Best Way to Make a 1/4-Wave Reference Wire?

[CRAIG W BEHRENS]

I'm fooling around with custom portable Vertical array antennas for portable and DXpedition use.
I was wondering if anyone in our list Brain trust had a favorite way to cut wires to a (reasonably precise) 1/4-wave length.
(Yes, I can measure and No I don't want to model, I want to field test and calibrate.)
What I want to do is have an elevated vertical (say base at 8'-10'), and add a temporary 1/4-wave "reference" counterpoise wire with a 20-degree downward slope.
Then, use this set-up to adjust whatever physical items I'm using for the vertical element to get a 1:1 match, calibrated to the radials length.
I want to end-up with a balanced antenna that is resonant and does not require a tuner (given that I'll have some minor adjustments to fine-tune the antenna's match at different locations).
So, theoretically, the vertical could be made of 6-inch diameter aluminum tubing (not likely in the field), insulated or non-insulated wire of any size, or whatever.
I'm also curious about and I to be able to see what the differences are in the lengths of antennas based on what materials of different types and sizes that I use.
Ideas???
Thanks.

72/73,
Craig W. Behrens--NM4TK3, KX3, K2, K1 +++    
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[JHRichards]

Interesting project.   My generalist, non-expert suggestion.  There are
many variables you must consider, not the least of which are the
electrical properties of the components, such as the length, velocity
factor, diameter, resistance in circular mils, inherent impedance and
capacitance of any conductor or radiator, the effects of any dielectric
present, capacitive and inductive coupling with other objects in the
vicinity, and many other factors.

I am a big fan of verticals, but I usually work in the other direction:
  I set the length of the vertical element, and adjust the length and
angle of the radials to effect a good match, but, it sounds like you
want a set, or multiple sets, of known radials as an ersatz control
group, against which you will judge the effects of different vertical
radiators.

I suggest you consider and measure / record all the factors you can, and
build a set of control radials for your experiments, and use them for
each individual experiment, and see what happens.  You cannot control or
account for all factors, but unless you start someplace, you will go no
place.  Build a set of radials and use them as a reference, and see what
you get... assess the data... regroup... re-formulate ... and determine
what to do next.

I suspect the guy to ask is Rudy Severns, N6LF, who is the guru of
vertical antenna testing.

Happy days, good luck.

--------------------  JHR -------------------------


On 7/26/2014 9:27 AM, CRAIG W BEHRENS wrote:  curious about and I to be
able to see what the differences are in the lengths of antennas based on
what materials of different types and sizes that I use.
   
 > _____________________________________________________


On 7/26/2014 9:27 AM, CRAIG W BEHRENS wrote:

> I'm fooling around with custom portable Vertical array antennas for portable and DXpedition use.
> I was wondering if anyone in our list Brain trust had a favorite way to cut wires to a (reasonably precise) 1/4-wave length.
> (Yes, I can measure and No I don't want to model, I want to field test and calibrate.)
> What I want to do is have an elevated vertical (say base at 8'-10'), and add a temporary 1/4-wave "reference" counterpoise wire with a 20-degree downward slope.
> Then, use this set-up to adjust whatever physical items I'm using for the vertical element to get a 1:1 match, calibrated to the radials length.
> I want to end-up with a balanced antenna that is resonant and does not require a tuner (given that I'll have some minor adjustments to fine-tune the antenna's match at different locations).
> So, theoretically, the vertical could be made of 6-inch diameter aluminum tubing (not likely in the field), insulated or non-insulated wire of any size, or whatever.
> I'm also curious about and I to be able to see what the differences are in the lengths of antennas based on what materials of different types and sizes that I use.
> Ideas???
> Thanks.
>
> 72/73,
> Craig W. Behrens--NM4TK3, KX3, K2, K1 +++  
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[John Oppenheimer]

Hi Craig,

What you are describing is an antenna in the dipole class, an antenna
with two poles. Similar to an inverted vee rotated by 225 degrees. The
half wavelength for the sum of the two elements will determine the
resonant frequency. The total length will be near the classic 468/MHz =
length in feet.

The easy way is to make the antenna a little longer, measure the
resonant frequency with an antenna analyzer, then scale to the desired
frequency, for example, for 14.05 MHz.

468 / 14.05 = 33.3' make each element 1/2 of 33.3' plus about a foot, or
17.5' each. Using an antenna analyzer, measure the resonant frequency,
it should be close to 13.4 MHz. Divide the measured frequency by the
desired frequency, for example 13.4 / 14.05 = 0.954. Multiply the start
lengths by the ratio, 17.5 * 0.954 = 16.7' for each of the two lengths.

The above antenna will require a current mode Balun, for example the
Elecraft BL2.

Also, when modeling the gain pattern, it has about a 3 dB front to back
gain ratio. The front being the side with the horizontal wire.

I hope this helps,
John KN5L

On 07/26/2014 08:27 AM, CRAIG W BEHRENS wrote:
> What I want to do is have an elevated vertical (say base at 8'-10'), and add a temporary 1/4-wave "reference" counterpoise wire with a 20-degree downward slope.
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[Don Wilhelm-4]

Craig,

OK, so you want to have an electrical quarterwave resonator and
electrical quarterwave radials.

I would suggest that you first cut two radials - make them a bit long
and put them up at the height and slope that they will eventually be
used.  Connect these two radials as you would a dipole - then measure
the resonant frequency.  Adjust the length as needed to resonate at your
desired frequency.
Note that these wires being close to the ground will not conform to the
usual "cutting formula" of 486/frequency in MHz, so start plenty long.  
Trim the same amount from each end to keep both radials the same
length.  You should now have 2 wires each an electrical quarterwave long
in the position they are to be mounted.

Once you have those two radials tuned - disconnect the one connected to
the coax center conductor (leave the one connected to the coax braid).  
Connect the center conductor to the vertical radiator and adjust the
radiator length for resonance.
You will find this procedure in ON4UN's Low Band DXing book.  He does
use a buried radial field to adjust the length of the radiator, but I
assume you do not have one of those handy.

OK, you have the vertical and one radial tuned for certain - remove that
radial and check that the other radial is also correctly tuned - adjust
its length as needed.

If you plan more than 2 radials, tune each of them (one at a time) to
resonate with the previously tuned vertical.  When all have been tuned,
you may connect all the radials together.

If you want a simplified process that yields essentially the same
results (for practical purposes) - put up the vertical radiator cut to
the normal formula.  It may not be exactly a quarter wave, but it will
be 'close enough' - yes it may produce something like a slightly
off-center fed system, but it will not be so far off center to make much
difference.
Now connecting each radial (again one at a time) trim the length of the
radial to make the resonance point at the frequency you desire.
Disconnect that first one and continue with all the other radials
planned.  When finished with all of them, connect all the radials together.

That is my standard procedure for tuning elevated radials.  With
elevated radials, only 2 are required to cancel the horizontally
polarized radiation - if they are placed 180 degrees apart.

73,
Don W3FPR


On 7/26/2014 9:27 AM, CRAIG W BEHRENS wrote:
> I'm fooling around with custom portable Vertical array antennas for portable and DXpedition use.
> I was wondering if anyone in our list Brain trust had a favorite way to cut wires to a (reasonably precise) 1/4-wave length.
> (Yes, I can measure and No I don't want to model, I want to field test and calibrate.)
> What I want to do is have an elevated vertical (say base at 8'-10'), and add a temporary 1/4-wave "reference" counterpoise wire with a 20-degree downward slope.
> Then, use this set-up to adjust whatever physical items I'm using for the vertical element to get a 1:1 match, calibrated to the radials length.
> I want to end-up with a balanced antenna that is resonant and does not require a tuner (given that I'll have some minor adjustments to fine-tune the antenna's match at different locations).
> So, theoretically, the vertical could be made of 6-inch diameter aluminum tubing (not likely in the field), insulated or non-insulated wire of any size, or whatever.
> I'm also curious about and I to be able to see what the differences are in the lengths of antennas based on what materials of different types and sizes that I use.
>

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