Thursday 13 May 2021

Going simple.

In this month's Practical Wireless, there's a nice review by G3UGF of what is actually a very simple new product: the Ampro portable kit.

It's nothing more than a collection of different band sticks, which fit onto a vehicle-type mount, clamped to a solid earth rod.  The idea being that it's all simply a stick-it-in-the-ground, cheap antenna that might also be effective.  

Carrying sticks is easy, but the stainless element at the top is very springy, and becomes very irritating when walking any distance.  But that's a minor point, really.

It's certainly a great way to sell more Ampro sticks, which are actually very well-made; I have several for the car already.  

But the price!  How much for eight sticks, a clamp and a copper rod?  £238, reduced in some outlets to 'just' £199.99!  I suspect most of us will buy only the sticks we really want (80m is a bit wishful thinking for good performance at this size, for example), make our own ground rod, like I did (it's not ideal, copper tube is too soft at this kind of length, unless you have soft ground or sand), and buy or make the mount separately. 

Very simple, but you do need radials. 

I never thought of making exactly this type of antenna, but I did come close some years ago, with a manpack.

So, I went to get my manpack from a remote shack in the fields that I have; it's been unused for a couple of years now.  There was a drama underway, as some cows had escaped into the main road!  After all that was sorted out, I made a simple copper tube mount with a short 90 degree leg to attach the type of clamp I already had.

Unlike my manpack, proper matching (at 14MHz) was not possible without the addition of two 1/4 wave radials.  With the radials, I got down below 1.09:1. 

Great stealth antenna, with very good performance.  WSPR tests at 14MHz.

Excellent match for much of the 14MHz band (scale is too wide - my fault!)

How did it do on 200mW WSPR?  Surprisingly well, despite horrendous HF conditions in a G3 storm.  I can't remember what antenna the other guy has, but he is a good UK station (reduced duration relative to the other comparisons - he didn't keep going as long!):


Here's another - again no idea what antenna, and the other guy is using 500mW, against my 200mW (40h of testing):


And, finally, another 200mW:200mW comparison (40h duration), at which point I think we can safely conclude that the Ampro stick-and-ground rod system leaves nothing to be desired:

Distances are only one element of performance.  Also important to consider relative signal strengths.  Here's one comparison across all distances.  Antenna is described as follows: "TX antenna is 1/2 wave end fed wire against a short counterpoise with a tuned matching transformer on T82-2 core."

Essentially identical performance against G7CKX across all receiver distances.

And at DX distances, beyond 5010km:

Only 1.9dB down, on average, against the end-fed.

 

This antenna is a bit of a compromise, obviously.  It works well for its size, simplicty and pocket-money cost of building or buying.  It's surprisingly stable in a good wind, too.  Even if you have to carry, say, three whips along with you, it's always going to be a lot less hassle than tuning a magnetic loop.  Once your whips and radials are set-up properly, you just stick and go!


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