WSPR – propagation and antenna tool

Ok so you’ve put up a new antenna and wonder if its going to work out any better than the one it replaced. It produces a lot of noise on receive and the stations sound louder but does that mean its any better. Do you sit on a band tuning up and down calling stations hoping for a reply or wait for the next contest where all the reports will be 59.

What you really need is a way of sending out a low power automated transmission and (hopefully) receiving a virtually instant reply from a distant station giving your received signal strength, both station locators and distance, and recording it for later analysis on an online database - well, now you can using a piece of software from K1JT called WSPR (short for whisper).

There is no point in me going over much that has already been said about WSPR so the best thing to do is visit http://www.g4ilo.com/wspr.html which has an excellent introduction to the system and follow that up with a visit to http://wsprnet.org/drupal/

Have a look at the map and database and especially the database column showing the output power being used – its amazing how far qrp will reach.

Using a capacity hat(s) to improve efficiency

The radiation efficiency of the Hi-Q 5/160 antenna is as follows and is based on a 102" whip mounted directly above the loading coil.

160m 1.3%
80m 12%
60m 28%**
40m 43%
30m 60%**
20m 77%
** The Hi-Q site does not quote RE figures for 60/30m so I have taken an average.

Taking 160m as an example this means that for an input of 100w, 98.7w is being lost leaving 1.3w available to do the work - qrp indeed. If you're interested in qrpp just input 10w and this will produce 130mW !!

Leaving aside the ground losses, another major source of loss is in the loading coil which, in order to obtain resonance on 1.836, needs virtually the whole coil in play (maximum inductance).

The HiQ site mentions how effective the EB8 capacity hat is so I thought I'd check it out for myself.

(a) Using just the 102" whip I obtain resonance on 1.836 with a coil setting of 30 (MFJ-1924 controller) which is nearly maximum inductance.

(b) Adding a 1ft extn rod, and an EB8 with whip on top moves the coil setting to 145

(c) Adding another 1ft rod gives further improvement to 154

(d) Adding another EB8 1ft above the first together with the whip gives even further improvement to 193 on the controller.

So, all in all, there is a reduction of 163 turns in the number required to maintain resonance on 1.836 between the whip on its own and adding two EB8 capacity hats. In theory this improvement should translate into improved radiation efficiency (quoted as 1.3% for 160 using just the whip) but I'm not sure how to go about checking this.

The figure in brackets represents the % of the coil being used with each addition of capacity hat. On 160m there is a reduction of approx 50% between the whip on its own (93%) and two EB8 hats (55%).

So, adding capacity at various positions above the coil has resulted in a 50% reduction in the number of turns (inductance) required to maintain resonance on 1.836 - does this also result in a 50% increase in efficiency as well?

Top band to 30m from a small garden

This is a brief description of the antenna I use to give me coverage from 160m to 30m. Its not a pileup buster but it does allow operation on the lower bands from a 20ft square garden area.

Its a short, ground mounted, remote tuned, centre loaded vertical, based around a HiQ 5/160 mobile antenna from http://www.hiqantennas.com/ Overall height is around 16ft (4.8m) and I have added two EB8 capacity hats mounted one above to improve performance and enable continuous coverage between 160 and 30m.

The most important part of any vertical antenna system is the part you can't see - the radials. The lawn area in front of the antenna is covered with chicken wire mesh and is overlaid with 30 wire radials of various lengths. This was done a couple of years ago and is now completely invisible the grass having grown over it again.

How many radials and where to put them always seems to raise more questions than answers but I think this quote sums it up quite well,

"The biggest difference you can make is with radials. The shorter your antenna, the more important it is to have more radials. They don't need to be long, they don't need to be uniform, they just need to be there. More is better, longer is better, more is more important than longer."

The feed point is connected to a TRSB balun http://www.buddipole.com/trraswbat.html and MFJ-927 remote tuner.

Upper section of antenna showing the two EB8 capacity hats

Antenna base/feed point.

The box to the right is waterproof and contains the atu and balun.