International Performance

 

(Screen grab of logged contacts from GridTracker)

It's been a busy week with the radio, testing out the BBTD antenna. I really could not have expected anything like the results I've had. A quick search around the bands revealed the propagation was in and out for voice contacts, so I stuck to digital FT8. Also, at weekends I find it difficult to find casual users of the bands because they all seem to be swamped with contests. FT8 digital is designed for weak signal communications so I don't know precisely what I am achieving here. I started off making lots of contacts around continental Europe. I do have a limit on the power I can use, so even these contacts were remarkable to me. I could see markers popping up in USA, Africa, Brazil and South Asia which I thought were out of reach for me. However, one day I decided to persist with trying to contact them and it started to pay off. Finally, by the end of this week I had managed to contact USA several times, Brazil and even Japan (I really have put some hours in though!). The map above shows all the contacts I have made. You can also check them out on my contacts page in detail. Good luck with your DXing.

Terminated Dipole Update

The design and layout has changed somewhat from my original proposals. I found that I had to take up some slack with the wire lengths. I decided to change the direction through the garage to avoid close proximity with the neighbour's satellite coax cables. In total there is about 240 feet of wire in the antenna, 120 feet each leg. Re-routing the remainder around the loft perimeter sorted that out.

Ok so the antenna performed well, but I had to avoid those frequencies above about 18MHz. The SWR from 1.8MHz through to 14MHz was absolutely fine, below 2:1. It was really bugging me why I couldn't operate on the higher frequencies. So I decided to delve deeper into the problem. After much researching, I came across the KISS 16:1 balun. This was the only thing I hadn't deployed in this project. My transformer arrangement comprised of 20 turns x 5 turns of wire through the ferrites. The KISS design is much simpler employing just one coil of 4 turns, with a tap on the first turn for the 50 Ohm feed point. This is a link explaining the KISS balun. http://hflink.com/antenna/#BALUN

Because of the reduced number of turns, I could use much thicker wire (1mm sq).  Wow! Big difference. I can even tune the antenna on 50MHz. It has cost me the 1.8 MHz band but I rarely use that anyway except to listen to AM broadcasts. I couldn't resist testing on 144 and 430MHz. OMG. It works ok on these frequencies too.

Here is a quick summary of the SWR readings I got on each band:

50MHz - 1.4:1

28MHz - 2.4:1 

24.89MHz - 1.2:1

21MHz - 1.5:1

18.068MHz - 1.4:1

14MHz - 1.7:1

10.11MHz - 1.5:1

7MHz - 1.7:1

3.5MHz - 2.4:1

1.81MHz - OFF SCALE > 10:1

Let's face it. We all know that a dummy load has a perfect SWR, but it's a complete waste of time as an antenna! But overall I can recommend building this antenna as an all-rounder, or fall-back antenna. It seems to perform well, but I have nothing to compare it to really. All I know is that it is much more practical than the 1/2 wave 10m horizontal dipole in the loft, but when listening to voice transmissions, it does seem to lose the audio quality and clarity that you get with a normal dipole. Because I haven't had a voice QSO on it yet, I don't know how well it 'gets out'. The high readings on 28 and 3.5MHz could not be determined, however the on-board ATU of the IC-7300 dealt with this adequately. I feel I have accomplished what I set out to do in building a multi-band and stealthy HF antenna (and a bonus VHF/UHF too). I am getting contacts all over Europe on FT8 and 10 Watts of power on multiple bands, but as yet, not tested on SSB voice. I feel another antenna build coming on. So on to the next project.............

Broad Band Terminated Dipole

 The antenna that I started to build a few weeks ago has now been roughly strung out around the perimeter of the garden. My main aim is to be as stealthy as possible. The two lengths of wire together add up to about 132 feet. I connected it all up and plugged it into my analyser. I was really delighted with the SWR readings. from 1MHz up to about 23MHz the readings were very good - all below 2 and as low as 1.2 on the lower frequencies. Beyond this frequency, the reading starts to creep up until on 10m band it is just over 3. I am not worried about this at the moment because I intend to lengthen each leg of the antenna up the gable end to the roof and also tidy up the run in the garden, particularly away from metal objects and such. This should add about 100 feet to the total length bringing it up to a total of about 230 feet. The final SWR reading can then be determined.

FT8 and RTTY

I have been deliberating about it for weeks but I finally bit the bullet and bought an Icom IC-7300. It does everything I need and even more. I still haven't been able to get around to erecting my multi-band antenna yet because of the searing heat we are experiencing at the moment. I can operate on 10m so I set up to do some FT8 QSO's just to try the rig out. It took me a couple of days to get to grips with this rig because it does so much - there are hidden menus everywhere. Once I had set up and turned the power down to 10W, I jumped straight in with the FT8 and made 4 contacts almost immediately on 28.074MHz, 1 in Germany and 3 in Spain (see the Contacts page). Not bad for 10 Watts running on a 10m 1/2 wave horizontal wire dipole in the loft. I am using MSHV for the decoding and transmitting.

Just out of interest, I dug this info up from somewhere, I forget where from at the moment. It lists the dB signal and correlates them with the S numbers:

-26 = NOISE FLOOR
-20  = s1
-14  = s2
-8    = s3
-2    = s4
+4   = s5
+10 = s6
+16 = s7
+22 = s8
+28 = s9

 Next I turned my attentions to RTTY and Wefax. Again on the same antenna. I found a German weather transmission for RTTY on about 10.1MHz and a German Wefax station at 7.878MHz (Deutscher Wetterdienst). I used Fldigi for the decoding here. The results were a bit scratchy but as a proof of concept, it all seems to work. The poor images could be due to the incorrect antenna for the job and the fading signal.

HF Work

In preparation for getting my first HF radio, I have been looking at what I can do about an antenna. There are many different designs with just as many people saying that their choice is the best. However, my brief is restricted to space. I would love to live somewhere with a bit of land to be able to experiment unhindered, but alas, this is not the reality of the situation. Realising that the length of antenna is the key to good HF performance, I need to be able to get that into a small space. After looking at lots of designs, I settled on building a BBTD (Broadband Terminated Dipole). The diagram above shows a loft installation. If it works it will allow me to use just one antenna over a broad range of frequency bands. With this design, some amount of 'zig-zagging' the wire runs will be acceptable, allowing me to fit it into a smaller space. I have already built the terminating resistor and the impedance matching transformer ready to be deployed. It consists of a high power, non-inductive 1000 Ohm resistor and a 16:1 ratio transformer(unun).

I reckon that to get any decent performance from this I need at least 66 feet of wire on each leg. The longer the wires, the better it will perform. These lengths rule out putting it in the loft so I may run the wires around the garden perimeter somehow. The theory behind the antenna is quite simple. The terminator resistor fixes the impedance at about 1000 ohms. So to match this, the transformer has to have a ratio of about 16:1 to match the system to the feed-point impedance of 50 ohms. (16 x 50 = 800). Considering that the impedance won't be exactly 1000 ohms at radio frequencies because of inductance and capacitance, I am lead to believe that the calculations are in the ballpark.

Digital Modes

 

Although I'm not in a position to transmit my own digital data at the moment, I have been experimenting with receiving some of these modes, especially FT8 which seems to be very popular at the moment. The mainstay program for doing this seems to be WSJT-X (https://physics.princeton.edu/pulsar/k1jt/wsjtx.html). I do use this software, but I find sometimes that it just doesn't work! One day I turn it on and it jumps straight in and starts to decode. On other days, no matter what I do, it won't decode anything and I can't seem to find a reason or remedy on line for this.

 I have also been using a program called MSHV (http://lz2hv.org/mshv). So far I have found no problems with the decoding, but like I say I am unable to transmit just yet. The FT8 traffic seems to be quite heavy on 24 and 28MHz and it seems to go on all day. I do a lot of my decoding using an old Windows XP machine so I have to be picky which packages will run on it. An older version of WSJX-T will run on XP and so will MSHV.

My SDR of choice is HDSDR, a free program available for download.

My SDR dongle is the Nooelec Smart which can get down to 24MHz and goes up well above 1GHz. I love to decode data streams that are floating about on the airwaves. These include POCSAG pager transmissions, APRS packets from various sources, weather satellite transmissions, plane transponder signals (ADS-B and ACARS) and taxi MDT signals. The software for decoding all of these can be found on line for free. All good fun 😉. 

Vector Network Analyser

Because I'm always tinkering with antennas, a few months ago I saw this and decided to buy one. Probably the best thing I ever bought! The NanoVNA comes in many different flavours. The one I got was the NanoVNA-H. At the time of ordering I thought that the screen would be a bit small, but it is manageable. It measures all kinds of things, half of which I don't really understand. But for measuring impedance, SWR and insertion loss its just great. It can be used for lots more measurements when using the other channel connection like length of cable runs and fault finding etc. but I doubt I will ever use them. Like they say 'Its better to have it and not use it than not have it at all'.

If you are struggling with the screen, there's no need to worry because there is free software, NanoVNA-Saver, that solves that problem. A typical snapshot is shown above. I can now build stuff and test it there and then with this nifty little device. As with all these devices, there are a lot of fakes out there so it pays to read the vendor's feedback. I do recommend that any radio operator should have one in their toolbox.