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!

dsc_1848

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! 🙂

dsc_1850-1536x864

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

Weak signal communication, JT65 and JT9…

I promised earlier that I would do a short presentation of the JT65 and JT9 modes. Well, here it is.

 

 Light technical presentation

JT65

JT65 was created by K1JT, Joseph Taylor, a radio astronomer and also a Nobel prize winner in 1993, mainly for EME (Earth Moon Earth) communication or moon bounce at VHF frequencies and up.  Although meant for EME, it grew popular among HF operators and today it has many users on the shortwave bands. The fact that it is a weak signal mode makes it also ideal for QRP operation.

The mode itself, on air, sounds like a melody being played. A transmission is made using AFSK (Audio Frequency Shift Keying) modulation and consists of 65 different tones in which one, the lowest, is a synchronization tone. A transmission occupies approximately 177 Hz of bandwidth in the SSB passband but the actual efficient bandwidth used by a transmission is actually much smaller than that. I will return to this later on.

jt65waterfall

Fig. 1 JT65 signal in a waterfall view

Figure 1 above shows a JT65 signal viewed as a “waterfall” image. On the left the sync tone can be seen as the clear line and to the right of the sync tone the 64 data information tones are visible as white dots.

The mode is time controlled, using even and odd minutes for transmission and receiving thus showing output to the operator once a minute. This makes operation very strict and not as free as with other digital modes on HF. The actual transmission or receiving period takes 48 seconds. During these seconds a pattern of tones is transmitted which correspond to the message generated by the software. After the 48 sec the decoder at the receiving end starts processing the received tones . The processing takes a few seconds, depending of the computer used, and the output is shown to the operator as text messages. The operator then has about 10 seconds to choose an action before a new reception interval begins or a transmission starts. A typical QSO takes about seven minutes. For just monitoring the traffic a new receiving interval begins every beginning of a new minute.

waterfall1

Fig 2. A waterfall image of monitoring JT65. Notice the stations almost exact timing in starting the transmissions.

As you can see the JT mode is dependent of correct timing. The software uses the computer clock for keeping the time synchronized with an accuracy of seconds. A drift as little as two seconds makes your transmitted signal undecodable to other operators and the received signals useless. As the common home computer normally isn’t that accurate in timing the use of an NTP client software is recommended and sometimes even necessary.

In figure 2 we can see an example of a waterfall view of a number of J65 transmissions. The waterfall view is divided in to minute “rows” by red horizontal lines were each red line represents the start of a new minute. All transmissions starts after the red lines with a nearly exact timing.

As it is a weak signal mode the decoder is capable of decoding signals with a very weak signal levels. The decoder can work with signals as low as -22 dB SNR (Signal to Noise Ratio) nearly without any error and down to -24 dB with about 50% decoding error. The capability for weak signal decoding is partly made possible thanks to the use of a forward error correcting technology (FEC) called Reed Solomon. The code is commonly used in CD-ROM and Hard Drives for producing extremely low error rates in data recovery. But it isn’t only the algorithms of the decoder that makes the magic. During the 48 second transmission the message is transmitted over and over again. Up to 80% of the transmission can be lost still producing a correct decoded message. This adds to the strength of the protocol.

Other than this there is the fact that the transmitted signal Is extremely narrow in bandwidth. As I mentioned above, the JT65 mode uses 177Hz in signal bandwidth. This is the bandwidth that the transmission needs “free” for its use. In the actual transmission each tone uses only a small portion of the bandwidth almost making it as narrow as a CW transmission.

This is also a strength of this mode as it makes the use of high power unnecessary. You can work long distances with QRP equipment.

JT9

As with JT65, it was created by K1JT as development of JT65 for use on the LF/MF and HF bands. The JT9 mode are in many ways similar to JT65 as the share the same basic concept. They are both using the 48 second transmission period,  decoder and time sensitivity but there are some differences.

jt9

 Fig. 3 A JT9 signal in a waterfall image

 The bandwidth of JT9 is much narrower using only 15.6Hz of the SSB passband with a nine tone AFSK transmission. One tone is for synchronization while the eight remaining is for data.  This allows more JT9 transmissions to occupy the same bandwidth as a single JT65 transmission. The decoder is capable of decoding signals as low as -22 dB SNR nearly without any error and down to -26 dB with about 50% decoding error. This adds some 2dB compared to JT65.

Other than this the two modes is just the same to the operator and just as JT65, JT9 is perfect for QRP use.

If you want to go deeper into the protocols of JT65 the creator have made a document describing the mode more in detail. The PDF document can be found here.

73

//Anders

Antenna addition..

As I wrote in my last post I’ve started using a new exciting mode on HF, but that’s not the only thing that’s new. A friend of mine,  also a hamradio operator, was getting rid of one of his vertical antennas. As I’ve mode some experiments with a homebuilt quarterwave vertical before and was a bit curious of the construction of wideband verticals, I decided to buy it and make some tests.

The antenna is a Wimo GPM-1500 and is marketed as a wideband antenna covering 1.8 to 30MHz requiring a tuner for matching. Looks like a quite good antenna does it? Well, I as a bit doubtful that it would really be as wide banded as stated, partly from my own experience with building and measuring antennas and also from the theoretic point of view. I decided to make some measurements on the new antenna to see how wide banded it is observing the the SWR value.

For the SWR measurements I used my newly purchased antenna analyzer, the Rigexpert AA-30, measuring 0-30 MHz and a RG-58 cable for connecting to the antenna.

So I started setting up the antenna, mounting it on ground level about 50 cm of the ground on a steel pipe with no ground radials. The antenna is said to require ground radials to operate efficiently but can be operated without.DSC_0585

 

GPM-1500 @ groundlevel, no radials

The output from the AA30 showed the following values:

DSC_0588

First measurement, no radials, steelpipe mounting

As shown the SWR never dips down under 1,5. Although the SWR stays mainly about 4 and under most of the HF band. A built in tuner may be able to handle this and it seems like it may be usable on high frequencies over 30m band but on the lower bands it´s a nightmare.

I now tried to raise the antenna a few meters, because of the risk of touching the feedpoint and the antenna itself when mounted in the garden. I found a wooden pole with a length of about 2m. I mounted the antenna and it is now “free floating” without any ground connection.

DSC_0589

Second measurement, wooden pole 2m, no radials

Now the curve have become about the same as before but with a dip somewhere in the 20 m band area. Still not good in the lower bands and the higher is still around 4 with a dip in the 10 m band.  The next step is to reconnect the antenna to the ground by using a braided copper band and a 1 m copper piece driven to the ground.  This may not be a perfect ground but it is useful just to see how it affects the properties of the antenna.

DSC_0591

Antenna mounted on a wooden pole, connected to the ground with copper band.

DSC_0592

Third measurement with ground connection, no radials

This time the curve shows that the dip in the 20 m band is gone but is now widened with a value under 2 wich can be handled by a built in tuner. Lower frequencies are still bad and higher is still the same with a reduced dip in the 10 m band.

As I wanted to reduce the SWR value in the lower bands I now tried to connect a radial roughly in the 40 m band area, hoping that it may effect the curve. I also disconnected the grounding with the copper band as it had no effect on the lower bands.

DSC_0593

Copper braid disconnected and radial connected.

I decided to lay the radial on the ground as it is impractical with elevated radials with this length in my garden.

DSC_0594

Forth measurement, 40 m radial

The curves show no real improvement on the lower frequencies. More radials with the same length was connected later on but it showed no improvement as well.

I decided to stop my experiment at concluded that the antenna, as it is in my garden, is useful for 30 m band and up. Lower bands is to hard to match. I had a number of radials used for my old 20 m experimental vertical that i connected to the new antenna. They were mounted as elevated radials at roughly 45 degrees angle down to the ground. I also bought some steel tubes pushing the feedpoint of the antenna to a height of 3 m. The combination of 20 m radials and the ground connection of the steel tubing resulted in a deep dip in the 20m band with a SWR value of 1.1 and leaving the higher frequencies  between 4 and 2. The lower bands are still bad.

10644461_10152465970995838_184214448578959485_o

The final result of steel tube mounting and radial system for 20 m band.

In it´s current configuration the antenna is useful as a listening antenna for the HF bands and a transmitting antenna for 20 m band.  Even though it is useful in transmitting from 30-10 m I´m choosing to use my more efficient Inverted V antenna for transmitting. I am planning to continue with grounding and radial experiments to try to make the antenna useful in the lower bands, at least down to 40 m.

My conclusion about this antenna is that, as expected, it is a typical wide band antenna that is a compromise to make it work at as many bands as possible. The compromise is in the matching, meaning that it is more or less good matched depending on the frequency but is tunable with a riggs internal tuner. As with other verticals, the risk of RF feedback is high when the matching is not good.

In my complete station configuration it´s a good compliment, despite it´s downsides. The use of a different type of antenna located at a number of wavelengths from the main antenna makes it a good reference antenna with somewhat antenna diversity feature for incoming signals.

73

//Anders

Sharing the knowledge..

A few months ago I was contacted by the secretary of our local Ham Radio club, SK7JC, and asked if I could arrange a presentation of Digital modes on HF for the regional meeting for the Swedish national Amature radio accosiation in Karlshamn. The club had been appointed to host the meeting and was looking for activities to fill the meeting schedule.  I was thrilled and honored by the fact that they contacted me and I accepted the task and started working on a scope for the presentation.

I finally decided to have a light approach to the topic and only present the BPSK and JT modes i a light technical description, along with hardware and software demands and some useful tips and tools. To top it of, I will do a practical demonstration of a JT65/9 session to show the fun and fascination of the two modes. With this I will also demonstrate the usefulness of QRP operation with digital modes as I will use my FT-817ND  and Signalink USB interface in the demonstration.

DSC_0417

 

I’ve been working on the presentation, slides and notes a lot and I now feel like I’ve achieved a full working presentation. The Presentation will be published here on the blog the 15:th of november for those interested in seeing it. Note that It’s in Swedish! 🙂

73

//Anders

 

 

A new mode..

Well, It´s been a while since I updated this blog. It seems that time Is a rare commodity and also the fact that you have to remember to  actually update the thing once and a while. Anyway, I´ll try to make it a habit to update it more often from now on! 🙂

Since last time I´ve made a discovery of a new exciting digital mode on HF. I´ve heard it before on the bands, especially on 20m band when switching from PSK to RTTY where the activity center is located between the two subbands. What I´m talking about Is JT65 and JT9, two exciting modes for designed for weak signal communication. So far I´ve made roughly 500 logged contacts since January and worked more DX than using PSK in two years. I’ve even worked my first contact with New Zeeland, ZL3NB with a distance of 17954km, which is the furthest so far! Even some Australian stations have been worked.

So why is this mode so exciting? Other than the ease to work DX stations It´s the protocol and technology Itself that makes It interesting. I´m planing to write a longer post about the JT mode later on.

//Anders