SDR Web Receiver

 I am currently experimenting with putting my own SDR receiver online for others to use. This post will be updated as things progress. 

Sorry, I can't do 24x7 operation as I need my computer, radios and antennas for other things. I usually shut down around midnight (Local). 

I am currently using my RTL-SDR v4. This has HF capability but my antenna setup is currently limited so I am use a VHF/UHF Discone in my loft. Not great, but the best I can do for now. Actually, although the antenna is VHF/UHF I was surprised I can receive strong signals on HF as well, particularly the higher bands. I suspect the antenna is acting as an open circuit at these frequencies and the feeder cable is behaving as a short vertical. 

Unfortunately, my ISP won't give me a static IP address so this is liable to change. Here's how you find me. 

• Go to https://airspy.com/directory/ . 
• Search for M0BGR. 
• If I am online you will see my IP address and port (usually 5555). 
• Copy these to your favourite SDR programme and start. 
• Don't worry if my status shows 'Unreachable' - try anyway as the Airspy server is a bit flaky.

There is an SDR programme for iPhone - MagicSDR which works tolerably well. 

Here are a few frequencies you might like to try:

89 MHz to 107 MHz FM broadcast stations - lots on London, including a few pirates particularly at weekends. Above 100 MHz is mostly local stations. 96.5 MHz is my really local Maritime FM but the signal is a bit noisy here so up the gain if your programme allows this.

145.0 MHz -145.8 MHz  Amateur 2m FM. 145.5 MHz is the calling channel. 145.6875 MHz is the GB3XP repeater. 

Moving the Shack

 

Moving the ‘Shack’

My radio equipment was in my study, but when I gave up work, I moved out of that room, which reverted to being a spare bedroom. My radio equipment therefore had to move as well, which I did not relish. I have about eight antennas, all in the loft, and each one had its own feeder. These, together with a rotator cable and a couple of power cables made a flexible but very untidy arrangement. In my defence I have to say this rats’ nest was mostly hidden behind curtains but it had to go!

The Cable Arrangement in the Old 'Shack'

The easiest way to move would have been to simply transfer this cable bundle to its new location. However I wanted to take the opportunity to make the arrangement much tidier and more professional. I investigated coax switches but decided these were too expensive and introduce losses which, as a QRP operator, I could ill afford. I only use two or three antennas most of the time so I decided to build two identical patch panels, one in the loft and one at my operating position, with ‘N’ and ‘BNC’ connectors (PL-259s are banned in my shack!). 

The Downstairs Patch Panel Box  

The Design

I decided to run one RG-8 cable, for VHF/UHF and three RG-58 cables for other bands and non-critical VHF activities.

Frequency	RG-8	RG-58
Loss/100m 14 MHz	2.3 dB	5.3 dB
Loss/100m 145 MHz	6.0 dB	19.2 dB
Loss/100m 433 MHz	10.4 dB	39.5 dB

  Table - Approximate Cable Losses

 ‘N’ and BNC connectors have negligible loss at 400 MHz whereas the loss of PL-259 connectors rises rapidly above about 200 MHz  My longest cable run was less than 10m, from equipment to antenna, so the RG-58 cable losses are acceptable at VHF except for contests etc. when the RG-8 comes into play.

The Installation

Installing the cables was very straight forward as I planned an almost vertical drop from the loft junction box to the operating position. I measured the cable lengths then added a bit. I terminated the four cables in the loft patch panel before installing it. I then screwed this to a handy loft timber and carefully drilled a hole in the ceiling plasterboard directly above the operating position. I then fed the four coax cables and the rotator cable down to the operating position and enclosed them in plastic trunking. I trimmed the cables to length before terminating them in the downstairs patch panel and screwing this to the wall.

I decided not to fit connectors to the rotator cable as this already has a screw terminal on the control unit and the rotator assembly. I did not trim this cable so I will have flexibility if it needs to be moved. The surplus cable is coiled in the loft.

I then made up a set of patch cables (RG-8 or RG-58) to go from the upstairs patch panel to the antennas. There is less than 1m from the downstairs patch panel to the operating position and I already had several 1m BNC-BNC cables so no work was needed here. Incidentally I like BNC connectors because of they connect quickly and securely. As I only run QRP, their power handling is not an issue as it might be at higher powers. 

The New 'Shack' Operating Position

Operating

The downstairs patch panel is very convenient when I need to change antennas as I leave the most commonly-used ones connected up top. I do have to climb up when I need to change the ones in the loft but this is not a massive inconvenience as I have a sturdy loft ladder. I do need to remember to write down the upstairs configuration and pin this on my notice board whenever I change anything up there; my memory is not what it was!

As a result of this move, my entire station including a small storage unit for hand-helds, cables , microphones SDR radios etc. now occupies less than ½ sq m, which has pleased the XYL, and I have not lost any operating capability. The cables arrangement is now much more professional looking and I am pleased I have achieved all the design objectives.

  

Is FT-8 Mode on Amateur Radio the Way Forward?

 

It is easy to see why FT-8 has become such a popular mode on the amateur radio bands, especially in these times of poor HF propagation and high man-made noise levels in urban locations. I have used FT-8 myself and worked 16 countries in an evening with low power and indoor antennas. This would have been a challenge using SSB, CW or PSK-31 but it was really easy on FT-8.

This did not take any great skill on my part. I tuned the radio, connected it to my computer via my Signalink sound card, started the WJST programme and waited a few seconds for calls to appear. A station was calling ‘CQ’ so I clicked on his call sign and the computer did the rest.

I question whether a FT-8 exchange really is a ‘valid’ QSO.  So let us examine a typical ‘QSO’ in detail. Exchanges on FT-8 are limited to 13 characters:

·         I see a ‘CQ’ call on the WSJT ‘Band Activity’ window from HA7xx. This tells me the station’s call sign and 4-charater Maidenhead grid (JN97). I click on his call and my computer automatically send a reply with my 4-charater Maidenhead locator (JO01).

·         He replies and sends me a signal-to-noise report (SNR). I automatically reply to this with his SNR report.

·         He acknowledges and the QSO ends, automatically. All that is left for me to do is to click ‘OK’ to conform the log entry that WJST has generated, automatically.

The information we have exchanges is:

• ·         Call signs
• ·         4-Charater maidenhead locator
• ·         Signal-to-nose ratios.

From this QSO, I know nothing about the other guy, name, where he is, type of equipment etc.  The 4-charater locator puts him (I don’t know if it’s him or her, but I will guess for the purposes of this post) somewhere in north-central Hungary. I only know he is in Hungary because I am familiar with the ‘HA’ prefix. Without this inference he could also be in southern Slovakia. FT8 does include a 'Free text' field of 13 characters so it is possible to send additional information during an exchange but I have seldom seen this feature used on the air. 

Surely, the Signal-to-Noise ratio is useful information as it is a very important property of any communications link? Actually it tells me very little about how my equipment is performing. For example, if a station tells me my SNR is +10db I know we have a good link and my equipment is performing OK. However, if a noise source, local to him, starts and raises his noise floor by 20db my SNR will degrade to -10db even though nothing at my end has changed.

SNR is only useful if it is used to manage a communications link, for example I could adjust my power, or bit rate to optimise use of the link. Unfortunately in standard FT-8 QSOs, SNR is sent right at the end of the QSO, just before ‘73’, so there is no opportunity, or reason, to adjust my equipment settings to optimise use of the link.

One thing that I am concerned about with FT-8 QSOs is: what would I say to a curious friend to whom I was demonstrating Amateur Radio? The friend might ask, where in Hungary is he? What’s his name? Etc.  and I would be unable to answer these or other reasonable questions, about the station I have just ‘worked’, and from this my friend might conclude that amateur radio is a waste of time.

It can be argued that FT-8, because of its increased sensitivity, identifies propagation modes that otherwise would not be seen (see Radcom March 2021). My QSO, which was automatically uploaded to 'PSKReporter', might provide a data point for academic research into propagation, but I doubt if anyone would be surprised that there is a path on 40m between UK and Hungary on a summer's evening.

I am not resistant to change in Amateur Radio, which must innovate to survive. I enjoy many older modes, particularly is they require a degree of skill, such as CW, PSK-31 etc, but I also enjoy innovative digi-modes, though not FT-8, as you will have gathered by now. I am not opposed to automatic quick-fire QSOs in appropriate circumstances. They have a place when transmission paths are short-lived or highly unstable, examples are EME or meteor scatter, but I see no useful place for these modes in main-stream HF communications.

I particularly like JS-8 mode. This uses a similar coding scheme to FT-8 and has some automatic click-and-work features. However it is not tied to FT-8’s 13-charater exchanges and so can do more; much more:

• ·         Unlimited QSO length so you can simply exchange reports or have a long chat
• ·         Work stations via intermediate stations (Relay)
• ·         Send, store and forward messages.
• ·         Adjust bit rate, transmit power etc. so you can actually make use of SNR information.
• ·         Beacon mode so you can see propagation changes in near real time.

Prior to FT-8, I was concerned about the move towards ‘Rubber Stamp’ QSOs, where we simply exchange fictitious ‘59’ signal reports and move on to the next QSO, started amateur radio down the road of irrelevance and FT-8 continues on that path. I would not go as far as to say it should be banned, but regular users might think about using other modes that permit substantive QSOs, require a higher skill level and are useful for exchanging real information such as could be used for emergency communications should the need ever arise.

As always, comments are more than welcome.    

NanoVNA V2 Vector Network Analyser

 

Nano VNA

I recently bought a Vector Network Analyser. These instruments used to cost hundreds of pounds, but the Nano VNA V2 sells for around £60.

What does it do? It is used to characterize the impedance of antennas, cables, connectors etc. It can measure SWR, Impedance, insertion loss, return loss and much more. Its range is 50 kHz to 3 GHz, but the measurement range is programmable so, for example, you can just scan the width of an amateur radio band. It also has a time-domain reflectometry function allowing length of coax cables and identifying faulty connectors in a cable run.

The unit I bought has a 7cm screen. This is small and the screen is a bit hard to read but it does make the unit very portable - it fits in my pocket. A larger size model is available. The screen is touch sensitive and a stylus is provided which makes using the menus easier. If you find the screen too small, PC software is available but of course this limits portability – one of the major advantages of the NanoVNA.

    

                            NanoVNA and Accessories

Accessories:

• ·         Stylus
• ·         Two SMA-SMA Cables
• ·         SMA Socket-Socket.
• ·         50 ohm calibration load
• ·         Short circuit calibration load
• ·         Open circuit calibration load
• ·         Carrying case (but the zip on mine soon broke)

Be careful not to lose these accessories! It has a built-in rechargeable battery that is charged via the USB socket. The connectors are SMA - these are not PL-259s and need to be treated with care. 

Using the NanoVNA is straightforward, but do read the online instructions. When it is switched on four traces appear. I usually switch three of these off to simplify the display. The frequency range over which you want to measure is then selected and the next job is to do a calibration for the frequency range. This takes a couple of minutes by connecting the Open Circuit first, then the Short Circuit and finally the Dummy Load. There are five memories that can store frequency range/calibration. If you want to change the frequency range, and you have not previously stored it, then you need to do another calibration and store that.  

I found the NanoVNA easy to use. For years, I have used SWR meters to check the performance of my antennas etc. but these only tell part of the story and manually plotting SWR curves is tedious. With the NanoVNA you can see the selected frequency range on the screen and quickly switch to other functions, such as real and imaginary impedance. If you want to use the more advanced functions then read the many online tutorials, such as The Antenna Theory Website (antenna-theory.com). If not connected to a PC then the quickest way to record results is to take a photo of the screen. I found time-domain reflectometry function a little tricky but everything else is straightforward.  

        4m Whip Antenna VSWR

 

 

 

 

Tytera MD-UV380 2m/70cm Radio for FM & DMR

I already owned a TYT MD-380, 70cm analogue and DMR radio but I recently bought a MD-UV380 which does both 2m and 70cm analogue and DMR. It also has other improvements.

The MD-UV380 is well built and robust. It looks very similar to its predecessor. Differences include:

• Covers 2m and 70cm.
• Zones and Scan Groups can have up to 64 channels.
• You CANNOT use Toolz, software that added functionality to older TYT radios.
• You need different software, from TYT site, to edit, upload code plugs etc.
• I have not figured out how to upload the world-wide Contacts database but individual contacts can be added as required.
• Zone members can be added from radio.

Other code plug editors, such as the one by G6AMU are easier to use but the current version will not talk to MD UV380, so edit in G6AMU save and upload with Tytera software - a bit of a pain but not difficult. 

A word to the wise! Save a backup copy of your existing code plug BEFORE you edit it so if you get in a muddle you can revert to a known, working version!

When you get your 380 it’s just a paperweight until you load a code plug to define channels etc. You can write this yourself or ask online or at your radio club for a ready made version suitable for your area. A major drawback of this radio is the very poor user manual and no ‘Help’ file with the TYT software (or the G6AMU editor). So, although I like this radio it is not great for anyone unfamiliar with DMR, unless you have a mentor to help you. 

On the air, the radio works well and, once I had figured out how it works, it is fairly easy to use. The display is clear except in very bright light. Audio reports of my transmissions were good and received audio clear. Battery life is good and don’t forget DMR transmissions are more economical than FM as the duty cycle is 50%.

In summary, this is a great radio and currently sells at a good price. Its documentation and software help files need to be greatly improved. 

R820T2 SDR Radio Receiver

 R820T2 SDR Radio Receiver

My current direction of travel, with amateur radio and other
things in my life, is to downsize so I can continue with my radio hobby in
smaller accommodation when the time comes. I am therefore a convert to Software Defined Radios
(SDR). These are tiny radio receivers, typically the size of a memory-stick
dongle, and controlled by software on a computer. This means the equipment size
is minimal and the cost/performance ratio of an SDR radio can be very high.

I recently bought a R820T2 SDR from Nooelec on Amazon. I had
previously owned a R820 SDR (see earlier post) but the performance was very disappointing
and I recycled it. I needed another receiver because I wanted to monitor marine
AIS signals without tying up one of my other SDRs or my main transceiver. I had
heard that the performance of the R820T2 was much better than previous R820
radios and at less than £25 I decided to give it a go

The package arrived and contained, as advertised, the
R820T2, a small (300mm) telescopic whip antenna. Before using the R820T2 as a
radio receiver, rather than as a Digital TV, it is necessary to change the
Windows driver using a little utility called ZADIG. This is very
straightforward and there are plenty of instructions on line how to do this so
I won’t repeat them here. Do not
load any TV software that might come with the SDR and of course set a ‘Restore’
point before changing drivers so you can back out in the unlikely event of
something going wrong.

That done, plug the SDR into a USB port on your computer and
plug your antenna into the MCX female connector on the SDR. If you do not want
to use the supplied whip antenna adapters from MCX to SMA, BNC etc. are
available from electronics suppliers and these make it easy to connect other antennas.

Next, start your SDR software. I use SDR Console and SDR#
(SDR Sharp) which are free downloads. Select RTL Dongle or RTL USB from the ‘radio’
menu, set the frequency you want and the mode and then ‘Start’ and you should
be in business.

So what does the R820T2 + software do?

• ·        
  It tunes from about 25 MHz to around 1.8GHz so
  it covers the VHF and UHF amateur radio and commercial bands
• ·        
  It also does the 10m amateur band with limited
  performance.
• ·        
  It does not care what mode you want to receive –
  SSB, AM, CW, FM, Digital etc. as this is taken care of in software on your computer.
• ·        
  In addition to amateur radio, you can receive
  broadcast station, marine voice and AIS signals, aircraft voice and ADSB
  broadcasts and much more provided this is legal where you live.
• ·        
  You can receive signals from amateur radio,
  weather and some scientific satellites, including ISS.

I will say more about AIS, satellites and ADSB other posts.   

I found the 820T2 performs very well and not much worse than
the more expensive SDRs that I own. Filtering is much better than with earlier versions of the R820 SDRs. Certainly works well enough for a beginner to
enjoy or as a secondary receiver for a licenced amateur radio operator.  I use it as a second receiver when operating
VHF and UHF contests as I can see station pop up on the software waterfall
display. Although the whip antenna is small, I found it actually works
surprisingly well if it is located in a good position (high up by a window for example), but obviously ‘real’
antennas will give better performance.  

In summary the R820T2 and one of the software programmes make a very credible VHF/UHF all-mode
receiver and a fraction the cost of ‘real’ radios. It takes up almost no space
so is ideal if you live in restricted accommodation. Its performance is vastly
better than previous R820 receivers and would make a great Christmas or birthday present
for anyone interested in radio or thinking of starting out in the hobby.

Please share your experiences with R820 SDR Radios by commenting here. 

SignaLink USB Digi-mode Interface

Digi-modes are attractive to me as they enable long-distance contacts with my low power and limited antennas. There are numerous computer programmes for the different modes and many multi-mode programmes. They all have one thing in common, it is necessary to make multiple connections from your computer to your radio

.

• Audio out of the computer,
•  Audio into your computer,
• ‘Press to talk’ to control when the radio listens or transmits.

This would require several cables and level settings to get satisfactory operation. To make matters worse, my old computer gave up the ghost and my new computer has no microphone socket, so I have to use an external sound card – more wires and more things to configure.

I use my computer for many things, not just amateur radio, so I cannot leave the amateur setup permanently configured. This meant the setup time was too long and too error prone for a quick go on digmodes. Then, my life changed! I came across the ‘SignaLink USB’ interface unit which has its own internal sound card and only requires two cables. (plus a couple of optional connections that I don’t use).

      

                  

Signalink Front and Back

First thing to say is that it’s small 80w X 100d X 40h (mm, in case you are wondering) which is entirely consistent with my station design philosophy. It only requires two cables:

• ·         From the unit to a computer USB port (supplied with the unit)
• ·         From the unit to your radio. These are bespoke cables that you buy when you order the unit if you do not want to make your own.

The SignaLink USB comes with comprehensive instructions and more help is available on the www.tigertronics.com web site if you need it. Documentation is good.

Setup is very easy. Internal adjustments are necessary to match the SignLink unit to your radio. This requires the unit to be opened by removing the four Allen bolts on the front of the unit and sliding the innards out. There are two ways to configure the unit:

• ·         Use the supplied jumper wires using the diagrams available on the supplied CD or from the www.tigertronics.com web site. This is the best option if you will want  to change radios often.
• ·         Fit a ‘plug and play’ jumper module for your radio that can be bought as an extra. This is the best option if you only want to use the SignaLink with one radio.

The process is very straight forward, but do read the instructions before you start.

This brings me to the only criticism I have – the Allen bolts are not metric size. If you are in Europe, this is a real pain because the old Imperial size Allen Keys (Wrench) are very hard to find here. One is supplied so don’t lose it! In my professional life, I would never buy equipment that used non-metric bolts etc. for use outside USA.  This would cause maintenance issues because the imperial tools, which were usually supplied, would invariably get lost or stolen.

Signalink Inside

Once the internal unit is back in the case and the Allen bolts fitted you can begin setup. This is very clearly described in the supplied documentation. This does involve messing around with the Windows sound controls, to set up the SignaLink internal sound card, but once this is done you seldom need to go there again. This is because the SignaLink has analogue volume control knobs on the front for transmit and receive so adjusting levels while operating is very easy.  

That’s it, you are almost ready to go. I leave the SignaLink connected to my radio so all I have to do is connect the SignaLink to my computer and switch it on. The SignaLink is powered from the USB port so no need for an external sound card or power supply.

Start your digi programme and select “USB Audio Codec” for the input and output. Check the receive signal level and adjust the RX control on the front of the SignaLink. Send a tune signal and adjust the TX control on the front of the SignaLink for the correct level (then back it off a fraction of a turn!).

I have tested the Signalink with the following software:

• ·         MultiPSK – the Swiss Army knife of digimodes.
• ·         WSJT (FT-8, WSPR etc.).
• ·         SeaTTY – for receiving weather reports etc.
• ·         WinWabler.

It works fine with these applications, and I don’t doubt, with many others as well. It is now very easy to get on the air and so I am able to do digital sessions even when time is limited.

As the Signalink unit is small and simple to set up, portable digital operation such as a SOTA expedition, with a tablet for example, is quite feasible. Unfortunately, at the time of writing, UK is in lockdown for the CV-19 pandemic so I have not tried this yet.