
thing for the CW ends of the bands. Unless you cut the antenna right at
the bottom end of the band, the harmonic resonances march up into the
bands as you move to the higher frequency bands, so I'd expect the
antenna to be too short at the CW ends of the bands on the higher bands.
E.g. if design frequency is 7.05 MHz then we're looking at 14.1 MHz,
21.15 MHz, and 28.2 MHz whereas I'm going to want to operate around
14.05, 21.05, and 28.05.

Also the high resistance and high capacitive reacance for your figures
on 80 and 20 makes me suspect that your analysis is with the loop closed
on those bands. My idea was to walk around to the back and unclip the
jumper there, so that instead of a loop, on 80 and on 30 it would be a
doublet all bent into a sloping triangle, somwhat more than a half wave
long on 80 and a bit les than 3/2 waves long on 30. I'm taking into
account end effect only at the "ends", where the two sloping wires are
now detached from each other, on 30. So the 5% shortening would only
apply to the last quarter wave on each side (ending at that low-height
insulator), not to the two half wave sections either side of the center
insulator, and since 492*2 + 468 = 1452, I'd expect the resonant length
at 10.125 MHz to be 1452/10.125 = 143.4 ft, while 1005/7.05 = 142.55 ft
would be the calculated length for a full-wave 40 m loop. So I'd expect
relatively low resistance at the feedpoint on 80 and 40, with reactance
moderately high and inductive on 80 (where it's a good bit too long for
a half-wave) and pretty low and slightly capacitive on 30 (where it's
just a bit too short for 3/2 wave).

If you ran the analysis with the loop closed on those two bands, would
you mind doing it over with the loop open?

7.05MHz 117.3 - J 0.2996 ohms closed loop
3.525MHz 9.365 + J 111.4 ohms open loop
10.125MHz 253.9 + J 60.16 ohms open loop


Those are free-space values. I forgot to put the ground in. Here they
are revised for the bottom to be about 1.3m above ground...

7.05MHz 123.6 - J 0.02019 ohms closed loop
3.525MHz 13.57 + J 105.7 ohms open loop
10.125MHz 261.7 + J 14.89 ohms open loop

And for completeness:

14.05MHz 265.2 + J 78.03 ohms closed loop
21.15MHz 181.4 + J 286.6 ohms closed loop
28.05MHz 322.6 + J 397.5 ohms closed loop

In article , John S
wrote:

If you ran the analysis with the loop closed on those two bands, would
you mind doing it over with the loop open?

7.05MHz 117.3 - J 0.2996 ohms closed loop
3.525MHz 9.365 + J 111.4 ohms open loop
10.125MHz 253.9 + J 60.16 ohms open loop


Those are free-space values. I forgot to put the ground in. Here they
are revised for the bottom to be about 1.3m above ground...

7.05MHz 123.6 - J 0.02019 ohms closed loop
3.525MHz 13.57 + J 105.7 ohms open loop
10.125MHz 261.7 + J 14.89 ohms open loop

And for completeness:

14.05MHz 265.2 + J 78.03 ohms closed loop
21.15MHz 181.4 + J 286.6 ohms closed loop
28.05MHz 322.6 + J 397.5 ohms closed loop


Many thanks. That confirms what I thought, except that I had expected
the antenna to be on the capacitive side of resonance on 30 metres. All
the figures indicate that my 142.7 ft loop is just a bit too long. The
math I did when I worked for a living was pure math, but I'm all in
favour of being experimental when doing things like this. Now that I've
got a license I'll soon be buying a rig (likely an Elecraft KX3) and
before I take the thing backpacking I'll go to a nearby park and play
with antenna lengths, running a few SWR vs. frequency curves, and come
back home and do a little calculating to see how much I want to shorten
things. It looks from your figures as if it's pretty close to resonance
on 30 metres, so I'll probably shorten it a bit so as to get it too
short on 30 and still a bit too long on 20, and equally bad SWR-wise.
That probably won't change it very much on 40, and will improve it
(slightly) on 80, where the SWR won't matter so much anyway. I'll have
to see whether it improves it very much on 15 and 10, and if not, maybe
shorten it a bit more to make them better if I can do that without
making the lower frequency bands a lot worse. I don't want to fix up 15
and 10 at the expense of making the lower frequency bands, which I'll
undoubtedly use a lot more, really bad. Maybe the best thing to do is to
build a separate antenna for 15 and 10 (and perhaps 6). Anyway, it looks
as if it's time to do some experiments.

I still wish I could do something like what EZNEC does, without going to
the trouble of either buying a PC or getting something like Parallels
(which lets one install Windows on a Mac) and then buying some version
of Windows which I wouldn't use for anything else besides EZNEC. I had
hoped that CrossOver would do the job, which it did very nicely for the
Windows exam preparation software I downloaded from the Industry Canada
and from the Radio Amateurs of Canada websites. Does anyone know of
antenna modelling software for the Mac?

David, VE7EZM

--
David Ryeburn

To send e-mail, change "netz" to "net"

On 5/25/2013 1:48 AM, David Ryeburn wrote:
In article , John S
wrote:

If you ran the analysis with the loop closed on those two bands, would
you mind doing it over with the loop open?

7.05MHz 117.3 - J 0.2996 ohms closed loop
3.525MHz 9.365 + J 111.4 ohms open loop
10.125MHz 253.9 + J 60.16 ohms open loop


Those are free-space values. I forgot to put the ground in. Here they
are revised for the bottom to be about 1.3m above ground...

7.05MHz 123.6 - J 0.02019 ohms closed loop
3.525MHz 13.57 + J 105.7 ohms open loop
10.125MHz 261.7 + J 14.89 ohms open loop

And for completeness:

14.05MHz 265.2 + J 78.03 ohms closed loop
21.15MHz 181.4 + J 286.6 ohms closed loop
28.05MHz 322.6 + J 397.5 ohms closed loop


Many thanks. That confirms what I thought, except that I had expected
the antenna to be on the capacitive side of resonance on 30 metres. All
the figures indicate that my 142.7 ft loop is just a bit too long.

Well, I didn't know your wanted to see the results with a 142.7 ft loop.
I thought you wanted to start with it resonant at 7.05MHz and let the
other figures fall where they may. Here it is repeated for 142.7ft.

3.525MHz 12.41 + J 59.12 ohms open
7.05MHz 116.3 - J 83.72 ohms closed
10.125MHz 244.3 - J 82.4 ohms open
14.05MHz 212.9 - J 78.4 ohms closed
21.15MHz 112 + J 33.87 ohms closed
28.05MHz 258 + J 77.07 ohms closed

On Fri, 24 May 2013 23:48:41 -0700, David Ryeburn
wrote:

Does anyone know of
antenna modelling software for the Mac?

http://www.w7ay.net/site/Applications/cocoaNEC/
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article , John S
wrote:

On 5/25/2013 1:48 AM, David Ryeburn wrote:

.... (snip)

Many thanks. That confirms what I thought, except that I had expected
the antenna to be on the capacitive side of resonance on 30 metres. All
the figures indicate that my 142.7 ft loop is just a bit too long.

Well, I didn't know your wanted to see the results with a 142.7 ft loop.

I thought that that would be about the resonant length for a 7.05 MHz
full-wave closed loop (1005/7.05 = 142.55). What length were you using,
for your revised figures that took into account the presence of the
ground?

I thought you wanted to start with it resonant at 7.05MHz and let the
other figures fall where they may. Here it is repeated for 142.7ft.

3.525MHz 12.41 + J 59.12 ohms open
7.05MHz 116.3 - J 83.72 ohms closed
10.125MHz 244.3 - J 82.4 ohms open
14.05MHz 212.9 - J 78.4 ohms closed
21.15MHz 112 + J 33.87 ohms closed
28.05MHz 258 + J 77.07 ohms closed

Thank you for the re-computation. These figures do make 15 and 10 better
than they were (but maybe not good enough, considering the added loss in
RG-174 at those higher frequencies). I also haven't thought about the
other two WARC bands, and I'm not particularly interested in 60 metres
where you can't QSY except in discrete steps. (And I don't think Canada
has fully implemented 60 metres for hams as yet.)


In article ,
Jeff Liebermann wrote:

On Fri, 24 May 2013 23:48:41 -0700, David Ryeburn
wrote:

Does anyone know of
antenna modelling software for the Mac?

http://www.w7ay.net/site/Applications/cocoaNEC/


I'll look into this one. Have you used cocoaNEC?

David, VE7EZM

--
David Ryeburn

To send e-mail, change "netz" to "net"

On 5/25/2013 6:30 PM, David Ryeburn wrote:
In article , John S
wrote:

On 5/25/2013 1:48 AM, David Ryeburn wrote:

... (snip)

Many thanks. That confirms what I thought, except that I had expected
the antenna to be on the capacitive side of resonance on 30 metres. All
the figures indicate that my 142.7 ft loop is just a bit too long.

Well, I didn't know your wanted to see the results with a 142.7 ft loop.

I thought that that would be about the resonant length for a 7.05 MHz
full-wave closed loop (1005/7.05 = 142.55). What length were you using,
for your revised figures that took into account the presence of the
ground?

146.555 ft

Dear David: Delighted that you are back in the game! Love your new call.
1. I have run EZNEC 5+ on a micro computer that uses Atom uP and MS XP OS.
That computer cost about $350. Even less expensive devices exist. The
computer I have can be coupled into projector (VGA) so that I can give
presentations. Pont is: Since you enjoy using math and NEC, do consider
the incremental cost of a minimal computer. Of course, I have a dedicated
computer (not ever connected to the Internet) where I do serious work much
more quickly than with the little fellow.

2. With the exception of 28 MHz (where you might wish to consider a
conventional 0.5WL dipole), I estimate that five turns of RG 174 around a
big Type 31 core will cool most of the outside-of-the-coax current. You
might have the mechanical conditions to allow two or three turns through a
small Type 31 right at the feed point.

3. When younger, I used extensive amounts of RG174 for invisible antennas.
It is possible to damage the coax, though it is strong enough to use as a
garrote.

Again, it is delightful to have you back in action. 73 Mac N8TT

------------------
David, VE7EZM

--
David Ryeburn

J. C. Mc Laughlin
Michigan U.S.A.
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