[TowerTalk] OWAs or Fans?

Thu Jun 16 19:21:07 EDT 2016

As I stated in the main post and later, just the 5 80/40 fan dipoles.  I 
used the 160 half sloper as a distance example, but neglected to say 
it's no longer in use.
The 80 and 40 meter dipoles are one single fan antenna.

I do have a 40M3-125, but I'd need to get a number of knowledgeable hams 
to assemble it and there is still the problem of getting it on top of 
the 100' 45G
The prices on RG-400 were the best I found on e-bay. 1000 feet @ $2.00 a 
foot for 1000 feet, 100 feet at 2.29 a foot from Harbour Industries.

Thanks for mentioning the RG-303. I'd not looked at RG-303.

I want chokes at the feed  points, otherwise the feed lines can pick up 
noise
I have enough 2.4", #31 cores on hand as I purchased them 100 at a time 
and I reuse them from previous chokes. If I can get RG-303 at $1.00 per 
ft, I'd just make the choke part of the feed line with no connectors needed.
With the center conductor being a copper coated, silver plated, steel 
core, I wonder how tight it could be wound, or stand up to flexing in 
the wind.

The longest lengths I found on e-bay were 100'

I haven't calculated the feed line length from the feed point, back to 
the antenna switch, yet

73

Roger (K8RI)

On 6/16/2016 Thursday 9:35 AM, Jim Thomson wrote:
> Message: 4
> Date: Wed, 15 Jun 2016 20:32:22 -0400
> From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk at tm.net>
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] OWAs or Fans?
>
> 75/80 meter slopers are very different than those on 40 and have a much
> greater imbalance.
>
> The reason why I'm considering so many cores is experience with a half
> wave, center fed, 80 meter fan which though it's a center fed dipole,
> it's highly unbalanced.
> http://www.rogerhalstead.com/ham_files/AntennaFeed2.htm When I count
> passes through the core it's actually 7 rather than 6 turns.
> With that set up, it worked well at 200 W, but as I increased the power,
> around 1 KW (maybe a little less) every LED in the system lit up.
> Instead of hanging more weight at the feed point, I added another choke
> with 5 cores and 6 turns ( wound much tighter) where the feedline
> reaches the tower. That completely cured the problem up to full power out.
>
> Because of experience and Jim's tutorial, I'm a bit skeptical of the
> really high common mode resistance claims.  5,000-7,000, I can believe.
> The photo shows two chokes, with different number of turns to get the
> frequency range which is understandable.  I only need one octave so one
> stack, with 6 or 7 turns looks good.  I could wind a single stack tight
> wound on 3 cores using RG400 to try on the fan that was a problem, or
> "bundle" the LMR400 winding that's there.  "Bundling" is easy (no, not
> that kind of Bundling) and as that choke is already there, it only
> requires lowering the antenna, which is easy with the rope and pulley
> arrangement.
> With a substantial imbalance on 75, core heating would likely be a
> problem with only two, or three cores, so my concern is with the heating
> more than the common mode Z although common mode has proven to be a problem.
>
> As I have the one antenna that is easily accessible and an AIM for
> measuring all parameters to a finer accuracy than needed, I plan on
> using this antenna as a test bed.  I definitely will try 3 and 5 cores
> with 1/8th in spacing (0.125") for cooling and tightly wound using RG-400.
> I use a milling machine to cut slots for the cores in quarter inch thick
> Lexan with 1/8th inch spacing between slots.  The slots need to be 0.003
> to 0.005" over the half inch of the core thickness so they can be
> epoxied in place.
>
> My weatherproofing gets complicated as I do not want the chokes enclosed
> because of cooling concerns.
>
> ##  How much stuff are you trying to hang off of just one tower ?   Are you planning on a 80/75/40
> sloper  plus  4 x more  1/2 wave  40m slopers  + a 160m 1/4 wave sloper ?    That’s a lot of stuff
> to hang off one tower.   The  1/4 wave 160m sloper would possibly screw up the 80m sloper.
>
> ## The oem  ARRL 5 x sloper array didnt use any baluns at all.   Dunno,  but I would consider a 1/2 wave
> sloper an unbalanced ant. Dispense with the balun at the feedpoint, and just feed the unbalanced
> slopers  with unbalanced.....coax.   Then maybe  a single CM  at the input of the switching box.
>
> ## Both danny and also Bill  hyder  N3RR  are obtaining sky high Z  with their latest CM designs, both using
> accurate test gear.  N3RRs  latest creation is > 20K, and covers  160-80-40m.   RG-303 is also teflon coax,
> and last time I looked, was aprx  $1.00  per foot.. that was a few years ago, but even then it was a lot cheaper vs
> RG-400.   Loads of goods deals on RG-400 on ebay too.   Your AIM has too much stray C to obtain legit  Z  and RS
> readings.
>
> ##  Another option, simpler, is to just use a rotary dipole on 40m.  You wont have any FB, but you will get 14+ db  of FS.
> It will also be dead flat across the band.   With your soon to be  2 x towers,  why dont you  consider a 40m yagi  + perhaps a
> 80m rotary dipole ??   Even the 80m rotary dipole would be dead flat across the entire band.   You would have a lot of fun with
> that.
>
> Jim   VE7RF
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-- 

73

Roger (K8RI)

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