Gary,
Thank you for the information, and for letting me know I am on the right
track. I have managed to work Europe and South America on SSB, both
with poor reports, running 600 watts. I worked US hams at about 200
miles with good reports. However, I think that I can lay much of the
blame for the reports on the fact that I have a single radial, slightly
shorter than 1/4-wavelength. Once I establish a good mechanical
connection and a reasonable SWR, I will add radials (aiming for 60) and
probably arrange for a way to change the inductance at the antenna with
a relay, for a high-end, low-end antenna. I will probably then use a
tuner in the shack to keep the output tubes happy, but I am willing to
operate into a 1.5:1 without a tuner.
The tower is 52-feet high, with a C-3 at the top. I added the coil and
got X=0 on the MFJ-259. I am also using a 4:1 balun that I had around,
since the R component is quite high. I am doing this empirically:
whatever works cheaply is what I do.
My next step is to see if I can use the hunk of (probably 75-ohm)
hardline that is lying in the back yard, instead of the 52-ohm coax I
stole from my 40-meter vertical. My only concern is that the bandwidth
seems to be far greater, and SWR lower, in the shack, implying losses.
However, I have not quantified this. The coax is hardly new, and I will
put a 50-ohm dummy load on it and see what the MFJ-259 tells me once the
wx is improved.
Your implication that even #12 wire may be small is what I had thought.
I will go to a home-improvement place and see what copper tubing might
cost, now that I have an idea of length. I would again use the 4-inch
form, but probably remove it after winding the tubing to leave only air
dielectric.
I am quite heartened by this, and I am even dreaming of home-brewing
matching networks in the future. With the MFJ analyzer, I could even
match to 75-ohm coax, bring it into the shack, and then reconvert to 50
ohms with a tuner or another fixed matching network. I can used fixed
capacitors when I know what values I am looking for, so those costs can
be kept low. The wire investment was $4.00 and the coil is over twice as
long as I needed. The PVC is less than $10.00 for ten feet.
I suppose my next step is learning how to blow glass for amplifier tubes.
73,
Jan, KX2A
K9AY wrote:
> Jan,
>
> You did the #1 best thing by using a large diameter. Any improvements
> with a neater winding will be small. Same goes for larger wire or
> tubing -- the theoretical improvement may be hard to see.
>
> The only exception would be a coil with a lot of current flowing
> through it. In that case, a larger conductor and optimum
> length/diameter ratio for best Q would reduce the losses.
>
> Actually, I'm a little surprised that you need inductance with a shunt
> feed -- is the tower short?
>
> 73, Gary
> K9AY
>
>
>
>> I began work on shunt loading my tower for 80 and/or 160. The initial
>> reading on my MFJ 259 showed that the antenna was too short, and it
>> needed a coil in series to get X=0. I went to a plumbing shop and found
>> solid #12 insulated wire, wrapped it around some 4-inch diameter PVC
>> pipe, and lo and behold, I am in the ballpark.
>>
>> My question is: I intend to re-wrap the wire so it is neat, but what
>> kind of problems should I expect from this kluge coil? I tried moving
>> the turns around, with the ends fixed in place, and there is almost no
>> change in X on the 259. Am I looking at low efficiency, potential
>> arcing, other problems associated with such a cavalier method of
>> creating a coil?
>>
>> Jan, KX2A
>> _______________________________________________
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>> Antennaware@contesting.com
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>>
>
>
>
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