Monday, 3 April 2017

HF Manpack Success!

I like the convenience of operating from home, where I have a modest, 'kitchen-top' station.

But, using one's home as a radio sation can be intrusive on other members of the family.  It can also be far too much like putting all your eggs in one basket if EMC issues develop in the neighbourhood.

So, I've always kept my hand in simple, rapid deployment of HF radio away from the home, so that, whatever comes to blight me there can be avoided simply by getting in the car and visiting a hill or beach.

My most recent incentive to go portable in earnest came a couple of weeks ago, when a neighbour installed an electric fence right up to my boundary.  Whilst noise blanking gets rid of the ticking almost all the time, and the fence is not that noisy anyway, it does show how easily and quickly neighbour EMC problems can come to influence and possibly spoil your home station.

So, I took some inspiration from a few images under a Google search for 'HF manpack'. These were all much the same, copper tube constructions that contain all the equipment and are either backpacks in their own right, or otherwise slip into a fabric rucksack.

WSPRlite testing of the copper tube manpack.


I was interested to see whether I could reach any sort of workable match of the tube frame when I mounted a 20m mobile whip on top of it, using a gutter mount, but no ATU.  A quick connection to my SARK-110 antenna analyser showed that, indeed, a perfect and relatively broad match could be achieved quite easily, simply by adjusting the whip length as normal.

Armed with quite a positive first indication from the analyser, I set the frame out in the garden and hooked-up my WSPRlite QRP transmitter, running 200mW.

I left the unit running all day whilst I was out, but conditions were so poor in an R2 blackout that I had no spots at all!  That changed the following day, when conditions relented somewhat, and good distances out to Finland during the day were being achieved.  Later, a few spots out to Russia and the US were reported.

I can tell the bakcpack is working well because, thanks to DXPlorer, the software that comes with WSPRlite, I can compare with known, efficient stations elsewhere in the UK and see that it is as good as, for example, a full wave horizontal loop.  More time is needed for a full assessment.

Clearly, this frame is a workable and efficient solution to not only going mobile but backpack (or pedestrian) mobile, all at very little cost.  Those who operate /PM from the beaches of the UK on a regular basis know how they can manage QRP contacts with VK and ZL very easily, whilst folks at home can't even hear the antipodes!

I'm looking forward to grabbing an FT857 or similar rig, and enjoying morning and evening sessions down the beaches.  Imagine, no noisy solar PV, plasma screens, LCD lights or electric fences anywhere in sight!

UPDATE!

Here are some results from WSPRlite testing.

First, a comparison with a horizontal, large loop antenna:


Next, a comparison with a doublet:


And, finally, against a trapped dipole:



Update 2:

I've now assembled my TS-480 and a 12Ah battery onto the frame.  It's comfortably backpackable, having bought some shoulder straps for it.  The overall experience of using the system on SSB is pretty much identical to operating from a car with a magmount, so I'm pretty happy with that.

The battery is small, but provides enough duration to enable me to cover plenty of overs during the 20-30 minutes of peak long path propagation.  On about 15-20W peak output, I've managed Russia and the mid-west US so far, as well as the usual lot of easy EU stations.  Overall, it is working as well as such a system can be expected to.

An obvious improvement in terms of power duration and ease of transport would be to install the system around a decent, large-wheeled all-terrain pushchair.  Sadly, I sold ours years ago, and that model, which was perfect, is either difficult to find and/or very expensive now.If you go down this route, avoid, at all costs, those buggies with front wheels that swivel, and wheels that are either too narrow, too small, or both!  Wheels needs to be at least 12" in diameter to cope with sand and rough surfaces well.


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