[TowerTalk] Verticals above chain Link fence

[David Gilbert]

I've never been much of an advocate for just putting something up and 
trying to qualitatively decide if it works well enough.  It's a sloppy 
approach and subject to all sorts of variables we can't easily 
quantify.  But that changes significantly if there is a reference 
antenna to compare to that's far enough away to not complicate matters 
with mutual interaction, for at least you have some indication of 
relative performance.  In this case, that's probably exactly what I 
would do.

I also agree with the approach of not getting too particular about the 
radials because they are almost certainly going to be affected by 
proximity to the fence anyway ... 7 feet separation is definitely close 
enough to be problematic.  So I would just put up some counterpoise 
wires and use a matching network somewhere in the feedline ... either a 
network at the feedpoint or a tuner in the shack ...  to sort out the 
difference.  For many years at my old Scottsdale QTH I used verticals 
essentially cut to length fed against a counterpoise of a rats nest of 
random length wires  strung across the flat roof of the house.  If you 
use an array of radials cut to different lengths for each band that's 
what you're going to essentially have anyway ... as modeling will 
usually point out if you look at the impedances and current 
distributions.  I think you will drive yourself crazy trying to make 
multiple radials resonant on multiple bands by trial and error.

And no, I don't think modeling is going to  be accurate enough to handle 
multiple radials close to ground in the proximity of a chain link 
fence.  I'm a firm believer in using a tuner when one is called for.

73,
Dave   AB7E



On 10/2/2019 9:41 AM, Mark - N5OT wrote:
> Hi Ed,
>
> Do I understand correctly that you have two antennas and you are 
> asking about making changes to one of them?  If the other antenna does 
> not change, then you could compare the new unusual design to the other 
> design that has not changed, and you would know the answer.  If it was 
> me, I might be inclined to "put it up and see what happens" but be 
> advised that this approach is slovenly and without merit to some, 
> which could open you to disparaging public comment, regardless of how 
> loud your signal becomes because of the new antenna.
>
> For the humor impaired, that was a little bit of a joke really.
>
> Actually if it was me, given that you only need two resonant radials 
> to make a complete system when they are above ground, and from what I 
> understand this works when the two radials are symmetric about the 
> feedpoint, I would not be able to stop myself from digging out some 
> ribbon cable and cutting it so that I had one wire in the ribbon cable 
> per band per side that was the right length.  then I would have 
> everything I need in a single assembly with a single attachment point 
> at each end, per each side of the feedpoint.
>
> Then, I would mount it so that the radials were also symmetric about 
> the fence.
>
> Some wax poetic about tuning the radials for resonance, but I, being 
> confident the system was symmetric, would not look back at that, I 
> would cut the radials to approximate a resonant dipole, feed the whole 
> thing with a matching network located for my personal convenience, I 
> would make the radio happy with a swell SWR, and get on the air and 
> work other radio operators.  Comparing it to the other antenna could 
> yield confidence or concern, a not-inappropriate currency in my way of 
> looking at it.
>
> Bear in mind, it's possible the exact ribbon cable one uses might turn 
> out to be too small.  This is easily determined without math as 
> follows:  Put it up.  Use it.  If the ribbon cable heats up, it is too 
> small.  If the ribbon cable does not heat up, it is not too small.  
> Flames could be an indication too.  Watch the SWR while doing the 
> experiment.
>
> You might be able to do it differently than I have described and 
> achieve what some would call "better" results, which would be an 
> arguable statement, and then the argument about the results and how to 
> measure them (seasoned with comments about engineering practices), 
> would occupy the posts of this email reflector in the grand style to 
> which we have become accustomed.
>
> Or, you could do what I have described and get on the air and enjoy 
> radio contacts from your warm cozy shack during the cold winter that 
> will soon be upon us.
>
> And thanks for getting me thinking.  I might have to go outside and 
> try that.
>
> 73 - Mark N5OT
>
>
>
>
>
> On 10/1/2019 9:52 PM, ed_richardson at shaw.ca wrote:
>> Getting ready for another contesting season from my Postage stamp 
>> size City Lot.  In previous years I have installed a winter antenna 
>> (Steppir Vertical) in the rear yard as a second antenna to the tower 
>> mounted beams. In the past I have had had so-so success laying out 
>> 50-60 radials around the base of the antenna.. The problem is there 
>> is a lot of ground clutter such as trees and wooden fence in close 
>> proximity to the antenna.
>>
>> I was considering mounting the antenna about 13-15 above the ground 
>> and above a 7 foot high chain link fence. I was then planning on 
>> using 2-3 resonant radials on each band (40/30/20/15 forget about 10m).
>>
>> Has anyone had any experience with a similar configuration? Obviously 
>> keeping the radials away from the fence would be important.
>>
>> Thanks for the bandwidth!
>>
>> Ed VE4VT
>>
>>
>>
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