[TowerTalk] ZS6BKW on 160m in a cold climate

[Mike Smith VE9AA]

Thanks Scott.  

 

All: I apologize for the non-related message tagged onto the very bottom of my original post.

We were talking about contesting and also antennas over on the MCC forum and I did a poor job editing that out.

 

I have deleted it out in this reply.

 

I will reiterate or restate in a different way, that I am not so worried about the matching on 160m.  With a little help with friends like Scott, K9MA and others here, I am sure it can be done…even in a travelling road show scenario where I’ll need wiggle room due to a different setup than home, ground conductance, height achievable etc, but my main concern is a fixed switch box at the end of the twin lead & snow/ice.  Does the 4-5’ pipe seem like a viable option?

 

I am sure there are dozens of you that have done this with dipoles, doublets etc.  but how many have done it that also get lots of ice/snow and how did you solve that without the whole thing blowing apart?

 

Tnx

 

aa

 

Mike, Coreen & Corey

Keswick Ridge, NB

 

From: K9MA [mailto:k9ma at sdellington.us] 
Sent: February 16, 2021 6:57 PM
To: Mike Smith VE9AA
Subject: Re: [TowerTalk] ZS6BKW on 160m in a cold climate

 

Hi Mike,

 

Here's what I would do:

 

First, measure the impedance at the shack end of the coax on every band on which you use the horizontal antenna. Calculate the impedance at the point where the coax connects to the twinlead, and calculate the maximum voltage at that point. If you can't find a relay that will handle that voltage, you'll have to use a knife switch and brave the snow.

 

Once you have that sorted out, install the radials, short the twinlead, and measure the impedance at that point. (If you mount the box on a pole, just run a wire from the ground where the radials converge. That won't make much difference.) Once you know that impedance, design an L network to match it to 50 Ohms. (I can help with that.) Be careful using an antenna analyzer, as AM broadcast signals may interfere with it. A sure-fire method would be to take a small variable capacitor and a tapped coil, and experimentally match it. Then measure the L and C and build an L network with larger components.

 

A friend of mine did a similar thing a little while ago, and it works fine. His matching network was about 300 pF and 28 uH, so that might be a starting point.

 

73,

Scott K9MA

 

 

 

On 2/16/2021 4:12 PM, Mike Smith VE9AA wrote:

Antenna Gurus far and wide:
 
 
 
On my 2nd radio in my contesting setup (And for travel/expedition purposes_I have a 2nd one just like it), I have a ZS6BKW (like a G5RV_) which will not work on 15m, but I added a 2nd fan dipole (for 15m) in parallel, attached to the center of the ZS6BKW and now it works on 15m too.  I’d like to add 160m for my travelling antenna and also to this antenna for my SO2R setup.
 
 
 
This dipole antenna is very roughly about 94’ long and has a 41’ (I think) 450-Ohm twinlead downlead which then attaches directly to coax…..currently I hold the twinlead/coax connection up off the ground with a rope guy line. (you’ll see why if you keep reading)
 
 
 
  Every so often I get scratching a switchbox design on paper.  I am reasonably sure I could put a few 125’ radials out on my lawn, and make a switchbox to short the twinlead together, feed the center of the coax to that as one shorted T-top element (41’ up, 94’ across the top) and then attach the braid to the 3 or 4 (or whatever) ground radials as a counterpoise/gnd system.  
 
I don’t know what the SWR would be…any guesses?
 
 
 
You’d have the leave the switchbox out there on the lawn of course, but I think with the box and 3 or 4 control wires and 3 or 4 gnd radials (more is better, obviously) you could make most any big dipole (fed with twinlead) resonate on 160m too, for a 6m-160m antenna that does most bands, right?  
 
 
 
I keep saying I am going to do it…maybe this year will be the one !....I have hesitated, not because of the work of the switchbox or radials, but I worry about the thing snapping apart in the middle of winter when the nasty weather tends to keep me inside.
 
 
 
  It bounces around in the wind up here A LOT…One end is on a tall Maple tree and the other end is on a tall slender aluminum mast (currently broken in ½, rotten ice storm)…..and with the twinlead ALMOST touching the ground, then going to coax, which is tied up off the ground, I have only broken that connection once in 5 yrs, when the twinlead froze itself into an icy top layer of the snow.
 
 
 
However with the twinlead attached to a box sitting on the ground, there would have to be lots and lots of slack and “spring” in the entire system, so when the wind blows, or ice and deep snow attaches itself to the twinlead, the whole thing doesn’t come crashing down.  I am brainstorming a couple ideas but am probably not smart enough to reinvent the wheel.  The one thing I have considered is mounting the box up on a 4 or 5’ tall pipe, above the usual snow line. I would then tie off the twinlead much as do now with rope and maybe some kind of bungy to give it some relief during winds. But then I wonder about the radials…5’ below the box.
 
 
 
Anyone have any ideas?  Consider that I live in a cold, snowy, windy, freezing-rain type climate when you respond.
 
 
 
(currently -6*C and ice pellets as I type…supposed to get a few hours of freezing rain later if it warms up a titch.
 
 
 
Thanks
 
 
 
Mike VE9AA
 
 
 
Mike, Coreen & Corey
 
Keswick Ridge, NB