Thursday, 2 June 2016

Having fun on the "Magic Band"

In April I installed a second-hand HB9CV for 6m, primarily for use in the UKAC VHF contests but I hoped to use it during the upcoming sporadic 'E' season.

Still a relative newcomer to the hobby (only licensed at end of 2013) I had little experience of the 50MHz/6m band and have been mostly met with static whenever I did turn the dial to have a listen but happily that has changed in the last few weeks.

I knew that 6m can be an interesting, unpredictable almost unique band.  Being at the lower end of the VHF spectrum it exhibits the usual characteristics of VHF communication, mostly short range line-of-sight contacts since 50MHz is usually well beyond the maximum usable frequency (MUF) for normal 'F-layer' ionospheric propagation utilised by the lower bands. However solar activity and other factors can trigger other types of propagation, in fact the band can support just about every form of propagation possible and is the main reason why it has become known as the "Magic Band"

One interesting form of propagation is sporadic E, or popularly referred to as Es. Small clouds of unusually ionised atmospheric gas form in the lower E-layer of the ionosphere (located at altitudes of  90 to 160 km). These clouds 'bounce' the radio waves allowing long-distance communication at VHF frequencies, sometimes multiple hops are possible giving extreme DX. One advantage of sporadic E over other forms of propagation is that it allows low-power QRP communication. As its name suggests, sporadic E is not a normal occurrence but can happen at almost any time. It does display a seasonal pattern with activity peaking in the summertime most noticeable in mid-to-late June.

I had turned the antenna to the East and have been running WSPR on and off over the last month on 6m with no luck, just the odd spot from the UK. I was in the shack one Saturday evening and was tuning around on 6m and heard some Italian stations calling CQ on SSB. I tried my luck and answered (using 50W) and was amazed to be heard, working a couple of stations in quick succession then suddenly the opening closed mid contact with another station. I was hooked!

Over the past few weeks I have caught a few more openings and have managed to work (in no particular order) Latvia, Croatia, Lithuania, Slovenia, Czech Republic, Slovakia, Serbia, Italy, Germany, Switzerland, Poland, France, Spain, Austria, Canary Islands and Finland - using a combination of voice on SSB and the JT65 digital mode.

Using JT65 has been particularly interesting since it allows me to 'remote operate' from work otherwise I would miss most of the 'Es'. Being able to monitor the waterfall and see the signals gaining and falling in strength during the minute long transmission is particularly fascinating.

Using the PSKReporter website I can see the location of all the stations I could hear and was being heard by. This map shows activity over the couple of hours on the 26 May using just JT65.

I have joined the UK Six Meter Group (UKSMG) to find out more about this "magic band" and their website is full of lots of information and resources along with the magazine Six News for subscribers.

Monday, 23 May 2016

Inverted L

I have been lacking the ability to operate on the lower HF bands, while my small 'multi-band' OCFD could be used on 40m trying to use it on 80m was nigh on impossible with my ATU. As you would expect even if matched for a useable VSWR the actual performance has been compromised.

I needed a cheap and relatively unobtrusive solution and I found one in Len Paget's (GM0ONX) design for an inverted L. The full details were printed in the Practical Wireless magazine several years ago and PDFs are available for download from Len's website. The designs make use of coaxial traps, one for the 80m version, two if you want to add a top-band (160m) option.

Opting for the smaller 80m version I set about building one. Using an old fibre-glass fishing pole about 5m high at the far end of the garden tucked behind the summer house which I could collapse down and then retract the wire elements when not in use so hiding it from view.

The fun and interesting part was building the trap. They are formed by coiling some coax, in this case RG58, round a former such as plastic waste pipe. I had a bit of scrap pipe but it was 32mm not the 40mm diameter type described in the article, thinking it couldn't make 'that much difference' I built one using the same number of turns but the resultant antenna wasn't anywhere near resonant according to the analyser.

I decided I needed to test the trap's frequency response. I found a YouTube video by Dave Tadlock (KG0ZZ) where he demonstrates using a MFJ 'Grid Dip Meter' adapter on an MFJ antenna analyser to test coaxial traps.

The adapter consists of nothing more than a coil of wire on a suitable former so I made my own to use with my AW07A analyser. It worked a treat and I discovered my trap was way off frequency. In the mean time I had located a useful PDF document by David Reynolds (G3ZPF) which informed me I actually needed 180cm of RG58 round a 32mm pipe to make a suitable 7MHz trap, so I made another.

I made a small video showing the traps and how I tested them.

The resulting antenna seems to perform well, but it does sag a little due to the weight of the trap and wire and the flimsiness of the pole. But I have made a number of contacts on it and used it during the RSGB 80m CC Datamode contest a few weeks back. It was my first go at this contest but once I got the hang of operating it was great fun.

Monday, 18 April 2016

6m/70cm antenna updates at the QTH

I have made some changes to my antenna set up. A local amateur was selling a second 13-element 70cm yagi and a 6m HB9CV antenna at a low price so decided to acquire them.

The 70cm yagi was to replace the small 7-element one which I pressed into service as a hand held antenna for potentially finding my HAB payloads last year.

To be honest I wasn't really after a 6m antenna due to the size and visual impact. I have a 6m 'wooden' moxon I made back in 2014 but it is heavy, ugly and unstable so had been collecting cobwebs in the garage. I decided with the prospect of 'Sporadic E' season around the corner I would be foolish not to put it up.

The HB9CV wasn't in the best of conditions but seemed complete albeit it was purchased dismantled. The elements were a little weathered so I set about cleaning them up with a light rubbing down with some wire wool and a rag with a drop of WD40. On closer inspection the tube that made up the front element had some noticeable bending and on removing the plastic mounting to investigate I spotted a crack in the tube wall by the hole for the mounting bolt.

While it hadn't totally separated it would only be a matter of time before it did fail as it was flexing, the plastic mount was the only thing holding it together. I found a suitable piece of alloy tube from a scrap antenna which was a perfect fit inside the broken element. I cut a suitable length and pushed it up inside the element to the appropriate position and then simply drilled through and bolted either side of the central hole to stabilise and strengthen it (can be seen in image below)

The next issue I had to address was the feed point, it came with about six inches of RG58 coax projecting from it where it had simply been cut for removal by the previous owner. I prised off the cover cap to find it full of water, the reason being a hole in the back and it being stored outside I believe.

Thankfully the trimming capacitor seemed okay, while it was wet it wasn't corroded. It was all dried out and the hole plugged with silicon and I set about re-assembling the antenna which was a little fiddly to get the phasing line to sit properly but once done it was a simple matter of adjusting the capacitor to get the VSWR to a minimum in the SSB section of the 6m band. I mounted on the rotator pole just below the X50 collinear.

I used it last month in the 6m UKAC and while my operating not exactly earth shattering I was happy with its performance using just 10W in the low power section just "search and pouncing" for a little over an hour.

The 70cm Yagi was straight forward as was already assembled, I just had to make a slight tweak to the gamma-matching bar as the VSWR was unexpectedly high around 2:1 in the SSB segment of the band, it seemed to have been tuned for the FM portion of the band. I managed just an hour "search and pouncing" in Aprils 70cm UKAC, I started late and while signal reports both ways were a marked improvement I found the extra directionality and off beam rejection something I will have to get used not helped by a temperamental rotator. 

Thursday, 25 February 2016

Some Radio Antics

Shack activity has been curtailed with the antenna 'mast' spending a lot of time luffed over due of the winter storms and high winds that have battered the UK over recent weeks.

Thankfully things calmed down and was able to put the antenna back up but I seemed a little deaf on VHF/UHF dropping several S-points on local repeaters and then started to see high VSWR readings. The incessant rain had somehow got into the connector under the collinear despite being generously wrapped in self amalgamating tape. I replaced the connector and removed a couple of feet of coax in case any had seeped into the cable.

Like much of the UK amateur community I have been trying to listen in to British Astronaut Major Tim Peake during a number of ARISS UK school contacts during the Principia mission on the International Space Station. It is pleasing to see the enthusiasm, interest and publicity it has generated for the hobby.

There is another contact tomorrow (Friday 26th February 2016 at 1440UTC) with the City of Norwich School. While reception of the first two contacts proved a little disappointing for me, the one last week was much better and I made a video during the pass.

The Astronauts are certainly busy on the space station and there was an ARISS contact this morning with an Italian school. It was a low pass here only reaching 7 degrees above the horizon but was pleased to capture Tim Kopra conversing. I was using just the X-50 collinear on the FT857-D

The repaired ATU and a new balun on the OCFD has made a big difference to HF. It is much less noisy and I am now able to match the antenna to 80m something I could never do before. While it will be very inefficient on such a short antenna I did run a little over 2W last night on WSPR as a test, and was pleasantly surprised.

I have also been doing some JT65 and for the first time some JT9 inspired by a demonstration at SKARS and I was pleased to make a JT9 QSO with JA5BDZ on 15m using 10W.

A big help to HF has been tracking down the source of my recent QRM, which wasn't as many suggested my evil PLT devices but in fact the now redundant wireless router. While the WiFi was switched off it was still being used as a network switch and for some reason had suddenly become RF noisy, it wasn't the switching PSU but the actual unit and would happen a few hours after being switched on. Funny thing it is not the first time I've had an access point suddenly emit QRM.

A couple of weeks ago I went out with Stewart (M0SDM) to assist him flying his kite antenna and we operated under the club callsign MX0SKR, for a couple of hours, it was great fun.

Last weekend I also helped my brother David (M6GTD) install a couple of antennas at the family home. He can finally use the radio he brought at the Hamfest back in September, a Diamond X-50 dual band collinear and a home brewed 33ft long OCFD should get him on the air! 

David helped me at the Hamfest with the balloon launch

My apologies if this blog post sounds like a bit like an excited child recanting his holiday "I did this, and then I did this and I also did that" I hope to post something a little more coherent and structured soon!

Wednesday, 13 January 2016

Poetic justice?

Following my last post it is perhaps ironic that for the last few evenings I have been plagued by an increase in QRM.

Trying some JT65 on 40m I was being plagued by S8-S9 of local noise, it is noise I have had regularly (even before the purchase of my PLT devices) so I reconnected up the WiMo QRM Eliminator, which has been collecting dust, to see if I could improve matters.

Using just a short piece of wire as the auxillary 'noise' antenna managed to null out most of it to greatly improve reception. No commentary on the video below but hopefully you can see it working.

Interestingly the noise seems to abate around 11pm when people are off to bed.

Friday, 1 January 2016

PLT Devices - Have I welcomed the Devil in to the shack?

I joked recently about turning to the Dark Side, well my conversion really was complete after the Boxing Day sales.

I need to set up the ability to remotely operate the station via the internet as well as experiment with internet linking systems but the wi-fi link to the shack isn't fast or reliable enough. Now if I do a scan looking for wi-fi networks I can see well over a dozen, some of them quite strong and more are popping up all the time and I suspect this congestion is part of my problem.

The Samsung Smart TV in the house was also wi-fi linked but we were having increasing issues with the BBC iPlayer and Netflix with buffering or poor quality images because of poor signal and data rates.

Ideally I would be like to fit proper ethernet cables but it is totally impractical without major upheaval or unsightly trunking a definite no-no. In the end the only workable and affordable solution seemed to be to get some of those evil Powerline Transmission (PLT) devices.

I have suffered strong sporadic QRM myself which I have assumed were neighbours PLT networking devices as I'd read the horror stories, seen the videos and anecdotal reports of mains borne noise caused by them. So I hadn't even considered it until I saw a post and video by Dan Trudgian (M0TGN) about his experiences of using some Netgear devices and the apparant lack of interference to his radio activities. Some members of South Kesteven ARS had also started using them, so I took the plunge and ordered some Netgear ones reduced on Amazon in the Boxing Day sales.

Setting them up was easy, but the acid test was how much noise did they generate? I set up one device in the shack at the far end of the mains cable run to maximise radiation. Streaming internet radio and a HD movie on Netflix I then used the FUNCube Dongle PRO+ SDR connected to the OCFD to see what noise they were generating.

Here are my observations going through the various HF bands. Where noise is present I first stopped the streaming and then powered off the devices to eliminate them as the cause, where they were the cause it seemed eliminating the network traffic was sufficient to greatly reduce the effect.

80 Meters

While the antenna isn't optimised for 80m, signals can be seen as well as noise. Before you get excited this noise has been present for quite a while and isn't being caused by the new Netgear devices. This noise is what I suspected was generated by PLT devices used by my neighbours.

60 Meters

Shocking noise but again this isn't caused by my new devices, the noise has the same characteristics as that seen on 80m.

40 Meters

The band was busy, there is some noise again but not from the new devices, this was looking encouraging. I have also showed the adjacent broadcast band.

30 Meters

Again, largely noise free

20 Meters

Still largely noise free, the QRM that is present still wasn't due to the new devices

17 Meters

This was the first indication of QRM from the new devices, however it appears effectively filtered to leave the amateur allocation clear. The faint noise in the middle picture is not from the new devices.

15 Meters

Again this band was clear of noise

12 Meters

Showing the two ends of the band again the clear signal/noise from the devices again seems effectively filtered

10 Meter

I didn't observe any additional noise on this band, but unfortunately deleted the screen grabs ;-)

So where was the QRM?

While the amateur bands appear to be filtered, the transmission can of course can clearly be seen on some non-amateur bands and apart from 16 meters seems to avoid the broadcast bands.


These Netgear XAVB5221 devices seem effective, indeed doing a speedtest in the shack was more than acceptable (the dire upload speed is a 'feature' of my cable ISP)

This fairly rudimentary testing has largely given me confidence that they won't be any issues. The band conditions weren't brilliant when I did test, but even with the absence of signals on the band any noise would be evident as seen. Yes they clearly do generate QRM but thankfully not it seems in the amateur bands. I haven't heard any extra noise on any of the radios over the last few days so all is looking promising. I will keep you posted if there is any change.

Friday, 25 December 2015

Repaired my ATU

Merry Christmas!

Not wishing to contend with an evening of dire XYL style Christmas TV (Strictly Come Dancing, Call the Midwife and Downton Abbey) I escaped into the shack and decided to repair my Vectronics VC300DLP Antenna Tuner. I got this ATU second hand last year and while it has been serviceable it had become temperamental of late. The units rotary inductor switch had become stiff and suddenly I was unable to match the OCFD on some bands so it had clearly broken.

I had a 12-position switch (rated at 5A) and knob, originally sourced for an abandoned project and hoped it would be suitable. The existing switch knob on the ATU wasn't an original, I'd assumed it had replaced one lost or broken. When I removed the cover it was clear that the whole switch had already been changed at sometime.

I also noticed a prominent burn mark inside the inductor coil, caused by a clear break in the insulation of the wire which was resting on the grounded bottom plate.

I know the previous owner of the ATU has a 300W RM BLA-350 linear amplifier, whereas I only normally operate around 30W maximum at my QTH, so not sure how much of this arcing I had caused but it needed sorting! A little over half an hour with the soldering iron and I had replaced the switch and slipped some heat shrink over the broken insulation and re-soldered the wire, lifting it off the ground plate.

The ATU seems to work well, now fitted with a new knob (just missing a cap at the moment) the switch turns nicely. I also cleaned up the SO-239 connectors on the back as they were tarnished and oxidised. I used a small bit of contact cleaner on some cotton buds to clean up the threads and the centre pins, removing a surprising amount of crud. The patch and antenna leads now screws on much better.

With the Mother--in-law staying with us over the festive period I suspect I may be in the shack quite a bit, I have plenty of jobs and half finished projects to keep me busy!