Discussion in 'Amateur Radio News' started by KX4O, Jul 9, 2020.
Groovy Mahn...Real Groovy
Me I do prefer the Slim Jim easy and short that a J-pole and is adjustable for for where you want or need to
oparate does not fall all over and less wind and storm damage have used for many years and no maintance free fpo more than
20 years look here http://www.hamuniverse.com/slimjim.html it just keep working build 1 and build with good stuff ever in to pvc tube with 300 ohm tape,
ZL 1 PDT / ex ZS1PDT
Years ago a friend's vhf marine antenna took a lightning hit...at her home in The Bahamas. She wanted to replace it...and damn near fainted when she saw what a new one costs. I built her a "temp" replacement ground plane using an SO239 coax panel connector and some copper welding rod. Whole thing took about 30 minutes and cost about $5.00. Hoisted it up on a PVC pipe...fed it with RG-8 coax...and...presto. I read with some amusement in QST and elsewhere all these antennas to be built...complicated....hard to get tuned right. KISS....it works.
I would never replace a 1/2 wave VHF marine antenna with a 1/4 wave groundplane. Your life may depend on it. A 1/2 wave radiates nearly horizontal while a 1/4 wave GP radiates some 30 degrees upwards, giving you much less range.
I recently built a 1/4 wave GP for 23cm just for fun and I noticed that I could only work a specific repeater 20 miles away when I tilted the antenna downwards in the direction of the repeater. Vertically, I could not reach it.
Just cough up the $50 and be safe!
If a 1/2 wave has more gain than a 1/4 wave due to a narrower vertical pattern, wouldn't the boat healing reduce the effectiveness of the 1/2 wave?
That's a good question especially for single hull sail boats. I'd say the patterns of both are so broad and similar that this won't matter for all, but the most serious angles. Here is a comparison (measured) of two 1/4 wave approaches with a J (half-wave)...
I think the takeaway here is boat healing, while an important consideration, won't be a big deal until you have some collinear gain of some sort. Here's an example where antenna tilt begins to matter. Your question is perfectly reasonable. I think we are reasonably safe with either a 1/4 or 1/2 wave vertical antenna with respect to boat healing.
In your reference, it looks like about 30 degrees (or so) angle of heel, there would be nulls. I'd love to see the real effect on range of different antennas on sailboats, given that height is probably the dominant factor in range and a larger antenna puts weight at the top of a mast and affects the boat itself.
For example compare a duckie that's mounted just under the masthead light (lets say 30' to 45', and a 5/8 wave mounted 6' above the water (with either a gimbel mount or hard mounted), at 30 degrees of heel or so (which would only affect the non gimbel-ed antennas).
Not that any of this matters to me, I'm more of a canoe person, but it's a god thought exercise.
Never been a fan of this design to begin with, less so of the occasionally ludicrous performance claims.
That said, it seems like someone didn't research this well when it comes to patents. As mentioned by others, decoupling of a J-Pole isn't anything new, nor is feeding the feed-line inside the copper. But then we seem to be talking about a government agency so... whatever.