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  • filter_header.jpg
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M0SKM

Sunday, 01 January 2017 00:41

Ardupilot Mega On Screen Display

This simple On Screen Display uses a board intended for use with a drone or quadcopter. The project was devised by Mike Stevens G7GTN and published in issue 12 of CQ-DATV.

Video quality from the finished item is excellent and ideal for use with amateur TV output. You should understand output is monochrome and single page.

Two PCB's are used in the project but only one is permanently installed, the other is used for programming. Unfortunately there are no mounting points on the OSD board so a little fabrication is required if you plan to box it up. I soldered some push pins to the grounds on mine and soldered the other end of the pins to copper clad board. If you want to run from the shack 13.6v supply a tiny regulator board can be added. See picture.

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Out of the packing the OSD board is pre-loaded with a font set suitable for aircraft use e.g. an artificial horizon, not useful for amateur TV. Mike has provided a font set which can be downloaded and installed using the Arduino IDE software and a simple to use terminal programme. All instructions and software links are available on the CQ-DATV site so I will just outline my build.

Before you connect up the board there is a small amount of soldering needed. The OSD board has two isolated sections. At one end video output at 12v and at the other digital input at 5v, the 12v input feeds a 5v regulator which we are told is prone to overheating. For this project the two sections are linked and run with a single 5v supply. There are link points on the board so the alterations are a five minute job with the right tools.

Digital input to the board is serial so the second board you'll need to source is an FTDI USB to Serial interface. These are cheap as chips from eBay; mine was less then £3.00 delivered. Most will come with a set of leads. Beware as some Chinese sellers advertise as FTDI and supply an alternative which in my case didn't work.

Pictured is the genuine board which is only required during programming. Mine can be re-attached if I want to make changes.

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Prior to boxing up; the parts cost less than £10 and it worked great. I built two of these with different talkback frequencies; a paged unit is planned using several boards in one enclosure.

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OSD with no video input. Monitor TV is under a shelf causing some shading at the top.

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Links. Working at time of writing. There are other suppliers for the hardware.

CQ-DATV issue 12.

On-Screen Ardupilot Mega Display MinimOSD Rev. 1.1

FT232RL 3.3V 5.5V FTDI USB to TTL Serial Adapter

Monday, 06 June 2016 17:11

2 Metre Bandpass Filter

This 2 metre BPF was a design I found in the Radio Communications Handbook page 5.30. Having recently committed my existing filter to a breadboard project I decided to go ahead and construct a replacement.All of the critical dimensions are shown in the handbook so construction was quite easy.

Since I completed the filter it has been aligned by a friend Arthur G4CPE. Setup was carried out on Arthur's Wiltron RF Analyser. Bandwidth is 5MHz and loss is under 2dB at 146.5MHz.

This is an inexpensive project using basic tools, coils are wound on a 9.5mm drill bit and the piston capacitors were found on eBay. There's not much to it as you can see from the pictures below.

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Wednesday, 18 February 2015 22:24

Power Amplifier for 2 Metres - Continued

Well the Res Ingenium THV15 VHF pallet amplifier arrived from the Netherlands as expected. I quickly unpacked it to check it was all okay, it had been described as brand new old stock. Sure enough the amplifier was in the original packing and sealed in an anti-static bag....great.

What was needed now was a few hours work to make it usable.

Following a visit to Arthur G4CPE I left with some useful tips and a gift of a chunk of heat sink; off I went to make the pallet a home. I should mention that the heat sink and its base compartment was over a foot long, time to fit a new blade to the hacksaw and locate the tin snips. An entire morning later I had a smaller chunk of metal and a roughly fashioned base. I don't have a metal folding machine so the base was reshaped by brute force on the end of my workmate. It looks great from one side.

There is a solder pad on the PCB, a point you can ground to remove the bias for power down but I decided not to use it at the moment, for now I'll switch the 26volts. So not too much soldering was required just SMA in /outs, power supply and fan. It probably took longer to test and set up than it did to build, I couldn't take risks with this valuable amplifier.

The amp which is rated at 15 Watts has 30dB gain and Arthur had found his was most linear at around 4 Watts. My driver amp was to be the 7 Watt Minikits amplifier which up until now had been run as a low power PA. Some padding reduced the drive power to the 6dBm I was looking for.

In a hurry to get the project finished and working I didn't take many pictures of the build, below are a few just before the fan was wired.

On Thursday this week the PA was hooked up to my 2m DATV kit and it performed superbly.Our next test will be over a longer path to Ian G3KKD in Cambridgeshire.

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Monday, 09 February 2015 08:44

Power Amplifier for 2 Metres

Last week I located a class A power amplifier at a good price, it will be ideal for 2 Metre DATV. Rated at 15 Watts this is the same type used by Arthur G4CPE. Some work is required before I can use it as it's a pallet and needs heat sink and connectors.

My amplifier is coming from the Netherlands; its new old stock hence the good price. At the moment I feel like a kid at Christmas; looking out the window for a courier.

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Tuesday, 13 January 2015 00:00

2 Metre Band - NB DATV Contact

Using equipment seen in my earlier posts a 2 way NB DATV contact was completed on 12-01-14. My QSO with Arthur G4CPE was over a fairly short path; some 4.65 Kilometres.

During our contact powers as low as 200mW were used and signals remained solid throughout. Transmission mode was MPEG-2 at 543kS/s, and the QPSK encoder is a Link Research device with output at 70MHz. My DDS generates 216.500MHz and the two signals are mixed to 146.500Mhz and filtered before amplification by the PA.

Initial transmissions were carried out using collinear antennas. Over the next few day we will be carrying out various tests including some using horizontal polarisation.

Acknowledgements to Arthur G4CPE who supplied some of the components including a complete receive converter and lots of technical guidance. Thanks.

M0SKM

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Wednesday, 10 December 2014 11:17

Six Metre Upconverter for DATV

Several local radio amateurs with a keen interest in narrow band DATV have been carrying out tests in the six metre band. With a huge amount of help from Arthur G4CPE I now have transmit and receive equipment using modified commercial downconverters.

About six weeks ago I spotted a Continental Microwave downconverter on eBay, I knew it would be useful as Arthur (a former CM employee) had already briefed me on them. Described as new I decided to bid and got it for £35.00, it arrived with the security seals intact.

What's in the box?

The enclosure is double sided and contains a 70MHz IF board one side and a downconverter board in the second compartment. Conversion was originally 1GHz mixed down to 70MHz using the onboard 930MHz oscillator. There is an easily removable 1GHz filter on the input.

Reconfiguration for 50MHz Reception

In original form the downconverter output is connected externally to the 70Mhz IF input, this is very convenient as it allows us to retune the IF to 50MHz and reverse the process. Removal of the 1GHz filter from the converter input allows us to input 51.200MHz, mix at 930MHz and output at 981.2MHz, nicely in L Band.

Luckily the 1GHz filter is easily retuned to 980Mhz and used at the downconverter output.

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