Hi
Can someone advise me of dimensions for a 40 meter version?

Here is original article:
http://www.hamuniverse.com/cobraantenna.html
Thanks
Jim K2TL

wrote:
Can someone advise me of dimensions for a 40 meter version?

The 80m version is 1/2 the size of the 160m version.
The 40m version would be 1/2 the size of the 80m version.
--
73, Cecil, http://www.qsl.net/w5dxp

Hi
Well, not exactly, but close. A half wave on 160 is 260 feet, half of
that is not 140 as in the Cobra and 80 meters half wave is about 134
feet, so half of that is not 70 feet, as in the Cobra antenna. But its
a good enough starting point to work with I suppose. Maybe I'll try 35
feet for 40 meters.
Thanks
Jim

Oh wait, I see what you mean..you are correct Hi..So, 35 feet would be
correct anyway.

Thanks

wrote:
Oh wait, I see what you mean..you are correct Hi..So, 35 feet would be
correct anyway.

A word of caution about scaling of this antenna. Assuming that
the 70 ft. version does work on all HF bands, 80m scales to
40m, 40m scales to 20m, 30m scales to 15m, and 20m scales
to 10m. As you can see, scaling from an 80m version to a 40m
version doesn't necessarily cover the WARC bands.
--
73, Cecil, http://www.qsl.net/w5dxp

Thanks for the replies...I am trying to construct a multiband antenna
for a disabled friend who lives in a Townhouse. He has some room up in
the attic. I think I could squeez a 35 foot lnear loaded inverted vee
up. Its going to be fed with 300 ohm line. If it works, fine, if not,
then its butterfly collecting for him instead of Ham Radio. Hey, its
worth a try. Some of the reviews I have read are interesting. BTW, DX
Engineering sells 2 models of this antenna using 3 conductor power
cable and 300 ohm line. Check thier site. They even let you read the
manual in PDF.
Jim

wrote:

Well, not exactly, but close. A half wave on 160 is 260 feet, half of
that is not 140 as in the Cobra and 80 meters half wave is about 134
feet, so half of that is not 70 feet, as in the Cobra antenna. But its
a good enough starting point to work with I suppose. Maybe I'll try 35
feet for 40 meters.

I didn't say anything about wavelength. The 140 ft. Cobra is alleged
to work on 160m. The 70 ft. Cobra is alleged to work on 80m. So a
35 ft. Cobra would be alleged to work on 40m.

Incidentally, I just modeled a 124 ft. Cobra version that has
performance on 160m that is superior to the 140 ft. version
because the SWR on the 450 ohm feedline drops from about 63:1
to about 47:1 according to EZNEC. Performance is comparable to
a 124 ft. dipole on all HF bands. This looks like a fairly
reasonable way to obtain 160m performance from a 124 ft. antenna.
--
73, Cecil, http://www.qsl.net/w5dxp

Don't know what a Cobra is.

But a 124-feet (38 metres) dipole, at a height of 40 feet (12 metres)
in conjunction with 60 feet (18 metres) of 450-ohm ladder line and an
L-match tuner has the following characteristics -

Freq MHZ Loss relative to ideal
1.9 8 dB
3.8 0.5 dB
7.1 0.9 dB
10.1 0.8 dB
14.1 0.6 dB
21.1 0.6 dB
29.0 0.6 dB

Loss includes, antenna, line, tuner and ground.

Data obtained using program DIPOLE3 from website below.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Reg Edwards wrote:
Don't know what a Cobra is.

It's a linear loaded folding shaped like this for 1/2 of the antenna:

62 feet per side
---------------------------------------+
|
+--------------------------------------+
|
+----------------------------------------FP--- other side

Freq MHZ Loss relative to ideal
1.9 8 dB

The above antenna doesn't have nearly that amount of loss on 160m.
--
73, Cecil http://www.qsl.net/w5dxp

The website states 73 feet for the 40 meter version that can also be used on
80. One would then assume that a 20 meter version 36.5 feet would also work
on 40.

"Cecil Moore" wrote in message
. com...
wrote:
Can someone advise me of dimensions for a 40 meter version?

The 80m version is 1/2 the size of the 160m version.
The 40m version would be 1/2 the size of the 80m version.
--
73, Cecil, http://www.qsl.net/w5dxp