[TowerTalk] Broadbanding 80 meter dipole

[Grant Saviers]

The ARRL Antenna Handbook has a number ways to broadband a dipole, 
several probably difficult as noted.

One not in the current handbook is the Witt/Leeson tuned coaxial 
resonator feed method,  see 
http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1993/09/page27/index.html

At QRO on 80m, small coax such a Davis RG8X-LL will be ok and RG6 is QRO 
capable for the 75 ohm section per W8JI evaluations.  There are no L, C 
or relays in the air, it's a plain wire dipole and the coax is needed 
anyway to feed it, so it is cheap, light, and easy to maintain.

I've built one with RG8X-LL and Belden 8281 double shield video cable 
(often cheap on ebay) for next year Field Day but not run the in the air 
swr curves yet.   As with any dipole there is height sensitivity so for 
this application modeling with the tower is a good idea.  I modeled it 
for my application with EZNEC/4 and optimized it with AutoEZ and the swr 
is < 1.6:1 from 3.5 to 3.92Mhz, rising to 2:1 at 4.0MHz.

Grant KZ1W

On 8/18/2017 0:56 AM, Roger (K8RI) on TT wrote:
> I'd need 5 auto tuners and the configuration would require that the be 
> close to in sync.
> These are center fed, half wave dipoles.  I've had excellent results 
> on 40 and 75.  Unfortunately with the common mode choke and BuryFlex 
> hanging from the center. It requires a LOT of tension to keep the 
> antennas straight...About 200# worth.  There's a lot of 5/16ths double 
> braid rope already on the tower through pulleys, making working on the 
> antennas easy, but I don't think the 5 auto tuners would be practical.
>
> 73, Roger (K8RI) .
>
> On 8/17/2017 Thursday 3:20 PM, Rod Greene wrote:
>> Or use an auto tuner at the feedpoint to match the slopers on 
>> whatever band/freq you want to use. That's what I do.
>>
>> 73, Rod/w7zrc
>>
>>
>> ------------------------------------------------------------------------
>> *From:* Roger (K8RI) on TT <K8RI-on-TowerTalk at tm.net>
>> *To:* "towertalk at contesting.com" <towertalk at contesting.com>
>> *Sent:* Thursday, August 17, 2017 12:33 PM
>> *Subject:* [TowerTalk] Broadbanding 80 meter dipole
>>
>> I've seen a few possibilities in the past, but I'd like to add a dew
>> slopers to come up with the 5 used for some directivity, gain and front
>> to back. Switched coils at the feedpoint with frequency sensing would
>> likely work.  I've had excellent results with just a couple switched
>> slopers on 40.
>>
>> To complicate things I'd like to do this and maintain the dual band 75 /
>> 40 meter operation, which would likely require separate feedlines. The
>> unused line would / could end up as a stub.  I could possibly use the
>> frequency sensing to disconnect the coax for the unused band.
>>
>> Thoughts?
>>
>> -- 
>>
>> 73
>>
>> Roger (K8RI)
>>
>>
>> ---
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