DX TV Receiver
19-November-2002
Some changes to the overall design have been
made. I have found that it is difficult to
get the desired shape factor on the IF filters
that I would like. I've now included circuitry
that down-converts the tuner IF output to
a lower IF of around 15MHz. With the IF filters
at a lower frequency, I will be able to obtain
a far better shape factor. A block diagram
for the project has been upload in PDF format
and can be seen by clicking here
A new IF amplifier has been built using a TDA8341. I have an earlier IF amplifier design that is working, based on the Motorola MC1350 and MC1330 ICs. It uses manual IF gain control and has plenty of gain available for use with lossy filters. When I get time I want to try and build an IF strip using discrete MOSFETS and compare the performance to a strip using bipolar technology.
I have just purchased Todd Emslie's Icom R7000 - A great rig. Using a wideband noise source in conjunction with some software I put together I now have a rudimentary spectrum analyser. This makes it a lot easier to align and check the IF filter response.
Paul Barton, a UK-based TV DXer has contacted me. He has made some very useful suggestions, one of them being to consider using DSP (digital signal processing) instead of a conventional IF strip. It is something I'd been thinking of, having discussed it with somebody I know who is an expert in DSP systems. It offers many advantages over a conventional LC-tuned IF strip. Alignment is not required, and the IF response comes out exactly as the maths says it should. Variable bandwidth and tunable notch filtering is easily handled as well. The main drawback is cost, but I will look into it once the overall system is completed. As the system design is at present, an optional DSP system could be easily added. Paul has also suggested using a sync-separator IC to be used as a signal detector. He uses the output of the IC to turn on a video recorder on reception of a valid TV signal.
I'm still having problems locating a suitable low noise, digitally controlled TV tuner. If anybody can help, please contact me. Required tuner specifications and my email address are here.
Many thanks to those who have sent me comments and suggestions, please keep them coming. It is always easier to undertake a project like this when you know that people out there are interested in it.
5-October-2002
I've added a screen shot of the PC-based
control panel, plus some more information
on the DX TV receiver. Click here to see the panel plus a few notes regarding
operation. Todd Emslie has sent me a great
deal of very useful information over the
past few days. Now I just need the time to
go through it all - many thanks Todd.
1-October-2002
There has been a fair amount of interest
shown in this project and people have asked
me to put a quick and dirty web site together
so they can see what is happening, and provide
some feedback. Pictures and block diagrams
will uploaded soon - please be patient. Updates
to the site will be announced through the
ICDX Yahoo Groups news post. Any suggestions,
criticisms, suggested circuits etc can be
sent to me at sjandrew@bigpond.net.au or icdx@yahoogroups.com
The main thrust of this project is to design a portable DX TV receiver for the non-technical user, but at the same time, provide the experimenter with a modular system that allows the signal chain to be broken in various places to allow connection of external circuits such as tuners, filters, and IF systems.
The art of good design is to re-invent as few wheels as possible and in this respect I have (and will) crib unashamedly from past successful designs. Credit will be given to those who have done the hard work in the past. If you have any circuits you think may be of benefit to the project then by all means submit them. Hopefully, that way the project will get to use proven and successful designs.
I'd like to take this opportunity to thank Todd Emslie for his help. Todd has sent me a wealth of information that has proved invaluable - Thanks Todd :)
Progress so far
Progress to date has been encouraging. The
tuner being used for test purposes is a Phillips
UV1316 and is controlled using the Phillips
I2C serial bus protocol. Although the tuner
has a high noise figure, it does at least
allow me to test all software functions.
I'm still looking for a suitable tuner (and
other components) for the project - see below
I have a high-gain IF strip built, using manual gain control and a simple diode detector. At this stage I can receive TV signals and display them. There is currently no audio detection being carried out. The main work to be done now is with the IF strip. There are a lot of possibilities in this area and the hard part is going to be deciding on the best design using easy to obtain components as well as ease of setup and alignment.
The on-board micro-controller currently allows keypad entry of a frequency, and tuning of the entered frequency via a rotary encoder. Memory functions have also been included. The system can scan a set frequency block, or can scan selected frequencies entered into a bank of memories. An RS232 interface is included and software has been written that allow a PC to function as a virtual receiver with memory and scanning functions as well as a database of TV (and other) frequencies. Of particular interest is a spectrum analyser type of display to allow panoramic viewing of a block of frequencies. If a signal appears on the spectrum display, clicking the mouse on the signal will tune the receiver to that frequency.
So far there have been no problems experienced with the micro-controller causing interference. Care has been taken to ensure digital noise does not find it's way into the RF sections.
The following are a list of features I hope to include in the final design. Many are already included and working. All suggestions or criticisms are welcome:
RF Section
Manual RF gain control
Manual IF gain control - switchable to normal
AGC
The ability to connect additional filtering
between the tuner and the IF strip
Buffered IF output from tuner
Auxiliary tuner input to allow connection
of an external tuner
Variable bandwidth IF strip
Tunable IF notch filter(s)
1V PP Composite video output
Video output up-converted to a VHF or UHF
channel to allow viewing on a standard TV
Tunable audio de-modulator to allow reception
of various audio standards
Variable bandwidths on the audio demodulator
for NBFM reception
Inbuilt audio amplifier and loudspeaker
Audio output up-converted to allow monitoring
on an FM receiver
Signal strength indicator
BFO weak signal detector
Digital control section
Digital readout of receive frequency on LCD
screen
Keypad for direct entry of memory number
or frequency - 50KHz resolution
Standard rotary-type tuner control to tune
frequency or step through memories
Memory functions
Scanning functions
An RS232 interface to allow connection to
a PC - may also use USB
PC-based software to allow extended functions
and operation
TV Tuners and components required
Although I've been involved with electronics
design for some 15 years in Australia, it
has been with commercial and industrial equipment
so when it comes to TV, I'm in the dark as
far as component supplies are concerned.
If you know of any Australian or overseas
companies specialising in providing TV spares,
particularly TV tuners, or the Philips range
of TV ICs, I be would pleased to hear about
them.
I need to locate supplies of two types of TV tuner. Both tuners need to cover 45-850 MHz, **including hyperband**, should have as low a noise figure as possible, and preferably be available from a supplier in Australia.
One tuner should have manual varicap tuning, with a pre-scaled local oscillator output. The pre-scaled output may be divided by 64 or 256, if the pre-scaled output is selectable, so much the better. Band selection should be manual via pins on the tuner.
The second tuner should be a digitally controlled device using either a 2 or 3 wire serial link or the Phillips I2C bus protocol.
Any suggestions, data sheets or supplier
details will be most welcome.
Steve Andrew - Gold Coast - Australia
sjandrew@bigpond.net.au
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