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M0SKM

Wednesday, 15 May 2019 11:47

Amateur TV through Satellite QO-100

With the launch of the Es’hail-2 satellite on November 15 2018; radio amateurs now have access to a geostationary bird.

Thanks must go to the Qatar Amateur Radio Society for the use of two transponders, one for narrowband; and the other for wideband or digital television.

Explore these links to find out more, the launch on YouTube and some technical info on Wikipedia.

This blog is an outline view of the equipment I'm currently using to transmit through the wideband transponder. I say currently as there are plans to increase the dish size and modify the power amplifier. Some of the equipment will be shown in more detail in later blogs.

My first picture is the transmitter which is based on the BATC Portsdown and incorporates a Raspberry Pi computer and a LimeSDR Mini. This particular one includes a 7 inch screen; Pi Camera and built in SMPS which supplies 5.2 volts from a 12 volt input. The Lime Mini is plugged into one of the USB ports and not seen in the transmitter picture below here.

With transmit level adjusted in the Portsdown software there is no added attenuation between transmitter and driver amplifier. In the driver amplifier enclosure which resides in the shack there are several components; I will list the key items here.
 
•    Isolator to present a load to; and protect the LimeSDR Mini.
•    Bandpass filter to reduce spurious inputs to the amplifier.
•    PTT circuit to key the amplifier from the software delayed Raspberry Pi PTT out.
•    Ex commercial class A amplifier which produces a clean 35dBm output; gain is 47dB.

Using a delayed PTT is absolutely essential as the Lime SDR goes through a calibration process at power-up; output is very big and out of band for a few seconds.

My shack is on the first floor so the output from this driver amplifier is routed to the main PA through approximately 23 feet (7m) of HDF400 cable.

Note in this next picture I have intentionally made space in the left side of the enclosure for the Lime Mini which may end up being installed here.

Same driver amp with the lid on.

Moving downstairs to the back garden I have kept the power amplifier as close to the dish as possible. Based on a repaired Spectrian board it lives in a cupboard on the patio. In a previous life the board overheated and the copper output track burnt, I wired the coax inner direct to the coupler and it works.

There's not a lot more I can say about the PA except that it probably uses more power heating the cupboard than it does generating RF power. On the heatsink I fitted a 60deg thermal switch for fan control. The Sanyo fan works extremely well but the fitted clutch makes an awful screech on start-up.

See the less than exciting picture here.

Home Sweet Home.

Several LNB's have been torn apart and tested for best results; this is the Technomate which gave an MER of 8 on the QO-100 beacon. The dish is a 1 metre Gibertini with an aluminium face. With luck this will be replaced with a 1.25 metre Gibertini.

This to me is the most frustrating element of the setup; the dual feed. Don't get me wrong I think the guys who came up with the feed done a great job on the transmit side. Credit to Mike, Paul and Remco https://uhf-satcom.com/blog/patch_antenna

For someone who is restricted on dish size and quantity receive is very disappointing; there's just so much loss. On receive the Technomate LNB produced an MER of 8dB on the beacon, using it with the dual feed it drops to 5dB. I'm currently using a Venton EXL S which performs about the same but I find it easier to mount.

If I could get away with it I'd have a second dish for receive but that's not going to happen. Perhaps some sort of Helix/LNB combination will perform better.

Anyway here's a picture of the current assembly.

73 for now.

On the first day of this event I received no signal on the first couple of passes so assumed it was delayed or cancelled. At the time I was just using my dual band vertical so not the best setup. Saturday the 9th I was tied up with other things so didn't give SSTV a second thought. Then early Sunday I saw some good SSTV pictures posted on Twitter and heard there had been a technical problem in the Russian module; all it seems was sorted now.

Keen to see what I could download I went into the shack and fired up the RX and PC; during the next four passes I got some reasonable results given my less than ideal antenna. Signals were very strong but I lost out when the ISS was directly overhead and in the antenna null point.

I've put some of the pictures in my photo gallery and you can see them here.

If you're interested in SSTV pictures sent from the ISS during previous events you can view the ARISS Gallery here.

One of my friends recently showed me an interesting YouTube video; a tutorial on receiving digital amateur TV pictures with SDRangel. All I've done is follow the instructions in the video and tested SDR devices which I own. Both RTL dongles worked fine; with the newer metal cased version suffering less drift. My LimeSDR Mini also performed faultlessly; and with the increased frequency range over the RTL devices is a better choice for me. The last test has not worked out well so far and that's using an ADALM Pluto, I understand USB performance may be an issue with this device. I'm still looking at the Pluto setup and I'll add some notes here if I can get it to work. What I'm seeing is an odd shaped constellation with the four points looking like four tear drops.

Below here are a couple of screen grabs showing results at 437MHz and symbol rate 333kS/s.

Link to the SDRangel download which has the DATV plugin included.

Link to the YouTube tutorial video. Below the video you'll find links to ffmpeg and a script which you run to add ffmpeg to your Windows path.

Hope you enjoy playing with this as much as I have. Lastly thanks to YouTuber "Corrosive" KR0SIV.

 

Friday, 04 January 2019 08:45

4 Metre DATV Upconverter

This simple to construct project uses a PCB designed by Mike (G0MJW); the circuit consists of an amplifier and mixer with filtering on the input and output. While I have used the board for 4 metres; it is possible to use the same board  for other frequencies with adjustment of component values. BATC members can purchase this PCB from the BATC shop. Circuit details can be found here.

For this project I have used one of the Chinese ADF4351 boards to produce a local oscillator at 400MHz. The 4 metre input at 71MHz is mixed up to 471MHz and the output fed to a MiniTiouner.

Another board available at the BATC shop is used for the PIC which sets up the ADF4351 output frequency and RF level. The board designed by Ron (G7DOE) will fit on top of the square Chinese ADF4351 boards. For this project I used the darker rectangular ADF4351 board so mounted the PIC Controller board on a small sub panel. You can see the board in the pictures below here. Code for the PIC is available on the BATC WIKI.

Local oscillator level for the mixer is specified as +7dBm but I found the +5dBm output from the ADF4351 board to be just perfect.

Builders have the option to use the mixer board with or without the PGA-103 MMIC amplifier, I included it on my board as I have no external antenna amplifier.

Below are some pictures taken during the build. The LED on the front panel is connected to the PIC board and illuminates on PLL lock.

 

See here the PIC Controller board top right; temporary wiring is in place to check that oscillator frequency and output levels were correct.


This picture was taken during a test prior to final assembly; note the hi-tech tinned copper wire antenna.



Now with all the plumbing and connectors in place. To the left of the PIC Controller board is a Chinese buck converter which I used to lower the input volts to a 5 volt linear regulator. This is only for the ADF4351 board as the mixer board will accept 7 to 15 volts DC.


The finished item with not so posh labels; it works a treat so I'm not too bothered about looks.

Lastly a screen grab of the output.

 

 

Friday, 23 November 2018 11:17

My Mobile Shack and Four Metre DATV

In an earlier blog my silver Ford van can be seen in a drone picture; so here's a little more detail about it.

Named Kath after my late mum the van is my mobile shack; I drive a car for trips out so the van is pretty much dedicated to amateur radio and TV. For security reasons I load the kit just before driving to the location. You'll see from the picture of the interior that some storage has been built in by one of my sons. Noticeable also is the outing was a rush job and therefore very untidy. On this particular occasion we were just granted an NOV for DATV in the four metre band so all was prepared in a hurry.

For power I use a 110 Amp leisure battery and a Honda 1000Watt generator; the battery is isolated from the vehicle electrics. During cold weather the generator can power a 600Watt heater. On the van roof bars I have added some clamps for mast support on windy days. The clamps secure a crossbar which overhangs either the offside front or nearside rear of the van. You might imagine using a van allows plenty of space for both carrying kit and operating, I found whatever size vehicle you use you'll always fill it.

Here are a few pictures.

Kath on Dunstable Downs

 

Hasty 4m setup September 2018

 

Rack and shelving in the workshop

 

 

Wednesday, 31 October 2018 21:46

ARISS SSTV Award

ARISS issue an award certificate for submission of SSTV pictures received from the International Space Station. When your pictures are uploaded to the ARISS gallery http://www.spaceflightsoftware.com/ARISS_SSTV/index.php you can claim an award by filling out a questionnaire. I'm not sure exactly what is gleaned from the data but it must give some clues to the ISS radio coverage. Here is my certificate received today for submission of the pictures in my previous blog.

To celebrate the 60th birthday of NASA the international Space Station transmitted a series of twelve pictures; of those I received ten which were fair. I'm quite pleased with them given my antenna is a fixed turnstile about eight feet above ground.

For those new to Slow Scan TV (SSTV) the pictures are converted to audio tones and transmitted over a radio link. In this case a frequency of 145.800 Megahertz. While the frequency is allocated to licenced amateur radio use; anyone with a radio scanner could receive the pictures and decode them with a mobile phone app.

Here are five received this weekend 27 to 28th October 2018. Interference on the pictures can be due to a number of issues; typically movement of the ISS or electrical noise at the receiving station.

 

Monday, 06 August 2018 16:22

BATC Portsdown driving the DATV Express

Running the DATV Express board with Windows software requires a fair amount of computer power; an i7 processor just about copes. When you get it right the output from the Express is superb;It's not a cheap board but the excellent filtering justifies the cost.

My latest project makes operation of the DATV Express much simpler and uses less processing power. The system consists of the front end and software developed for the BATC Portsdown transmitter. While the Portsdown will run as a standalone multiband transmitter it also has the capability to drive the DATV Express board. Linux based; the software in conjunction with the Raspberry Pi 3B + makes a fast and compact front end.

After taking the various components out on portable operations I decided to construct a complete package to tidy things up. Today I finalised what I will refer to as the head unit. Some tips for my build came from Noel G8GTZ who also saw the benefits of this system.

I will show some pictures and describe what I've done. The DATV Express and associated component parts (Base Unit) will be discussed and posted in a later blog.

Given the increased touch sensitivity and clarity of the 7 inch Element 14 screen I decided to use it instead of the 3.5 inch Waveshare used in my Portsdown Transmitter. Noel G8GTZ pointed out a very nice case for the screen which can be got from MODMYPI. In the picture below you can see the 12 Volt power conversion on the back. I've also drilled the case and fitted an additional audio output as the unit won't fit my shelf with a jack plug sticking out the top.

 

So there are brightness issues with some LCD screens when viewed from above and I understand the 7 inch Element 14 screen is no exception. Not sure how much truth there is in it but I'm lead to believe the manufacturer decided to invert the screen to solve the problem. Whatever you'll find the picture is upside down in this case; unless you do as I did and use a software solution to put it the "right way" up. If you use it as is; the rubber feet will be on top and you'll need to make a bracket to hold it upright. In my situation the "Head Unit" will be above my eye level so no problem having the case round the right way. More on the software fix later.

 

In the next picture you can see the contents of the box I fitted to the back cover of the case; it consists of of a Chinese made DC-DC buck converter board to allow 12Volt input. There are a couple of additional filter components and a 5 watt zener diode crowbar at 5.6Volts. The Chinese board is rated to 3 Amps but gets scary hot; there are vent holes top and bottom of the box and it has run for many hours.

 

My completed head unit will require just one cable to connect to the base unit; a good quality USB cable. At the base unit the USB cable connects to a 4-way powered USB hub. The USB cables I use are the same brand as recommended for use with the BATC MiniTiouner; Lindy Cromo.

Two software mods were made to my Portsdown installation; neither have thus far been undone by the routine Portsdown updates. The first is the fix to put the LCD up the right way; you don't need this if you're happy to use the MODMYPI case upside down. Find the fix here on Github rpi-touch-display-fix

My second software mod allows command line adjustment of the Raspberry Pi sound level; see my blog entry here.

 

As usual this item was rushed; if I missed something please ask using the home page contact menu.

73 Steve

Sunday, 29 July 2018 18:55

Raspberry Pi Low Volume

While trying to add audio output to my Portsdown DATV transmitter I found the output level from the 3.5mm jack on the Raspberry Pi was very low.

Feeling sure a web search would help I used my favourite search engine and located the solution in a post on the Raspberry Pi forum. Thanks to forum user spitecho I used a script he had posted up.

Here is the process.

Open the terminal and type the following at the prompt:

sudo nano ~/.bashrc

Now copy the following lines and paste at the end of the .bashrc file:

# Increase volume by 5%
alias volu='sudo amixer set PCM -- $[$(amixer get PCM|grep -o [0-9]*%|sed 's/%//')+5]%'
# Decrease volume by 5%
alias vold='sudo amixer set PCM -- $[$(amixer get PCM|grep -o [0-9]*%|sed 's/%//')-5]%'

Adding aliases to the bashrc file allows you to adjust the volume up or down when you login to the Pi. Having saved the editted file you should log out and back in again. At the prompt type volu to increase volume or vold to decrease.

Note: If you use this script with the BATC Portsdown it should be placed just before the following line.

source /home/pi/rpidatv/scripts/startup.sh

If you're not familiar with the nano editor used to add the two lines of code; please read up on it first.

Wednesday, 25 July 2018 16:52

Zello ATV Talkback Group - ATV East

Using the smart phone app Zello it's possible to use your phone in "Walkie Talkie" mode. This has proved to be very useful when operating portable.

In the south of england Shaun G8VPG has setup a Zello group ATV south. Since I wasn't aware of any group in the east I have created group ATV East with an uncomplicated sign in procedure. Please feel free to register if you either operate portable or wish to listen in during BATC Activity Weekends.

73 Steve

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