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LAN_403

Erlend^SE

Sun Jan 24 2010, 05:18PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

I want a second option on a a project:

The idea is to build a radio-scanner based off a TV-tuner, and I have found a MSP3451G Multistandard sound processor in some TV (able to receive stereo FM modulated at around 10 MHz)

I also have 2 TDA-something based TV tuners (I2C), and wonder if I can just connect them to the sound processor.

Got audio-amps and speakers too, and the IC can do as audio router so more than one aux and and out is also tempting.

The control got to be via some microcontroller (AVR), and a display (VFD/LCD/LED).

Is this a feasible solution? and what problems may/will I encounter?

radiotech

Sun Jan 24 2010, 07:02PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

In the past I have found the old TV cable boxes, which provided a video/audio jumper plugs (so you could attach a MTS decoder were quite nice in that they used a DC input for tuning as well as another DC input to switch bands. connected to TV monitor, they made a TV set. I have seen projects to make them into spectrum analysers in the magazines. The only was those devices needed around 1000 microvolts input, as is cable levels. I also remember an AFC lock came back from the FM detector in the sound part. The boxes then returned the RF back to a TV on our channel 3 or 4.
The boxes showed up a thrifts shops for pennies.

Steve Conner

Sun Jan 24 2010, 10:41PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

"Together it will be like T + N + T.
The receiver is so powerful, you must use safetyglasses while using it!"

Dinges

Tue Feb 02 2010, 09:13PM

Registered Member #2511 Joined: Mon Dec 07 2009, 02:46AM
Location:
Posts: 36

I've used TV tuners (analogue, not I2C) in the past too for a panorama receiver from 47MHz-2GHz, and have built an experimental radio receiver too with a tv tuner (never got properly finished and boxed up, but worked fine; used a TV tuner, potmeter to vary tuning voltage (0-30V) and TDA7000 FM demodulator followed by LM386 audio amp).

I've put some pictures of the panorama receiver online: http://picasaweb.google.com/motorconversion/VariousProjects#5278153596704325074

(shows part of the FM band, with RX gain turned way down and using a screwdriver as antenna)

(analogue TV channel around 520 MHz)

Don't have any pictures of the wide-band radio receiver I built with a tv tuner; that was back in '90 or so, before digital cameras.

If you want the MF/LF part, you may want to have a look at this schematic of a 137 MHz weather-satellite receiver: http://picasaweb.google.com/motorconversion/VariousProjects#5282622146076002402, which also has a squelch circuit.

Though your IF needs to be at 38.4MHz - but I used a TDA7000 for that too in the panorama receiver, along with a SAW filter from an old TV receiver.

There used to be a project in Elektuur/Elektor long long ago (late '80s, I think), where they used an analogue TV tuner (Philips UV616S, from memory) as a wide-band radio receiver. Not sure it did scanning, but shouldn't be too hard to build something that does that and stops when the squelch opens. http://www.home.zonnet.nl/laar60/3.htm

Those TV tuners put out an IF of 38.4 MHz, so you'd need to convert that down to a lower frequency (the TDA7000 uses 70kHz, IIRC) and demodulate; keep in mind you may want to have separate demodulators for NBFM, WBFM and AM.

When I was building that panorama receiver I used an Icom R10 wideband receiver (scanner) tuned to 38.4 MHz for initial testing. Hold the antenna close to the tuner, and you can hear radio/tv stations as you tune the tuner around.

All in all it was a fun and educational project. Those TV tuners (especially the ones that can be tuned with an analogue 0-30V voltage) are handy little blocks that are easy to use, with many applications. But if it's low noise and decent intermod specs you're after, tv tuners won't work.

If it's just a working scanner you're after though, I'd recommend buying one.... as they're now compact and cheap. I love my Icom IC-R10 and IC-Q7 (smaller than a pack of cigarettes, receives from 30-1300MHz, and I can even transmit with it on 2m and 70cm). Buying is not nearly as much fun (and educational) as building though.

Peter.

Erlend^SE

Wed Feb 03 2010, 09:24PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Thanks Dinges, just the kind of reply I wanted :)

The FM demodulator-IC I plan to use have input at 10 MHz (there are other options too.. depending on what signal I select)

The tuner and the demodulator/sound processor IC are both I2C, so will be a small nice network :)

I will be examining the pages/links/schematics/pictures :)

uzzors2k

Sat Feb 13 2010, 02:16PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

This looks like a neat project! I've dismantled a battery powered FM/AM radio which used a ]TA2003P[/file] receiver chip, and I was lucky enough to find a schematic for a tuner using it. From here.

I knew nothing about radios before I saw this thread, so there's still some things I don't get however.

Most of the components I need are already in the radio, like the 10,7MHz filters and ceramic discriminator, but what are the other two Fget and 38MHz "quadcoils"? I understand that Fget is used to set the local frequency which is mixed to get 10,7MHz. But what is the point of the 38MHz box? And a little more practical, can these units be crystals or do I need to fine tune a coil/capacitor pair?

EDIT: I think the LC network on FM out is used to attenuate anything but the desired signal, in other words tune the receiver. Why put one of these in the circuit when the received frequency is constant and filtered I don't know yet.

GeordieBoy

Tue Feb 16 2010, 02:39PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

It looks like the receiver is a dual conversion type.

The tuner module "KS-H-148OA" mixes from "some frequency" down to a fixed IF frequency of 38MHz. The TA2003P (AM/FM Radio chip) has it's local oscillator "Fget" fixed at either 27.3MHz or 49.7MHz in order to mix the 38MHz frequency down to a second IF frequency of 10.7MHz. The tank circuit on pin 15 is used to suppress the image response of the second mixing stage, and the tank circuit on pin 13 is to set the frequency for the second local oscillator to either 27.3 or 49.7 MHz to convert 38MHz down to 10.7MHz.

The second IF is then filtered by the components hung between pins 3 and 8, and FM demodulated by the components at pin 10.

I would guess that a dual conversion scheme was used because the first tuner module is made to output an IF of 38MHz and the FM radio discriminator will only work with an IF of 10.7MHz.

Dual conversion is quite a common radio technique. It seems the Heterodyning was so good for radio reception, that they thought "why not do it twice!" Seriously though there are practical reasons why dual and tripple conversion can give better performance than a single conversion stage. Particularly where a very wide frequency spectrum needs to be covered in one continuous range, eg EMC testing receivers and scanners.

There is a block diagram of a dual-conversion receiver here:

and here

-Richie,

Erlend^SE

Tue Feb 16 2010, 06:19PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

I got a mixer IC that is called TDA9811, but if there is no video carrier there is nothing for it to lock on to?

Seems like I would NEED schematics for the RF stuff.. looks good from the links/pictures you fellow HV'ers have found :)

Any comment, is TDA9811 hopeless or can I use it to mix down IF from tuner (the broadcast network have gone digital, so nothing to see there)? or am I better off trying some PLL jig?

<= looks possibly like it may be an option? anyone knows?

I also got some SAW filters, useful?

101111

Wed Feb 17 2010, 06:07PM

Registered Member #575 Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263

You should check out NE612 and SA612/5..

Zeus

Wed Feb 17 2010, 09:29PM

Registered Member #2316 Joined: Tue Aug 25 2009, 03:04AM
Location: Bendigo, Australia
Posts: 107

Dinges wrote ...

If it's just a working scanner you're after though, I'd recommend buying one.... as they're now compact and cheap. I love my Icom IC-R10 and IC-Q7 (smaller than a pack of cigarettes, receives from 30-1300MHz, and I can even transmit with it on 2m and 70cm). Buying is not nearly as much fun (and educational) as building though.

That's why hamfests are great. I got a IC-R1 handheld scanner (with a good battery pack), which covers 0.1 MHz to 1300MHz for $120 AUD

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