AmateurRadio.com

This is a really cool little project.

It isn’t clear what it does from the picture, but it’s a device that makes a Morse key look to a computer like a standard USB keyboard. So you can type into your word processor, blog or whatever by sending Morse.

I want one of these. If I had to type all my blog posts using Morse I’m sure I would really get my speed up! Shame it isn’t available as a kit.

A few weeks ago I set up an experimental low power EchoLink node for use as a personal EchoLink “hot spot” using my FT-817 and a dummy load. I planned to make a a dedicated transceiver / computer interface for this. I thought I found the ideal basis for the project in this UHF Micro Transceiver Module from Elcom Research, a Greek company that makes packet radio and APRS products. The transceiver runs on 5V and can be powered by a computer USB port.

Perhaps I should have been warned off by the fact that an enquiry made through the web form on the Elcom site went unanswered, but I went ahead and ordered the module on 9th April, paying online using PayPal. After a couple of weeks nothing had been received, so I sent an email enquiry and received a reply that it had been sent by air mail and should be with me by the end of the week or the beginning of the next one. This was during the flying hiatus caused by the Icelandic volcano, so I gave it a bit longer. However it is now a week after the week that the module should have been received at the beginning of, and a further email received no answer at all. It looks unlikely that I will receive the module at all, so I guess my only option is to initiate the PayPal disputes procedure.

I spent the morning building this constant current charging circuit on to the circuit board of the junk Motorola charger I bought on eBay. I also made a power lead so that it is powered by my K2 power supply, eliminating the need for yet another wall-wart. The charger was supplied with a UK type switched mode power supply rated at 12V 1000mA. In view of the “quality” of the charger itself it is unlikely that I would want to use the wall-wart that came with it for anything, but surprisingly when I tested it I couldn’t find any obvious interference. As I have said before, the electrical noise level here is so high that something would have to be pretty bad for me to notice it, but that was a device which I expected to be pretty bad.

As I was checking the bands for new unwanted noises I heard a CW signal on the 6m band. That turned out to be EB1EHO, whom I worked for my first Sporadic-E contact of the year. I spent an hour or so on the band and worked several stations on the west coast of Spain and one in Portugal, CT1ANO.

As you can see from the DX Sherlock map, the reflective Sporadic-E cloud appeared to be located somewhere over South Wales. I did hear a Scottish station working EA6/M0DLL on the island of Menorca. The DX was right down in the noise and not copyable on my dipole but might have been workable if I had a beam. So clearly there was Sporadic-E about elsewhere.

This opening was a nice treat for a Bank Holiday and I hope is an indicator of things to come this year.

This morning I made a 6 element Yagi for 70cm using some 25A copper mains wire with the insulation stripped off and a length of wooden dowel. I copied the design from CT2GQV’s blog. The object is to see if I can hear radio signals bounced off the moon.

If you didn’t know, a bunch of guys that include Joe Taylor K1JT of WSPR fame have got permission to use the 1000-foot dish of the Arecibo Radio Telescope (shown above) for a couple of hours each day over this weekend to make radio contacts via EME. Using full power their signals should be strong enough to be heard using a hand held yagi and it should be possible to work them using just 100W with the same antenna.

I only have the FT-817 with 5W so it isn’t possible to try to work them, but I thought I would try to hear them, which is why I made the antenna. I think you’ll agree that their antenna is more impressive than mine! There are, of course, no 70cm signals to test it on, but there are plenty of noises and the yagi seems quite directional. The SWR is about 1.7:1 at 432MHz and falls gently as you go lower in frequency, but I’m not sure how to adjust it so I’ll leave it as it is for the moment.

The first session was yesterday. Unfortunately their PA blew up so they were only able to run 25W of power. Some contacts were made, but obviously not with people using low power and hand held antennas. Hopefully they will have got a PA working in time for the remaining two sessions, otherwise I am not going to hear a thing.

This evening they should be on between 1740 and 2020 UTC – that’s 1840 to 2120 BST. They will be transmitting on 432.045MHz using SSB or CW. Their call is KP4AO. The moon is only showing quite a thin crescent at the moment so it may not be easy to spot during daylight, even assuming the sky is clear as it is here. If you are in the UK the moon will be at an elevation of about 45 degrees to the south-west at the start of the session, declining to about 25 degrees due west by the end of it. If your QTH is elsewhere you can use this web site to locate it.

Tomorrow’s session is scheduled for 1840 to 2125 UTC – 1940 to 2225 BST. The moon will be in the same position relative to the start of the session.

Fingers crossed that they get the PA going so we can have a chance to hear something. If not, the antenna won’t be wasted as I’ve been meaning to have a try at satellite communications.

The TH-205E transceiver was finally restored to full working order yesterday. After some thought I finally decided how to fit the 3A diode that was somewhat larger than the recommended part which was unobtainable. I extended the left-over wires from the old fuse using thin wire taken from the leads of a small capacitor. I then shortened to a few millimetres and tinned the leads of the new diode. I wound the thin wires on to the stub leads of the diode and then soldered them whilst using tweezers as a heat sink on the thin wire to prevent the other end coming unsoldered.

The radio now works off its new battery. It made its first QSO with Derek G1GDB via the GB3LA repeater, and received complimentary reports on the audio. I even took it along to the Workington Radio Club meeting in case there was a “largest 2m hand-held” competition!

I also finished up the drop-in battery charger which I built using this circuit using an LM317T voltage regulator. It is simple to make and has an LED to show that it is charging. The hardest part was cutting the rectangular hole in the plastic project box. It’s best not to look too closely or you can see that the edges are not perfectly straight.

This picture shows an internal view of the charger. It doesn’t show the contacts for the charging tabs on the battery which were made from a paperclip. The sleeve that holds the radio or battery in position was cut from the cardboard box that my UNI-T Oscilloscope Digital Multimeter came in, and is super-glued to Veropins to hold it in place. Hopefully the heat sink for the LM317T will be adequate – the battery hasn’t lost the charge I gave it using the shack power supply so I haven’t yet had the chance to test it for a full 15 hours.

My hopes that the TH-205E I bought on eBay would be fully operational after connecting the fully-charged new battery were dashed last night when I attached the battery, switched the radio on and got … precisely nothing. However I already had a suspicion as to what was wrong. Whilst searching for information about the radio I had found information about a design fault in early models of the TH-205 that was corrected by a modification in later versions.

The original TH-205s had a miniature 4A fuse in line between the battery and the power switch. However if external power was applied using an incorrect type of DC plug, the battery was not disconnected from the supply line. The external power could overheat the battery and blow the 4A fuse. I suspected that the fuse had blown.

In fact, I’m afraid it was probably me that blew the fuse. When I first plugged in external power from my shack GSV3000 power supply I noticed the current meter quickly blip as contact was made before the power jack disconnected the battery from the circuit. I didn’t know at that time about the fault, or that the original battery was a dead short. It probably isn’t a good idea to plug in DC power leads while the power is on, but I expect I had other radios on at the time and didn’t want to turn the power off.

I opened the TH-205E up again. I could see the wires from the battery went to a jack on the RF board which is underneath the IF board, so I had to remove the IF board to get to it. This really is a nicely made radio and it is easy to take apart. The fuse, with a ferrite bead on one of the leads, was in the obvious position next to the red wire from the battery. In the picture you can see its position marked L23 after I had snipped the fuse out (I didn’t want to remove the RF board from the chassis to unsolder it completely, so I will solder the replacement to the lead ends that are left.)

I didn’t have a miniature 4A fuse to replace it with. The official Kenwood modification is to replace the fuse with a blocking diode to prevent DC power reaching the battery pack. But they use not just any old diode, but a Schottky barrier rectifier diode which has a low voltage drop of about 0.4V. (A regular silicon diode would cause a voltage drop of about 0.9V.) Of course, I didn’t have a 2A Schottky barrier rectifier diode in my parts drawer either.

I did consider simply replacing the fuse with a thin strand of wire. Since I only have the low voltage 7.2V battery pack I don’t really want any additional voltage drop. I know about the problem so I could simply avoid it by not hot-plugging external power into the power jack. But there is always the risk I might forget and I don’t want to do the repair again, so I decided to do the proper modification.

I ordered the diode from eBay supplier PIC-Projects. I have to say that eBay has become my main source of electronic components and is a major salvation when you need an odd part like this. There is no minimum order charge or handling fee that makes it uneconomic to order less than £30 worth of stuff, and the prices of both parts and postage are very reasonable. Sometimes you have to order cheaper parts in quantities of 10 or 50, just like the “professional” suppliers like Farnell, but the prices make it worth while and it helps to build up a stock of parts for future projects. I ordered 5 of these Schottky diodes because they were only 35p each, and I’m sure I’ll find a use for the other 4 eventually.

Hopefully the diodes will arrive in tomorrow’s post and I’ll finally be able to put the TH-205E on the air with its new battery!

Several months ago I had a plan to build a project using Manhattan style construction so I decided to get a tool to make myself some Manhattan pads. Constructors in the US can buy a nice hand punch from Harbor Freight for $25 – that’s less than £18. Over here the nearest equivalent cost around £90 from a tool supplier, except on eBay. I bought the eBay one, but even that cost over £30 including postage.

In the end, apart from punching a couple of test pads using the 7mm punch that was already fitted when I opened the box, I didn’t use it. Until this afternoon, when I wanted to make some smaller pads. That was when I discovered what a shoddy piece of manufacturing this eBay hole punch is.

The 7mm die was a bit stiff to remove but came out with the aid of a screwdriver in the slots provided. The 4.5mm one I put in would bind at each turn and got more and more stiff. Eventually it wouldn’t budge, so I put the screwdriver blade in sideways to get a bit of leverage. There was a crack and a whole piece of the die broke off! I guess it was made by the same firm that makes K3 knobs for Elecraft!

It’s far enough in that I can make 4.5mm pads, but not only does it not want to go in any further but it also doesn’t want to come out. I might be able to get it out with some Mole grips but this is probably the most useful size and I might never be able to get it back in again next time I need it. Crap!