Topband: ZS6BKW(G5RV) on 160m?

[kolson at rcn.com]

The ZS6BKW is really a quite different antenna than a G5RV. On 40, 20, 18, 12 and 10 meters, the feedpoint is close enough to 50 ohms to present a good match when properly trimmed . The coax is matched so  the length of the coax is not important and losses are low ON THESE BANDS. To be fair, the original G5RV was designed as a 20 meter antenna prima rily and it works only after a fashion on the other bands (as G3OIT found) due to losses in the unmatched coax, for the most part. With the ZS6BKW here, I switch from the coax to ladder line back to the shack at the feedpoint as G3OIT does on the unmatched bands (80, 30 and 15) . On 160, I short the ladder at the feedpoint and feed it through a matching network against a radial system. 

Best, Kevin K3OX 

----- Original Message -----

From: "Keith Jillings (G3OIT)" <g3oit.keith at jillings.org.uk> 
To: "Mike Smith VE9AA" <ve9aa at nbnet.nb.ca>, topband at contesting.com 
Sent: Thursday, March 26, 2015 6:51:49 PM 
Subject: Re: Topband: ZS6BKW(G5RV) on 160m? 

On 26/03/2015 21:12, Mike Smith VE9AA wrote: 

> This is great info.  Hey, thanks guys,.////As I read these comments, I am now wondering if there is a magic length of coax, that attaches to the 40’ of  450 ladder line that I could short right in/at the improvised vacation shack end, or just at the interface to the door/window/outside world, where I will be allowed to bring the coax in the (for lack of a better term), “cottage”….? 
> 
> It’s a long story, but I am thinking I am going to be limited to one antenna, and there may not be any more than one coax, and no going in and out the building in the wee hours of the morning.  A restrictive scenario, but you’ll just have to trust me. 
> 
> So, if I could have, let’s say…..10’ of coax in the “shack”, then let’s just say for example, 40’ feet of coax and then the 40’ of ladder line, could I short the coax 10’ from the rig in the shack (and even add a coil ?), then if I wanted to get back on the other bands, simply unshort the 10’ run and put everything as normal?  My goal would be to work some W1’s/W2’s/VE3’s and perhaps a G/EA, Carib? on 160m just for mults.  I’d rather not carry too much gear with me, so if I could get it in the ballpark and let the Icom’s internal tuner handle a small mismatch, I’d be OK with that.  I might even rethink the 2 gnd radials and tie into the cottage gnd, but whatever works.  I’m not clear yet what the trip hazard ratio will be where I am at. 

Hi Mike, 

I haven't quite got my head round what you're planning, but what I'm 
doing may give you some ideas... 

A G5RV is a compromise antenna.  It's based round a doublet fed with 
ladderline, and a coaxial feed that sort-of matches it.   It works, sort-of. 

I had one here.  I wasn't impressed with the performance.  I removed the 
coax, brought the ribbon feeder into the shack, and built a matching 
unit using a roller inductor, switched variable and fixed capacitors, 
and air-cored baluns.  I tried a "broadband" ferrite balun, but it got 
very hot on some bands.  The air ones don't even get warm. 

Getting rid of the G5RV coax improved performance significantly - I can 
get an indicated 1:1 match on all the HF bands on the input to the 
matching unit.  I don't know how well it's performing overall since I 
don't have the measuring equipment, but it does well in pileups and I 
seem to be able to work stuff.  It takes a while to retune when I change 
band, but I'm not in a hurry.   I have all the settings written down. 

On 160, I strap the ribbon feeder and load the whole antenna as a "T", 
tuned against ground.  I live in a house built around 1490 and there are 
all kinds of restrictions on what I'm allowed to do, but nobody knows 
about the radial field that runs round the garden, across the lawn, etc 
- about half an inch below the surface.   The antenna runs between three 
trees, with a telescopic pole hidden in the middle one to get the 
feedpoint above the treetop.   I need to do some more experimenting with 
it on 160.  I can work all of Europe and into Africa and Asia, but I'm 
definitely in the "little pistol" category on top band.  I don't think 
there's a better solution given the restrictions of the listed property. 

Best of luck - hope maybe we will work on 160! 

Best 73, 

Keith  G3OIT 

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