Dear group,

As a temporarily solution I would like to use a cheap 5/8, 6/8 or 7/8 WL
commercially available CB antenna as a non resonant vertical with elevated
radials for use on 10 - 40 meters tuned by an automatic remote ATU at the
base of the antenna. I used MMANA and EZNEC (demo) to calculate the expected
impedance for the frequency range and found too many results for the height
of the antenna. Now I am confused about what to select.
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high efficiency
and an impedance which my remote ATU can handle.

Fred, PA0FVH

Fred PA0FVH wrote:
Dear group,

As a temporarily solution I would like to use a cheap 5/8, 6/8 or 7/8 WL
commercially available CB antenna as a non resonant vertical with elevated
radials for use on 10 - 40 meters tuned by an automatic remote ATU at the
base of the antenna. I used MMANA and EZNEC (demo) to calculate the expected
impedance for the frequency range and found too many results for the height
of the antenna. Now I am confused about what to select.
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high efficiency
and an impedance which my remote ATU can handle.

Fred, PA0FVH


To a first order, you just want to avoid lengths where it's close to a
half wavelength (assuming you're using an ATU that's designed for this
sort of application) because that's where the Z is highest and toughest
to match. The low Z points are going to be easy (a few tens of ohms, and
almost any tuner can do that).

So, the lowest frequency where this is the case is where the wavelength
is 16m... straddling the 15 and 17m bands. In practice, what you might
need to do is adjust the length of the antenna by a few tens of cm one
way or the other to find a place where your tuner is happy.

Another situation is where the antenna is a full wavelength.. but 8m is
higher than the 10m ham band, so you're probably ok.

The other problem is if the reactive component gets too far for your
tuner to handle, but without knowing the tuning range of your tuner,
that's hard to know.

"Fred PA0FVH" wrote in message
...
Dear group,

As a temporarily solution I would like to use a cheap 5/8, 6/8 or 7/8 WL
commercially available CB antenna as a non resonant vertical with elevated
radials for use on 10 - 40 meters tuned by an automatic remote ATU at the
base of the antenna. I used MMANA and EZNEC (demo) to calculate the
expected impedance for the frequency range and found too many results for
the height of the antenna. Now I am confused about what to select.
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high
efficiency and an impedance which my remote ATU can handle.

Fred, PA0FVH

Hi Fred,
The first thing to understand is that for the most part the CB 5/8, 6/8, 7/8
antennas have nothing to do with the actual height. Manufacturers started
claiming these lengths because the CBers believe(d) longer is better. At
least for the mobile antennas the 5/8 etc referred more to the length of the
wire used in the antenna- electrically, they were all 1/4 wavelength
antennas.

Dale W4OP

Dale Parfitt wrote:

...
Hi Fred,
The first thing to understand is that for the most part the CB 5/8, 6/8, 7/8
antennas have nothing to do with the actual height. Manufacturers started
claiming these lengths because the CBers believe(d) longer is better. At
least for the mobile antennas the 5/8 etc referred more to the length of the
wire used in the antenna- electrically, they were all 1/4 wavelength
antennas.

Dale W4OP

The ones you looked at, it seems, were all 1/4 wavelength physically ...
electrically?

So, in you book, you can have a 1 foot, foot -- a 2 foot, foot -- a 4
foot, foot --- etc.?

Regards,
JS

On Tue, 9 Dec 2008 23:11:10 +0100, "Fred PA0FVH"
wrote:

Dear group,

As a temporarily solution I would like to use a cheap 5/8, 6/8 or 7/8 WL
commercially available CB antenna as a non resonant vertical with elevated
radials for use on 10 - 40 meters tuned by an automatic remote ATU at the
base of the antenna. I used MMANA and EZNEC (demo) to calculate the expected
impedance for the frequency range and found too many results for the height
of the antenna. Now I am confused about what to select.
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high efficiency
and an impedance which my remote ATU can handle.

Hi Fred,

6/8th and 7/8th wavelength at 10M would not have the best low angle
charateristic. At the longer wavelengths it should get progressively
better (as you may tell from EZNEC demo).

7/8th wavelength at 10M may also be hard to match with your ATU, but
worth a try.

Shorter antennas for longer wavelengths may find more loss in the ATU
than you would care to have, but a 5/8ths at 10M might be the best
work-around; and the shortest you should go.

73's
Richard Clark, KB7QHC

Hi Guys,

Thanks for your good suggestions.

The first thing to understand is that for the most part the CB 5/8, 6/8,
7/8
antennas have nothing to do with the actual height. Manufacturers started
claiming these lengths because the CBers believe(d) longer is better

The physical length of those antennas available over here are 6.5m, 9.1m and
9.5m. So any height between 6.5m and 9.5m would be possible.
It is an alternative for going to a DIY store to get aluminum tubing.

The other problem is if the reactive component gets too far for your
tuner to handle, but without knowing the tuning range of your tuner,
that's hard to know.

My remote ATU (Pi matching) has an inductance range from 0 to 63uH and the
capacitance ranges from 0 to 6300pF

Fred, PA0FVH

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"Fred PA0FVH" wrote in message
...
Dear group,

As a temporarily solution I would like to use a cheap 5/8, 6/8 or 7/8 WL
commercially available CB antenna as a non resonant vertical with elevated
radials for use on 10 - 40 meters tuned by an automatic remote ATU at the
base of the antenna. I used MMANA and EZNEC (demo) to calculate the
expected impedance for the frequency range and found too many results for
the height of the antenna. Now I am confused about what to select.
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high
efficiency and an impedance which my remote ATU can handle.

Fred, PA0FVH

------------

Obtain a Solarcon A99. It will behave exactly as you have described, even
with a built-in tuner. BTDT. Put it up about 20'. It will suck on 40 meters,
but it will work. 20 meters isn't the best either, but it is usable. 17
meters on up it will work very well.

With 100 watts I could work 15 & 17 meters into Europe from NJ in the USA,
with headroom to spare. Yes, the bands were open, but they were crowded at
the time. I worked Austria as though they were next door.

Ed, N2ECW

Fred PA0FVH wrote:
Is 5/8WL on 10meters a good height or 8 meter (22')?
What I want is a low take off angle on 20 and 30 meters with high efficiency
and an impedance which my remote ATU can handle.

Yes, you don't want to get much longer than 5/8WL on
10m and you don't want to get much shorter than 3/16WL
on 40m. 22 feet is a good compromise length. At my
previous QTH I used a 22' monopole with the feedpoint
elevated at 22' with four 22' radials sloping down
at 45 degrees (also used as guy wires) and fed with
an SG-230. It worked like a charm for transmitting -
noisy on receive. Here's some information from
simulations:

22' Monopole with 22' elevated sloping radials:

Band: Gain: Take Off Angle: Feedpoint: ~Tuner Loss
40m: 0.53 dBi: 22 deg: 24-j229 ohms: 0.9 dB
30m: 0.94 dBi: 19 deg: 46-j31 ohms: 0.2 dB
20m: 1.47 dBi: 16 deg: 128+j233 ohms: 0.1 dB
17m: 1.91 dBi: 14 deg: 556+j583 ohms: 0.2 dB
15m: 2.47 dBi: 12 deg: 1315-j372 ohms: 0.3 dB
12m: 3.40 dBi: 13 deg: 373-j560 ohms: 0.3 dB
10m: 4.21 dBi: 11 deg: 885-j290 ohms: 0.2 dB
--
73, Cecil http://www.w5dxp.com