80M Antenna experiments..

As the prognosis for the higher bands looks quite sad now when the eleven year cycle is heading for a low, I decided last summer to try to build an antenna for the 80M band and eventually also 160M. These bands have not been that much activated in my home QTH yet and why not get more active? 🙂

As a general rule, I prefer to have dipole antennas, mainly to keep a balance in my antenna system but with a rather small garden and the fact that a dipole for 80M is rather long I had to leave my principles and look for alternative solutions, balanced or not.

I started my experiment in July with trying to fit a full length dipole, in some way, in the backyard. Since I knew from the beginning it wouldn’t be an easy task as the whole garden itself is far from enough space to put it up in a conventional way, I started to look at alternative ways to get it up. My final solution, far from the most effective one, was to elevate the feedpoint of the dipole and leaving one leg a about 3m above ground and the other straight vertical down to ground level, using the leg more as a counterpoise. A half dipole so to speak. 🙂 The result, well I did get it to resonate but the effectiveness is probably not that good and radiation diagram should be more or less high angles. I managed to work some European stations with the antenna in the SOP-activity and after that as well. The coverage seemed to be mainly Europe and no DX-stations either heard or worked so i guessed the antenna could use more elevation.

The only way to elevate the antenna about 1/4 wavelength at my QTH is to use the house to mount the center of a full length dipole in a Inverted-V configuration. The backside is that only one leg of the antenna would be able to go the full stretch without needing a “bend”. The conclusion was to look for other alternatives.

I wanted to reduce the length of the antenna itself to make it possible to fit, both in the garden and possibly mounted on the house. I stumbled upon an antenna construction consisting of a 80m dipole made shorter with inductances which made the total length only about 17m. I decided to give it try!

The antenna is made up of four segments of FK1,5mm2 wire and two 30uH coils, spooled with the same type of wire. The antenna is feed through a 1:1 balun, which I disregarded for the time being. The segment are two 3000mm and two 5600mm wires connected as shown below. The final length of the outer wires was not consistent with the drawing as it depends on where in the 80m band you will tune it to as well on other factors.

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80m shorted dipole

The coils are made of the same wire as used for the antenna segments. For my part using 40mm diameter pipes, it took about 55 turns to achieve the correct values. The inductances was winded up on the PVC-pipes and, with the help of my Rigexpert AA30, carefully adjusted to about 30uH. I also had a small home brew center isolator with a fitted 50ohm cable which was used for the antenna. The build itself took about 8h, including the purchase of 40mm PVC-pipes on the local hardware store. To get the wires I needed I used parts of an old 3×1,5mm2 cable I have laying around looking for suitable project. After the build, it was ready to be tested.

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One of the antennas coils

I erected the antenna in a inverted-V position using my 5m fishing rod in the garden and measured the antenna. The end wires needed some extensions since the antenna was to short. A quick fix with some spare wire and the soldering iron solved the problem extending the antenna about 1m on each end. Since it is a shorted antenna, the bandwidth is no more than 20-30 kHz why it not suitable for use in the complete 80m band. I focused mainly on tuning the antenna to the lower segment of the band, aiming for 3576 kHz primarily (JT65/JT9). After some tuning in the rain and +2C (cold day) I was satisfied with the result and went in to the warm shack to do some on the air testing. After a few hours I decided to mount it more properly and moved the antenna to the back garden, removing the fishing rod. It is now mounted about 3m above ground as a conventional dipole with one end from the house and the other end in a tree, just at the edge of the garden.

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The 80m shorted dipole in the garden

When moving the antenna, the tuning made earlier of course changed why it need some more fine tuning, however the change was acceptable and I left it as it was. Further testing during the evening showed that, although mounted quite low, it still seemed to have a more favourable radiation diagram than my first experimental antenna. I actually got more heard stations outside Europe than ever before. Even a few VK-stations (VK6 and VK5) was decoded with acceptable levels. Since it’s now colder outside, I´ll leave the antenna as it is for more evaluation. Iplan to look for a mounting point on the roof of the house when the weather gets a bit warmer. 🙂

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The home brew center insulator and feeding point.

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The 80m short dipole viewed from the side with the coils to the left and right.

73 de SM7VRZ

 

 

Addition to the portable kit..

Last spring I completed my portable kit for digimodes on HF to be used during the summer of 2016. Unfortunately I didn’t got to use the kit as much as I wanted due to family activities and work, so the kit was mostly just in standby. However, I´ve promised myself to be more active this spring and summer. This because both me and the rest of the family need to get out more. That´s why I’m about to try to plan a number of outdoor activities together with the family this spring and summer and work some QSO:s with the portable kit. 🙂

Regarding the portable kit, the small Intel Atom computer I´m using for the kit is pretty slow when using it with WSJT-X 1.7. Also, the battery is not good to last more than 10 min and one hour the most on the battery bank for the radio. This made me thinking about a replacement of some kind that´s small, light and ultra portable. By accident my partner stumbled up tablet which seemed interesting.

The tablet was an Trekstor Wintron 7.0 tablet which seem to use Windows 10 Home instead of Android. This was particularly interesting as the chance that it would be able to recognize both the signalink and the CAT-adapter was quite higher than an android or Windows 10 Mobile tablet. The specs also seemed to match what I was looking for, 1.8GHz CPU and 1GB of RAM (WSJT-X requires 1.5GHz CPU as a recommendation).  The cost was only 60 Euros why I gave it a try! I ordered one online and a few days later I got the package.

dsc_1864The same night I got the package I started to experiment with the tablet. As the OS of the tablet was Windows 10 and the limited disc space of 16GB, I was afraid that it might not be able to support any of my external USB-devices. I was wrong! I also expected the Windows version to be a “sneak” version adapted for tablet use, but it turns out it really was a full Win 10 Home that was installed. It was able to handle the signalink directly to the USB port via the USB-adapter cable that came with the tablet. Since I wanted to connect more devices to the USB-port I then tried to connect a USB-hub with the signalink, CAT-adapter and a wireless mouse. This didn’t work good at first but after som tweaking in the device manager (energy saving properties) I was able to get it to work!

I then installed WSJT-X 1.7 and tried to run it monitoring the 40m band that normally has a lot of traffic during the evenings. My intention was to try to put some stress on the tablet as the decoding is the most critical point in running the JT modes. This regarding both time and processing power. It actually decode OK and the tablet could handle the extra CPU-load during the multipass decoding without any problems at all!

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Monitoring the 40m band.

No need to say I was very pleased this had worked! Now it was time to give it a trial run before officially giving it a place in the portable kit! 🙂

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The Wintron tablet with USB-hub and external devices connected.

I left it running, from fully charged, and managed to get about two hours of running time before the internal battery was depleted. An OK time! 🙂 I also made a couple of QSO:s on JT65 and JT9 and I’m more than satisfied with the solution! I also discovered that my protection case with integrated bluetooth keyboard for one of my older tablets also worked with the new one. This made the setup even more complete. 🙂

So now I have an updated portable kit, ready for this spring and summer adventures! 😀

73 de SM7VRZ

Presentation – Bockebodaträffen 2016

I detta inlägg har jag lagt upp en länk till det presentationsmateriel som jag använde under föredraget om Digitala trafiksätt på HF under Bockebodaträffen den 18/6. Jag vill tacka alla som lyssnade på min presentation och jag hoppas att jag inspirerat er till att börja titta mer på digitala moder på HF!

En PDF kopia på presentationen hittar ni här.

73 de SM7VRZ

Föredrag, Bockebodaträffen 2016

Till årets Bockebodaträff 2016 har jag blivit tillfrågad om jag har möjlighet att hålla ett föredrag om digitala trafiksätt på HF-banden. Det är med stor glädje jag har accepterat detta och arbetet med att färdigställa presentationsmaterialet samt själva föredraget är i full gång. En kort presentation om föredragets innehåll finns att ladda ner här.

Väl mött på Bockebodaträffen 2016! 🙂

73 de SM7VRZ

Sharing the knowledge, again!

A couple of weeks ago I was contacted by the project manager and president of SK7BQ, Kristianstads Radioamatörer, if I was able to host a short presentation on their annual field day/meeting called Bockebodaträffen. The meeting is a tradition since 2012 and is a get-together for local hams as well as for the hams in the southern parts of Sweden.  Usually there is a ham radio flee market but also some of the national ham radio resale companies are selling electronics and other useful stuff.

I gladly accepted the offer and since my presentation of digital modes on HF, that I did a couple of years ago, was interesting for the arrangement we agreed to do a new version of this with more focus on how to connect your radio to the computer, configuration of software’s and other good to know information. The software focus will be primary on WSJT-X and JT9/JT65 modes.

Right now I’m working with the presentation material and I do feel glad, inspired and proud that I’ll get yet another chance to share the knowledge and inspire other to start with digital modes! 🙂

Since the presentation is only made in Swedish for the moment, an English version will be posted later on for those of you who are interested.

73 de SM7VRZ

Renovation, part 2..

Yesterday, Friday, was a day of thank’s to the fact that I was on call for my work last weekend. The “free Friday” award is always a welcome thing every five week. This Friday I decided to get the KAM+ modem fixed as I previously ordered new parts to fix the faltering negative voltage in the RS-232 interface. The cost for the parts turned out to be more modest than I first anticipated as the grand totalt with shipping included landed at under 5 euros. To be honest, I didn’t strive to get the most high quality components either.  The main thing is to get the modem running again.DSC_1291

As I told in my previous post my suspicions was the electrolytic capacitors in the power supply circuits. I also believed that there might be a -5V DC voltage regulator that was broken. To start with, I decided to change the 10uF capacitors around the LT1054 circut. To be more precise C50, C49 and C48. I choosed to change all of these capacitors as they might all in time be dried up. However changing just C50 might solve the problem as this capacitor is an important part of the LT1054 circuit providing voltage output to the 7905 voltage stabilizer.

The capacitors was changed and when measuring the voltage output of the 7905 stabilizer I now got the correct voltage! 🙂 I Hooked it up to the computer and It worked! 😀 Now I am a happy owner of two working KAM+ modems! And It feels good to be able to do the repairs yourself. After all electronics is a big part of this hobby! 🙂

73 de SM7VRZ

Renovation..

The Easter weekend is always a welcome pause in my hectic work life. A lot of energy is spent on my work nowadays and It feels like I haven’t got the time for my radio hobby. During this Easter, except for spending much welcome time with the family , I also had some time doing some fault finding on my Kantronics KAM+ modem that recently decided to be non communicative. It seems like there are only garbled data coming from the device and it also seems like the processor is not recognizing  any commands you send to it. As I have done some repair on thees devices in my early working career, I had my suspicions about some supply voltages and buffer circuits in the serial interface.

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So I decided to do some fault finding on the KAM and after some searching on the internet for a schematic I found a VERY bad quality PDF copy. Since I thought that is probably the best I can get regarding schematics, I spent some time trying to interpret the strange blobs on the PDF. Rather frustrated I was close to giving up when I realized that I actually had a paper copy of the schematics in the original documentation I received when purchasing the modem a year ago. A quick search later, the paper copies was found and I started to look at the most qualified faulty components. I then got it confirmed, the serial interface is missing a negative DC voltage on the buffer circuits as well as a -5V DC-voltage. Some dried up Electrolytes and a voltage regulator having just given up seems to be the reason.

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A quick check on the preferred components suppliers web page revealed that the cost of renovating the modem would be close to 20 euros just for the components. A small price to pay. 🙂  After asking one of my HAM colleagues about borrowing an oscilloscope  for the fault finding effort, I ended upp swapping an airband-receiver for another KAM+ modem. This gave me opportunity to use the other one as a reference for a working unit.

 

So, now I have TWO(!!) KAM+ modems! 🙂 Even though I really don´t need to fix the broken modem I will do it just for fun. It also might be fun to have two working modems for future applications. 🙂

73 de SM7VRZ 🙂