Ham on a Android Tablet

The list that follows is not exhaustive or complete, its just the most useful selection of Apps that I can fit on an old Android Tablet with limited memory. It's not my intention either to review of provide an insight into the operation of each application, that I will leave to you to discover:  after-all amateur radio is about self learning!

In my selection process I've tried to steer away from programs that duplicate each others abilities and many of them you won't find on the Google App Store. Quite a few were culled from APK file repositories and to use them you have to take on board that some may occasionally carry viruses, that's why I'm using an old machine which is dedicated to the task of portable field operation. You will need to switch off the security measures on the tablet to install them. No guarantee is given to their ability to run on your hardware either. The tablet I am using is a Huawei Media Pad Model BG2-W09, with a kernel last updated in 2018. 

Because Huawei fell from favour with Google, you will often see their products cheap in local cash exchange marts or even as scrap on social online markets, as they are no longer sent system upgrades by Google. This can work to our advantage as the newer kernels launched by Google will not run some of these apps, I guess that is why many of them have dropped from the Google App Store.   

SSTV

Robot36, SSTV Encoder, Droid SSTV, Assempix, Shredpix & Hell are image transmission and reception apps. The first four apps cover traditional analogue SSTV, while Assempix/Shredpix provide a new OFCM digital means of sending HD SSTV pictures. 

It could be said that Hell. is not strictly a picture mode however, it's a method of sending and receiving text using facsimile technology. It's unique in that the characters are not decoded, but simply "painted" on to the device screen. In transmit it uses a form of raster scan on each letter of text, effectively sending sequentially lots of tiny SSTV pictures. There's nothing new about the Hellschreiber format, it's been around since WWII, back then it used mechanical tech to send and receive the mode.

The Text on Photo app allows you to tag reports, call-sign and welcome messages to pictures before transmission. 

Text

This category of application is for sending and receiving text messages. The FLdigi application has become the radio amateurs version of the Swiss Army Knife with reference to digital communications.  Its ability to run on modest hardware in both Windows and Linux operating systems is one reason and the other its free. Packed with useful features FLdigi enables communication through a simple sound  interface, giving the operator of a amateur transceiver access to dozens of digital modes, including Morse and Hellschreiber. 

Several years back FLdigi was ported over to Android in a slimmed down format to provide a small footprint, low power messaging system, to be used in conjunction with portable HF and VHF transceivers. The idea was to provide a lightweight communications terminal on which rescue personnel in areas with zero infrastructure could provide an emergency communications network. The application was renamed AndFLmsg and provided a much simpler user interface than its big brother, while still giving access to the following digital modes:

PSK/PSKR modes, including multi-carrier modes, some of the 8PSK modes, THOR, MFSK, OLIVIA, MT-63 and Domino-Ex modes. 

The ARRL "Radiogram" message format used by the application enables the user to send both text message and photo in some of the digital modes. 

As AndFLmsg doesn't provide for Morse, RTTY and FT8 modes, the following applications have been included in my list. DroidRTTY, Morse Decoder and FT8CN, and while not a communication mode I've included WSPR tx, as its normally lumped in with and FT8 application on the PC.

Finally there is Rattlegram, a fast text system which can be used with or without a sound interface, you can just hold the Android device near the transceivers microphone and speaker and it will work. When the application  is configured correctly it will sends your call sign as a synchronising preamble, which when viewed on a waterfall display can be read as plain text. The digital modulation parameters can be adjusted in the application to enable its use on both the HF and VHF bands.

Utilities

The following applications were chosen to augment portable operation - Grid Square and What Three Words are useful when establishing your portable station. Grid Square will enable you to establish both your Maidenhead Locator and geographic coordinate, while What Three Words will help emergency services locate your position, if the area you are working from gets cut-off. 

The addition of the OS Locate application was to aid establishing your WAB (Worked All Britain) square details. Many portable and mobile stations collect WAB information to ultimately gain the award. A WAB square is a 10 km Ordinances Survey grid square. There was a custom application available to provide square ID but it's has been removed due to it no longer meeting Google's application requirements. The easiest way I have found is to use the OS Locate application, as your WAB square ID is comprised of  two letters (which reference the OS Map sheet) and the First number of the Eastings followed by the First Number of the Northings. For example if the grid reference given by the application is SU512385 then your WAB square is SU53. https://wab.intermip.net/default.php

I take the point that paper and pencil will work in the damp and they don't require power. However, Log Book can be used in their place enabling you to download a log after a contest to process the results.  An Audio Recorder application is a good feature to have on both tablet or a phone, to help captur that one prized piece of DX, or record that Morse contact you couldn't quite decode, for review later in the comfort of your shack.

AOS

When HF conditions become flat you might consider kitting yourself out with a small dual-band (2m/70cm) beam as there are a growing number of low earth orbit satellites (LEO for short), that enable both FM and SSB operation. Nothing too complicated about working through the FM birds, best viewed as a flying repeater with a huge operating footprint - see the AMSAT web pages for details:- https://www.amsat.org/. Youtube has some interesting videos explaining their operation. Anyhow,  I thought a good satellite tracking app. would be nice to have, so I've included the Ham Sat application which will provide you with  Acquisition of Signal information (AOS) - when your satellite of choice comes over your horizon and available for operation. 

Beacons  & Propagation 

Propagation information is invaluable when in the field and no one application provides the full picture, so in addition to HF Prop here are a couple of Internet links you might like to put shortcuts to on your application pages.   

https://www.ncdxf.org/beacon/index.html#Schedule The NCDXF global beacon network all share the same frequency and the application provides timing windows to show which of  the beacons is currently transmitting. In simple terms if your Morse decoding is not up to scratch you can still make a stab at what beacon you are hearing. 

https://www.spaceweatherlive.com/ Space weather is a quick and simple resource page giving magnetic, Xray and CME information

https://vhf.dxview.org/  Is a great indicator of VHF propagation both Sporadic E and Tropospheric, I think the data is collated from APRS VHF packet network data.

https://hf.dxview.org/ Is a great indicator of HF propagation showing activity on individual bands and single if required, again I think the data is collated I think from WSPR and HF packet network data.

Typical plot from the VHF DX Viewer page 

https://rsgb.org/main/technical/propagation/propagation-beacons/ The RSGB HF and VHF beacon list are a fantastic resource, and listening to beacons is a must when trying to be the first on the scene when a band opens. 

Please put a shortcut to the following:- http://kiwisdr.com/public/. Kiwi online SDR gives you access to a world wide library of online SDR receivers which enable you to monitor your own signal in other countries (am I getting out). While local UK based receivers give you the opportunity to check your audio quality and bandwidth, you see too many stations over-driving their transceivers during digital mode operation. You may find that due to age and limited resources of your tablet this application is a bit clunky, if so it can be run in your browser using the above link, I tend to use Firefox as the html sound generally works first time. 

Repeaters and Gateways

If HF conditions are a bit flat I often find myself surfing the local repeaters, and not so local, as it's surprising what a little elevation can do for your signal on VHF and UHF. That's why I've included the Repeater Book application on my tablet, the repeater lists are geographically listed with the nearest sites being at the top of the table. The app. also gives you a quick glance appraisal of each repeaters mode and access codes/tones.

I know it seems a little strange to have a DTMF code application on the list, but I often use old, or Ex-PMR equipment, that have no means of generating these tones. So in order to gain access to many of the features found on analogue gateways, I have chosen the Wolphi application as I found it the most versatile    

Lastly but no means least, I have two VOIP applications, Echolink and Peanut.  These are not really for field operation although I have used them when doing tests, they are more about staying in touch with amatures back in the UK when I'm away from home. Echolink is an old system now but it works faultlessly and has been given a new lease now VOIP software bridges have been built between the Echolink system and the AllStar network. Peanut if you like, is a new version of Echolink but spans many of the digital VOIP systems both DMR and Fusion. I've had fun too using both apps when conditions were flat, having armchair contacts with hams in all corners of the globe both day and night.  

73's

I hope you've enjoyed this whistle stop tour of amateur radio applications available for the Android OS. Tablet computers are now ubiquitous and cheap, together with mobile phones making QRP digital mode operating easy and very portable. 

If you're wondering what interface to use between the tablet and transceiver, can I please draw your attention to a previous blog:- https://www.blogger.com/blog/post/edit/5385360074172497776/5144327314764627061  There are several designs out there but all seem to be home brew.  I would say using an old tablet or phone simplifies the interfacing as these devices still rely on the good old jack plug to connect their audio to the outside world. 

I've search the halls of Ebay and found a commercial interface. I have no knowledge of it and I would suggest you read a couple of reviews before you race off  to buy one. Please see:- "EASY DIGI™ PSK INTERFACE FOR Phones/Pad's/Tablets (Apple and Android)". Unfortunately, it's made in the USA and the shipping rates are astronomic.

It may be possible to use other operating systems, but I have no personal knowledge of them, so I will leave it up to those in the know to write their own blog.

73 till next time. :)

Reference:  Please view on Youtube, the excellent videos produced  and hosted by Julian OH8STN "Off-Grid Ham Radio OH8STN". He covers the use of  AndFLmsg and the craft of hardcore portable operating.

DF Antenna & Variable Offset Attenuator

Using this 3 element Yagi along with a modern 2m receiver, signals from a FOX station can be detected up to 20 miles away in open country. As far as the receiver is concerned, an S-meter is not essential, with the aid of an adjustable attenuator, you can use the signal to noise ratio of the monitored transmission to establish the relative strength of the signal.

Building an effective adjustable attenuator at 144MHz is not easy and requires a good knowledge of screening and coupling techniques. This is where the active attenuator scores, as virtually no screening is needed; mine only uses a tin enclosure because it was available and I could solder the 50 ohm sockets directly to the chassis, providing good continuity between both.

The active attenuator presented, is really only a simple mixer, combining a relatively low frequency local oscillator, in this case generated by a clock oscillator module running at 4MHz. The level of the 4MHz local oscillator signal is easily controlled using a simple potentiometer, rather like a volume control in an audio circuit.

You may be thinking at this point, why not just use a potentiometer to attenuate the FOX signal directly? Well it doesn't really work at frequencies above HF, it's down to screening again, there is too much coupling and bypass at VHF of the variable resistor. In addition the feed impedance to the antenna will be very poor causing its directional properties to be compromised.

Mixer

The mixing in this design is performed by a single silicon diode, it takes the incoming FOX signal, for instance 144.625MHz, via the beam antenna and combines it with the 4MHz local oscillator drive. This produces mixer products and there will be two close-in images of the FOX transmission, one at 148.625MHz and the other at 140.625MHz – these are the FOX frequency plus and minus 4MHz!


If we tune the receiver to either of these mixer products they are far enough away from 144.625MHz not to swamp the receiver when close to the FOX transmitter. In addition if we reduce the level of the low frequency local oscillator, we also proportionally reduce the mixer product we are monitoring. It's a simple idea and was first aired by the ARRL back in the late 1970s, The design works remarkably well and produces a maximum attenuation range of zero to in excess of -60dB. Which with a small rubber ducky antenna will enable you to get within touching distance of the FOX transmitter, while the Yagi is used for initial cross country bearings further out.


The design shown in Figures 1 & 2 is not mine and was borrowed from Joe Moell - KØOV, there are many other derivations of the design, some using discrete low frequency crystal oscillators which are available as mail order kits.

 

Figure 1. Complete mixer circuit, the grey line around the circuit is the enclosure.

Figure 2. Internal layout of my attenuator in a small tobacco tin.

Antenna

The 3 element Yagi is constructed from a budget 5m steel measuring tape, plastic electrical conduit and fittings from Screwfix. It cost less than £15 to build, excluding some scrap coaxial cable, self-tapping screws, cable ties and Velcro patches. Again I claim no originality for the the antenna design shown in Figure 3 & 4, being sourced from Jeffrey Bail - NT1K web pages, mechanically it's been modified to work with the cheapest fittings I could get. 

Figure 3. Completed antenna with elements folded back on themselves, it can be used in this configuration when thrashing through hedges causing less element tangle.

A hair-pin match is used to balance the antenna feed to the coaxial cable, which is then coiled around the boom to form an RF choke, helping preserve the antennas directivity with reference to feeder position.

Figure 4. Hair-pin match and built in RF choke.

The antenna has a good front to back ratio and can be used back to front in order to provide more attenuation when approaching the FOX station.  Please follow the homingin.com link below, as it's a mine of useful information on fox hunting techniques. Radio fox hunting is great fun and can be done on foot, in a local park or wood,  or by car, although fuel being at a premium this is a less attractive proposition. It’s always nice to adjourn to a local hostelry when the FOX has been found, for refreshment and a wash-up meeting to compare notes. 

73 Rick G6AKG

References:

Text and artwork © 1998-2019 by Joseph D. Moell - KØOV. All Rights Reserved. http://www.homingin.com/index.html#toc

3 ELE. TAPE MEASURE YAGI, Prints By: Jeffrey Bail - NT1K. All Rights Reserved. 

https://nt1k.com/wp-content/uploads/2012/11/3L-Tape-Measure-Yagi-Assy.pdf

Linux for the Masses

So after 10 years of messing with the Linux operating system (OS) I've taken the plunge and ditched Windows. This period has seen the launch and displacement of Windows 10, with the last straw being the most recent upgrade to 11, which calls for the very latest tech to support it. I'm not in the habit of throwing out perfectly good hardware to justify the whims of a broken consumerist system, so I've pressed my ageing hardware into another stint of operation.

I've kept one really old machine which runs DOS and XP for re-programming ex-taxi radios for amateur use, which  require very slow serial port communications. The rest have been upgraded to Linux, two flavours have over the years caught my eye, both of which are serviced by the Debian Linux stable .

My daily driver is a 64bit Fujitsu Desktop with 4GB of RAM and runs Zorin Linux, I've setup the machine to look and feel like Windows 10, so as not to confuse my wife, who's knowledge of the computer doesn't run beyond using the browser and word processor.

Desktop of Zorin Linux

My hobby machine also runs Zorin Linux, the Lite version, now running on 64bit i5 Core Toshiba Laptop with 4GB of RAM, this has adequate grunt to handle my amateur radio software, including those written for Windows via Wine.

One interesting thing to note is the support for 32bit machines is disappearing fast and in order to keep a laptop running at work for browsing outside our secure system, I've opted for Sparky Linux, which again is Debian based. This has a very light footprint and runs easily with 2GB of RAM.  

Desktop of Sparky Linux

Overall I'm very pleased with Zorin Linux, I'm not a programmer and very rarely resort to running commands in text. Both flavours of Linux mentioned are written for normal folk with a modicum of intelligence. The app. store for Zorin is very shiny and easy to use and offers the biggest selection of software, the same as offered to those who use Ubuntu Linux. Support for both OS are excellent as are their user forums.  

All open source systems require external funding to keep the lights on and the bills payed. So if you find yourself switching to either above and your happy with the experience, please look to make a donation for their continued development and upkeep.  

73 Rick

Filling the void

When the Bournemouth repeater GB3SC closed down the 2m band turned into something of a local backwater. Jon G7ICH, myself and others used to hold court every morning on our daily commute via SC. To say we missed it would be an understatement, but life moves on and we let it go, because people changed jobs and their priorities change; the stuff of life!

However, with the coming of the digital revolution including Fusion and DMR, it was considered that a local DMR repeater might be a nice thing to have, particularly when connected to Brand Meister. I found a site on a high point overlooking the Poole conurbation which proved to be a good spot for our 70cm box GB7DR. The repeater deck was provided by my very generous employer and fellow ham Nick Foot G4WHO (now silent key) and the infrastructure was paid for by the Poole Amateur Radio Society. The site is provided free by Alfatronix Ltd (https://www.alfatronix.com) who keep the repeater fed and watered with a smattering of internet access. Now the bugs in the intranet firewall at the site have been sorted by Jon, the repeater gives trouble free access to DMR system - give it a go.

Analogue

I'm a self-confessed analogue amateur/engineer, and I've never liked the speech quality provided by the DMR system, plus being digital you can never have a marginal contact, when the signal gets too weak it just stops trying!
Jon, myself and several other local amateurs thought we should plough on and aim to get an analogue repeater to replace GB3SC. After asking around we managed to snag a free 2m deck in the shape of a Philips/Simoco PF10. This was kindly donated by Andrew Barret G8DOR, (past) ETCC Member for the South West. We then became doubly blessed by a chance meetings with an ex-radio amateur, turned PMR engineer Gary J. Simpson (www.commsouthern.co.uk) and ex-Southern Gas communication engineer, Mark G4SDR.

Suitable Site 

At this point we decided to look for a suitable site - having lived in the Poole/Parkstone area all my life I know the topography quite well, and the location of most of the PMR repeater sites since becoming a radio amateur in the 1980s. Several locations were selected and letters were written to site owners, only one came back as a maybe and that was from a social club in Upper Parkstone - just spitting distance from a PMR site that was about to be decommissioned. We had a couple of meetings and the senior trusty of the site, a once enthusiastic SWL, found us some attic space and a outside wall to mount the antenna, roof space proved to be warm and dry and had easy access to authorised personnel.

Lock Down

The repeater ran for nearly a year, but due to lock-down rules our friendly social club didn't ride out the economic tsunami caused by the virus. So we had to remove the repeater and start again at a new site. We got permission from Nick Foot my managing director, just weeks before his demise, to set the repeater up on a old PMR mast placed on his industrial unit by a previous tenant. The repeater was given space on a storage platform in the unit and given an AC supply and access to WIFI. The site was not as well served by the local topography, but it proved adequate after the application of an low noise receive preamplifier, which then made it accessible to most mobile stations in and around the Bournemouth and Poole area. Thanks go to Alan G7NYI for providing a brand new antenna, as the previous item had proved unreliable, and to Carlo G7IRU our group antenna rigger for fettling the feeder and mast instillation.

Something Borrowed.....

Since the first instillation of the repeater, we had been given two scrap Simoco TF2000 decks by Gary Simpson, both needed repair but after some TLC from me and help from the guys at the Simoco UK service depot both were made operational. We had by the second instillation acquired support and equipment from: - Les, G0FAJ, for the antenna and bandpass filter, Paul Marsh M0EYT, Jules Smith G0NZO and Kevin Nice G7TZC for the Heliax feeder and filter cavities. As the four cavities didn't offer the required isolation needed for the industrial location, John Fell G0API provided a circulator from the original GB3SC repeater and a low-noise pre-amp. In addition we had some financial support from the membership of the Poole Amateur Radio Society G4PRS, and a good deal of technical expertise was also provided by M0EYT, G0NZO and G0API.

A Repeater Is Borne 

We were asked by the Poole Amateur Radio Society G4PRS, if we could christen the repeater with letters to denote it was the Poole repeater, the closest we could get was GB3PB - Poole Bay. So the GB3PB repeater is borne a second time, rising from the ashes of its previous existence, providing an analogue gateway linked via Allstar to the internet. However, due to security issues it was not possible to access the repeater directly from the internet, so using RF activations and the DTMF protocol described on QRZ.com entry for GB3PB, the Allstar system can be activated. In order to offer this facility, Jon G7ICH (who is now recognised as the IT expert in the group) used a PC based application to control the repeater and a Raspberry PIE to interface with the Allstar system.

Repeater Community 

Unfortunately, COVID saw the demise of my friend and long term employer Nick Foot G4WHO. Nick was a leading light in the development of amateur repeaters locally (GB3SC & GB3SZ both silent key) but his legacy lives' on in GB7DR which he purchased, and the siting of GB3PB at his old company near Wimborne. In fact without the support of all the above persons and many I have not named, GB3PB and GB7DR would not exist. The hardware of both systems is owned by the amateurs that provided it and is a testament to the term community repeater. The best complement you could pay to the memory of Nick and co, is to use our repeater and enjoy the hobby of amateur radio and mobile operating.

Repeater Details

GB7DR occupies Channel DVU34, RX-439.425MHz, TX-430.425MHz, Colour Code 5, Slot 1 - Talk Group 9 (Local QSO), Slot 2 - Talk Group 950 (Brand Meister). Located Canford Heath, Poole. Keeper is Jon G7ICH. For complete operating details see the repeater entry on the QRZ.com web pages.


GB3PB is a 2m analogue Allstar enabled repeater serving the Poole Bay conurbation and outlying areas, AllStar node 510620. Channel RV50, TX-145.625MHz, RX-145.025MHz RX, CTCSS 71.9Hz. Located in Ferndown. Keeper Jon G7ICH. For complete operating details see the repeater entry on the QRZ.com web pages.

Last go round

The repeater GB3PB gives good coverage over the Poole and Bournemouth basin with outstanding coverage to the north of Poole, despite for the height of the antenna. It does however, have a few holes in its coverage due to the nature of the local terrain. If we could get the antenna another 5 to 10m higher, then most of the issue would disappear, but the antenna is as high as our very generous landlord would permit. :)

QRP VSWR meter that actually works.

I've been searching for a simple and cheap VSWR meter circuit that doesn't use a resistive bridge. The resistive type works well but I've found them a nuisance, as they have to be switched out of circuit when not in use as they attenuate both RX and TX signals.

Just by chance I was doing a Google image search on VSWR circuits when I came across the following from PY2OHH. This design is not easy to find on the web so I thought I would share it with you here.  In most cases I only build the reveres power side of the circuit as this is the parameter I'm normally interested in. I can assure you it works very well indeed, even with a 1mA FSD meter.  However, It does tend only runs out of puff on Top Band where it requires the full 5W to get a meter indication, all the other bands up to ten meters works fine down to 1W.

I plumped for the coiled strip-line version and used a germanium point contact diode, similar to a OA81 device to get the best sensitivity. The design is simplicity itself with no complicated coupling transformers, plus its really easy to align.

The link below takes you to an English version of the design. Miguel is experiencing some issues with his web material so I've copied his design to my Google drive.

PY20HH Design on my Google Drive

Picture from PY2OHH project notes.

30MHz and Above.

Why is there a demise in analogue amateur activity on the VHF and UHF bands, digital modes such as WSPR, FT8, Fusion and DMR are not completely to blame. The release of  digital modes, to Foundation class licenses has, in my mind, caused the problem. If a 24 month period of analogue operation on bands above 30 MHz was included, with QSL proof, became a stepping stone to the next license class it would help. Exposure to the 6m, 4m and 2m band SSB and FM would have made these operators aware of the DX possibilities of these bands, and given them a life long appreciation VHF and above. As it did me as a Class B operator under the old license scheme. I often still sit on hilltops listening for summer tropo signals to appear on hot days and for Sporadic-E openings just before a good Autumn thunderstorm. They have missed all these mystical and magical phenomenon which are a delight to me even after all these years.

Eazy Hi-Z Phones

I was looking at throwing out some scrap office telephones at work but we are not able to dump electronic waste in to our refuse. So I stripped them down to recover the plastics and was left with a pile of electronics. All good stuff , Jolly Useful Necessary Kit (JUNK) - switches, electret microphone inserts, medium impedance earpieces and other goodies like piezo sounders. Seeing the sounders took me back to an article I saw a couple of years ago where an enterprising SWL had fashioned a couple of these sounders into a pair of high impedance headphones.

Now from time to time I like to build a crystal sets just to remind myself why I got interested in radio, trouble is the only devices I have for listening on is one of those uncomfortable crystal earpieces, salvaged from an old hearing aid. So I decided to build a pair of high impedance phones using a cheap pair of ear-defenders and two of the piezo sounders.

The sounders have a very high impedance, too high for normal use, so I wired a 43k Ohm resistor in parallel with each sounder and then placed a sounder each defender ear-cup. I wired them with the cable salvaged from one of the phones in the same configuration as a stereo headset, terminated in a miniature stereo jack plug. This enables the inserts to be wired in series or parallel, in parallel the impedance of 21k Ohms is just about right for crystal set use.

Any sounder can be used, from the type you may find in musical greetings cards to the old trim-phones - bigger the sounder the better the low frequency response.

I'm very pleased with the result, my new headphones are comfortable and have a nice frequency response for communication use, together with a couple of useful resonances for peaking Morse signals - particularly good when used in conjunction with one of my simple valve regen receivers.

Selection of salvaged piezo sounders

Piezo sounders installed in cup including 

original sound deadening foam behind each insert

Finished phones including salvaged curly wire

 

 

Link to original article

https://drive.google.com/file/d/1hubS5vzhiqMuaMFrqDx2c5GLJDHal8lT/view?usp=share_link