Joe
Thank you.
Yes I agree. I've got PVC insulator arms that I've already bought fittings for
them that will allow me to create a three wire cage spaced any distance I'd
like. I presume the cage should be similar in width as the Skyneedle. Say 10"
to 12" width.
Thanks and I'll keep u posted.
Carl AG6X
Sent from my iPhone
> On Feb 14, 2014, at 3:44 PM, "Joe Subich, W4TV" <lists@subich.com> wrote:
>
>
> > Is the single 14AWG too thin causing goofy readings?
>
> Absolutely! Treating the Sky Needle and the #12 wire as a folded
> dipole and using 8" for the diameter of the tower, you have a 16:1
> step-up with the single #14 wire.
>
> If you made a cage of 4 or 6 wires with a 6 to 8" diameter, back of
> the envelope calculations say the impedance with the 67' tap point
> would be much closer to 50 Ohms *and* the bandwidth would be much
> wider. Even three parallel wires spaced 12" or so would have a much
> greater effective diameter and would reduce the step-up you see by
> a great deal.
>
> Of course, if all you can do is a single #14 wire, use an Omega
> match or an L-network to bring the impedance down to 50 Ohms.
>
> 73,
>
> ... Joe, W4TV
>
>
>> On 2/14/2014 6:14 PM, Carl Braun wrote:
>> List
>>
>> Some of you may have followed my efforts in trying to shunt feed my
>> 90' Tri-Ex Skyneedle with 20 meter yagi at 93'. I'm still unable to
>> find any sort of resonance point on the tower. To refresh everyone's
>> memory here are the specifics:
>>
>> 90' Skyneedle that is 12" round at the base and 4" round at the top
>>
>> 13' of mast out the top
>>
>> 5 element Telrex 20M monobander mounted at the 93' level. No other
>> antennas on the tower
>>
>> 1 ½" copper pipe as a radial ring that surrounds the concrete base
>> that measures 4' x 8' rectangle. Three 8' ground rods are connected
>> to the radial ring via 1" copper strap that is .125 thick.
>>
>> Currently I have 27 14AWG insulated wire radials. Most of the
>> radials are 20' to 50' long with three at 90 to 120' long and four of
>> them connected to my 40M vertical array which have 100 count radials
>> 50' to 100' each.
>>
>> The tower is grounded to each ground rod via 1" copper strap .125"
>> thick and, as mentioned above, the ground rods are connected to the
>> radial ring with the same strap with copper clad stainless screws.
>>
>> When I bolted the gamma arm to the tower at the 90' height I dropped
>> a single 14AWG wire to the ground where my FLUKE meter read ZERO ohms
>> between the radial ring and the end of the gamma wire with no
>> fluctuations so I'm confident that I have good continuity throughout
>> the tower.
>>
>> Here are the readings that I saw on the MFJ analyzer with the gamma
>> arm mounted at the (4) points on the tower that are available...
>>
>> With the gamma arm mounted at 90' and 36" spacing I saw 425 ohms at
>> the end of the drop wire on the MFJ
>>
>> With the gamma arm mounted at 67' and 36" spacing I saw 380 ohms at
>> the end of the drop wire on the MFJ
>>
>> With the gamma arm mounted at 46' and 36" spacing I saw 240 ohms at
>> the end of the drop wire on the MFJ
>>
>> With the gamma arm mounted at 28' and 36" spacing I saw 120 ohms at
>> the end of the drop wire on the MFJ
>>
>> At all of these points I was able to knock down the R with my honkin'
>> 1050pf cap to some resonance sort of resonance at 1.825 MHz but, as
>> most everyone has indicated, I should be able to find a 50 ohm tap
>> somewhere on the tower. I can't find it.
>>
>> When I had the gamma arm mounted at the 90' level. I was able to put
>> my baby variable 160pf inline to bring the 425 ohm impedance down to
>> about 60 ohms and the antenna heard very well; especially on the 1700
>> KHz broadcast band, with a 2.4:1 Vswr. Similar results could be seen
>> at the other levels too as long as I brought the R down with a
>> variable cap. Yesterday, with the gamma arm at the 46' level (and
>> 240 ohms on the MFJ) I was able to put the big variable inline to
>> bring the reading to 24 ohms with a TRUE X=0. With a 22 ohm to 50
>> ohm UNUN, I saw 1.3:1 Vswr on the output of the UNUN. I worked a W2
>> in NJ and a W4 in Florida with just the 1000D. BUT...again...I'm
>> bringing the R down with the capacitor...not finding 50 ohms anywhere
>> on the tower.
>>
>> Is my radial field so poor that I'm seeing these goofy readings?
>>
>> Is the single 14AWG too thin causing goofy readings?
>>
>> I'm back to scratching my head.
>>
>> Comments from the list?
>>
>>
>>
>> Carl AG6X
>>
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