Posted by: GW7AAV | September 26, 2009

Some thoughts on the 5mHz Experiment

I read with interest the report by Dr Marcus Walden, G0IJZ, that he made at the IET 11th International Conference on Ionospheric Radio Systems and Techniques on NVIS propagation and the extraordinary wave mode, with analysis of 5MHz beacon data.

I have to admit a little tinge of a guilty conscience as being one of many who started out with every intention of sending log reports in to the experiment. When I received my NoV in December 2005 I even started to keep separate logbooks both on computer and on paper. However like most people I soon became disillusioned with the requested SINPO reporting. It was alien and clumsy and every one’s interpretation seemed to be different for everything other than the signal part. Even the S part of SINPO is not an accurate indication of anything as the signal strengths shown on different transceivers varied even in my own shack on the same antenna. More often than not QSB caused by NVIS and ground-wave signals arriving in and then out of phase made reporting very difficult as I sometimes would work a station that was full scale and Q5 only for them to fade to unworkable on their next transmission. Often QSB was so severe getting a SIMPO back and forth proved difficult. When the reporting station was a QRP station it could often be heard struggling. Most of use quickly reverted to the reporting system we knew and usually gave reports indicating the best signal and strength heard adding “with QSB.” I still tried to log a SINPO for a while but found that often I was still trying to work out what to write down when the next station called CQ. I guess if every one else had kept it up I would have too, but it became a chore.

My own interest being antennas and portable working I constructed a resonant dipole for the band. I started with an inverted vee and tried mounting it in various configurations and at different heights. Eventually I settled for a straight dipole strung at about thirty feet. When out portable I would use a linked dipole with links for 80/60/40/20 and 10metres in an inverted vee formation. Occasionally I would use a convenient fence post as a place to mount my antennas and very soon realised that when I did this was when I got my best crop of contacts. This led to me trying a reflector beneath my dipole at home which appeared to improve both my reception and transmitted signals. This reflector was in the form of a length of steel washing line 10% longer than the resonant dipole at around 6 feet which kept the XYL happy as she could still hang washing on it. I tried a ground-mounted reflector and found little difference to the washing line. Unfortunately I have no data that shows it worked any worse with the washing on wet or dry.

One further effect I noticed while out portable was the effect of the proximity of the ground to the ends of the dipole. Three feet seemed to be the minimum height and was usually achieved by the use of my walking poles, any lower and I would struggle to hear or be heard. This was just as true when using 2.5 watts from my FT-817 and running 60 watts or more from my FT-857.

The result of the 5mHz experiment has for me been a most interesting journey teaching me more about radio in the last four years than probably since I studied for my Radio Amateurs Exam. My own experiments coupled with a more interesting class of discussion as heard on the band have made the experience well worth the time and effort of modifying radios and building antennas. I still have not got around to trying some of the things I want to such as trying a full wave loop or making a vehicle mounted NVIS antenna. It has possibly made me a little unpopular with one or two stations due to my contention that certain antennas are not worth the wire they are made of. As I see it a quiet antenna is a deaf antenna and a poor radiator. Sometimes using a quiet antenna (none resonant) is useful for listening on as the noise to signal ratio is better. For example: I might have S7+ noise at my QTH on 60m and a station might be S8 but because of the noise he is unreadable. By listening on my 80m dipole the station shows no signal strength but is now Q5. Transmitting on my 80m dipole with a tuner in line I might just about be heard, but if I transmit on my resonant dipole I am of equal or better strength than the other station.

As a result of my experiments I realised that to carry out proper meaningful experiments a station should have both horizontal and vertical listening antennas connected to separate receivers. Now listen as a station’s signal dips on one receiver and rises on the other and the every now and then both signals shoot up when the two different phases arrive in synchrony. I probably would have never have done this and had all this fun I did without 5mHz.

As I said I have a tinge of guilt over not keeping and forwarding to the experiment the log data I should have accrued. Having had well over 2,500 QSOs on the band myself and monitoring almost 24/7 I know that the data I have seen bears little resemblance to what I have heard. Of my own total I have worked 1,479 portable stations activating for on Summits On The Air and had over 500 QSOs from 60 SOTA summits, not to mention those from beaches, holiday homes and islands. Perhaps the data from the SOTA database could be analysed because although there are no signal reports included in the SOTA records there are 27,768 chaser QSOs logged. The record of activator QSOs would be considerably higher as not all stations working an activator are registered chasers. Strangely some of the callsigns logged as being most active on 5mHz are stations I have never ever heard, while other stations that are and have been active on the band several times a day (and night) for the last four years and answer almost every CQ call are way down the list. Some well known SOTA activators appear to have been never heard by any station submitting logs, which I find incredible.

One final finding; from when I got my NoV in December 2005 for a year the band seemed to be literally bullet proof for inter UK QSOs. You could say with almost certainty when the band would come alive and when it would fade out. Then 2007 followed the pattern of 2005/6 but odd periods of a dead band began. 2008 changed with a more unreliable band and more QSB on the signals than before and sometimes the band would open and close early or late. 2008 gradually got worse to the point where instead of the band fading out at 16-17:00hrs it might be dead all day and open as we approached dusk. There seemed to be much more severe fading and long periods of no or long skip. 2009 has been the worst year so far with often 80 or 40 metres being better for inter UK and a dead band for weeks on end.

Here is to hoping we get a permanent allocation in the 60m band when the present NoVs ends in 2010. I for one still have unfinished business and I want to see what can be done on the band when we get some real DX propagation.

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