AmateurRadio.com

The QRZ.com thread resulting from the news about the French petition to have D-Star made legal has not degenerated into the usual flame war. This afternoon it produced this interesting post by Gavin, G0LGB whe makes some observations that are quite jaw-dropping.

Gavin claims that “Repeater groups are being persuaded by financial incentives, free or drastically reduced equipment, fast-track applications via RSGB/Ofcom, to convert their under used repeaters to D-Star.” The logic of how converting an under used repeater to use a little-used digital mode will increase traffic escapes me. More likely it has to do with starting to establish a network by the back door in the hope of encouraging more users, after which the busy repeaters will come under pressure to change too. We are having D-Star forced upon us whether we want it or not!

The other worrying claim Gavin makes is that the repeater keeper has the ability to ban users, not just from the repeater but from the D-Star network as a whole. This would be fine if it was simply used to ban miscreants – though why someone would pay £500 for a radio just to swear or play music is also a mystery – but apparently people have been banned just for voicing opinions unpopular with the repeater owners (somewhat reminiscent of my own experience with the ROS digital mode!) This is possible because the system is digital – all packets of audio or data originating from you are stamped with your call so the network knows who you are and where you are (or at least which repeater you are in range of.)

I think that, regardless of the merits or otherwise of using digital voice on the VHF bands, D-Star is not the way to go. It vests too much power in the hands of one manufacturer, Icom, and in individual repeater owners. It’s just unacceptable to have a situation that could result in you being barred from your hobby just because a repeater owner disagrees with your views. I suspect that the people who find APRS too much like Big Brother won’t like this either.

I’d heard about the famous fragility of the SMA connectors used on modern hand-helds but today I got bitten by it. I was using my RigExpert antenna analyzer to check the resonance of the stock antenna supplied with the VX-8GR (which I found to be rather broad) and thought I would check the antenna supplied with the Kenwood TH-F7E for comparison. That was sharper, but the SWR was high – the best match was at 160MHz. As I was unscrewing the antenna from the SMA to BNC adapter I heard a snap. When the antenna came off I saw that the centre pin was still in the socket of the adapter. Damn!

These SMA sockets are not meant for constant swapping of antennas. The centre pin is thin and fragile, and to make things worse the pin rotates with the antenna as you screw or unscrew it, subjecting it to a twisting action that must eventually cause metal failure. All it takes is for the female to be a bit tight, if you’ll pardon the expression, and the result could be castration of the antenna.

So I’ve had it with SMA connectors. I bought two BNC to SMA adapters several months ago and the only reason I was still using the SMA antennas is that I don’t have any short BNC antennas suitable for using with the radio on my belt. But now one of those adapters will go on the VX-8GR permanently.

What’s most upsetting about this is that I’ve spoilt my TH-F7E which I was planning to sell, as the original antenna is now useless. So now I’ll have to buy a new Kenwood antenna before I can sell the radio (£24 from W&S, eek!)

Show me a tidy shack and I’ll show you the shack of someone who doesn’t spend much time tinkering with equipment, or someone who has been nagged by his XYL to make the shack tidy and curses every time he needs to connect or disconnect something – which at G4ILO seems to be several times a week.

When I switched on the computer this morning there appeared to be a Sporadic-E opening building on 2m to the south east so I switched on the IC-910H and turned the SuperMoxon in that direction. Nothing was heard, so I switched to the vertical instead and was puzzled as to why the band noise was so much greater on the beam than the Slim Jim.

The opening passed, as all such openings have this year with nothing heard or worked, and I decided to investigate. I switched the computer off and the noise fell to the same level as on the vertical. Eventually, after much trial and error and cursing because the cables can only be reached by groping blind (with the aid of a shaving mirror or a picture of the back of the rig) behind the equipment I established that the problem was the serial cable providing PTT control to the interface connecting the 910H to the computer. Even when it was disconnected from the radio, plugging it in to the serial port on the computer caused the noise level to jump up.

This was a cheap interface I’d bought some time ago for the FT-817. The serial cable supplied wasn’t screened, but I’d shortened it to use with a USB to serial adapter without a lot of spare cable lying around. This had resulted in it being too short to use with a real serial port, so I had replaced the cable. I had used screened cable for the replacement, but although I had connected the copper shield to the GND pin of the RS-232 port, it wasn’t connected to the body or shell of the plug, which in any case was plastic.

I managed to solder to the metal flange of the plug, the bit that pushes on to the socket on the PC, and connect a short wire from that to the GND pin and the shield. That seemed to do the trick, and the noise level is now the same when the beam is pointing towards the shack as it is on the vertical. Problem solved, for once! Nevertheless I do sometimes wonder if computers are worth all the trouble they cause to us radio enthusiasts.

Today I replaced the home made 2m Moxon Rectangle with a Vine Antennas SuperMoxon. As you can see from the picture of it installed in my attic it is a Moxon Rectangle with two directors that are also folded into a rectangle.

My attic, like my house, is very small. As is usual with modern British houses, the roof trusses are made of thin wood with cross-bracing for strength, so the attic area isn’t open to allow the free rotation of antennas. I have crammed rather a lot of antennas into this space to try to cover the maximum number of bands, so the VHF antennas have been forced into odd corners. Using a conventional small beam is not possible as there is insufficient space to allow rotation.

Vine Antennas claim that no other antenna gives so much gain in such a small turning circle, so it seemed like an ideal design for this situation. They claim that the directors add an extra 3dB of gain to the Moxon Rectangle design – about 9dBi which is more than a three element Yagi.

The antenna was quite expensive to buy. It is quite rugged and heavy but looks a bit home made. While the driven element and reflector made use of Jubilee clamps to tighten the main elements on to the smaller tubing used to form the corners, the directors used self tapping screws which had worked loose in transit (and probably would work loose in use due to wind vibration) and which stripped the inner hole when I tried to tighten them. You are left to your own devices to find a way to weather proof the feeder connection. Since my antenna is going to live a cosseted life away from the wind and rain I was not bothered by these issues.

The antenna presents a 50 ohm load but needs a balun to prevent feeder radiation. Vine Antennas offers a choke balun (apparently several turns of coaxial cable held in a loop using cable ties) for an extra £15. I decided to do without this, but I placed a clamp-on RFI ferrite over the cable close to the feed point which will hopefully achieve the same result.

The SWR is almost 1.0:1 at 144.0 MHz, as the plot from my AA-200 antenna analyzer shows, but it rises steeply to 1.4:1 at 144.4MHz and 2:1 at 144.8MHz. Clearly I had better not use this antenna to work satellites.

It’s a bit early to say how performance compares with my old Moxon Rectangle. The beam width does seem sharper and the front to back ratio seems quite noticeable. I heard the GB3VHF beacon for the first time since it moved to its new location, but it is in and out of the noise on slow fading as it always used to be. I can clearly hear the Northern Ireland beacon GB3NGI, which curiously is the same strength on the SuperMoxon as it is on the ribbon cable Slim Jim (which is also due for replacement with a commercial antenna.)

This antenna is probably as good as I am going to get given the restricted space available. The SuperMoxon design is copyright Vine Antennas and commercial reproduction is prohibited, which should be borne in mind if you try to make your own version.

We are entering the Sporadic-E season, the favourite time of the year for those who enjoy operating the VHF bands. As Roger G3XBM suggested today, more stations this year will be using WSPR on the 10m and 6m bands, so many openings may be detected that would otherwise be missed. I am WSPRing on 10m at the moment, and will probably move up to 6m later on once 10m starts opening on a regular basis.

However, my first love will always be 2m. From this QTH surrounded by hills Sporadic-E is the only type of propagation that allows me to work DX on that band. On 2m, Sporadic-E openings are much rarer because much smaller patches of the Sporadic-E clouds are dense enough to reflect signals at this frequency. This makes propagation between two points on 2m much more fleeting. A station can be 59+ one minute and gone the next, which makes it essential to keep QSOs short and sweet: report, locator, and name only if you are sure you have got the time.

Some people are planning to use WSPR on 2m as well, but because of the fleeting nature of propagation I am not convinced that the 2 minute periods of WSPR make it the most appropriate method of detecting propagation on this band. I think it might be more fruitful to monitor 144.8MHz which is the APRS frequency in Europe.

APRS packets take only a second or two to send, so you don’t need propagation to be good for two whole minutes to receive one. Packets do need to be received clearly, but the “strong or gone” nature of Sporadic-E on 2m suits that quite well. The main difficulty is knowing the location of the station that sent the packet you heard, since it could well be a digipeater retransmitting a packet sent from somewhere else.

There used to be a website that displayed a propagation map based on APRS packets received. But in the last few days it appears to have gone QRT, which is rather a shame. But if you are in a location that doesn’t normally hear much APRS activity, even just hearing a number of signals going “braaap” on 144.8MHz could be the alert you need that some unusual propagation is about.

If anyone has any other ideas on how to improve the detection of Sporadic-E on 2m without sitting in front of the receiver listening to band noise for hours on end I’d be interested to hear them. If you aren’t familiar with this mode of propagation and how it works and would like to learn more about it then there is an article about Sporadic-E on my website.

I heard a little bit of sporadic-E propagation on 10m this afternoon. Tuning around the beacon segment I heard the beacon DK0TEN on 28.257.5MHz quite strongly for about a minute before it faded away.

There have even been some contacts made and beacons heard on 6 metres, according to VHFDX.info. Let’s hope for some good openings on VHF this year.

It has been a glorious day today. After lunch I set off for Tallentire Hill armed with the TH-205E and three antennas: a 2m telescopic quarter wave, a 45″ 2m 5/8 wave Black Whip telescopic from eBay seller jeepbangkok and the SOTA Beams MFD.

I set up the MFD in the vertical position strapped to a fence post and put out some calls. Despite my high elevation the 2m band was quiet and I only managed to raise “the usual suspects”. Richard MM1BHO/M heard me calling through the GB3DG repeater and we had a short QSO. Then Keith G0EMM heard me call on 145.500 MHz and was willing to spend a bit of time doing some antenna tests.

Prior to this I had heard a contact on the GB3CS repeater and had quickly swapped all three antennas to see what the difference was on receive. There was no noticeable difference between the MFD and the Black Whip but both were significantly superior to the 1/4 wave telescopic (which is itself an improvement over the short whips and “duckies” normally used with 2m handhelds.) However the signal was steady on the MFD whereas it varied depending on the position in which I was holding the TH-205E with the BNC mounted antenna. When using the MFD I was sitting on the ground so it was above my head and my body wasn’t interfering with reception. When using rig-mounted antennas it is best to stand up as an extra couple of feet above ground make a noticeable improvement. But it is also worth turning around and moving a short distance as the direction you are facing can make a big difference to signal strength.

Keith confirmed that there was no difference in my signal between the MFD and the 5/8 telescopic. I was 59 on both of them, whereas I was only 4 by 3 on the quarter wave. Keith also gave me my second unsolicited complimentary report on the TH-205E audio, saying it was “just like my voice.” I was using one of the cheap Kenwood speaker mikes which I bought on eBay originally for the TH-F7E.

We were then joined by Colin 2E0XSD who again said that I was the same strength, 59+ on both the MFD and the 5/8 wave. I was only 4 by 7 on the quarter wave.

After I finished the contact with Keith and Colin I tried some more calls. I was able to access the GB3CS repeater using the MFD and the 5/8 – when in the right position – but not with the quarter wave. Some repeaters I could hear but not access even with 3W, which is what the TH-205E appears to put out on “high power” with the 7.2V battery pack, but perhaps they don’t respond to 1750Hz tone-bursts.

When I bought the Black Whip a few weeks ago I put it on the antenna analyzer and got this SWR curve. I seem to remember that I had to collapse the topmost section to get the SWR null spot on 145.000 MHz but I don’t suppose it makes any difference in practise.

I think the Black Whip 5/8 telescopic is a superb antenna for 2m FM use and well worth the few pounds it costs, as long as you have a radio that can handle it. The base is sprung to absorb any shocks but even with the HT Saver SMA to BNC adapter I was a little uncomfortable using it on the tiny TH-F7E. The big old TH-205E has no such problems with a large antenna, although its lower power output with the battery pack I have is a slight disadvantage.

Is it worth carrying the MFD instead of the 5/8, which telescopes down to the same length as a quarter wave telescopic antenna? Well, if you are using a modern hand-held radio then the MFD’s coaxial connection will avoid putting undue strain on the SMA connector. You can secure the MFD to a fence post or stuff the support mast in your rucksack allowing you to operate sitting down and even let go of the radio when receiving. The MFD is also convertible to a horizontal dipole for SSB use. So it still has several benefits. But I expect I will be taking the Black Whip on most of my hilltop outings.