FM/AM Tuner

[gpapag]

Hi forr
Thanks for the correction. I don't know what i do to the url addresses and they don't work. It is the third time I screw it up. ( had a few times i did it properly though)
At the said address, the comments for these tuners were very positive. I don't know what part of it is due to the specific topology, pulse count that is.
Regards
George

[gpapag]

Hi all
There are a few weeks now that I have received some FM Tuner kits (Larsholt LH7254) from Mr. Kiralyvalvy (“Kilary” see post#5). This is a superheterodyne receiver in a single sided pre-assembled PCB. Basic kit components are: TDA1062 front end IC, two broadband (250KHZ) IF ceramic filters, CA3189 IF IC (with a single discriminator coil), CA 741 for the AFC drive, CA 1310 stereo decoder IC.
A 100Kohm tuning potentiometer, 2 10Kohm trimmers, 2 resistors, 2 output cups, and a 12V DC PSU is what is required for a dry start.
Signal strength meter, Centre-Tuning meter, Stereo LED, Stereo/Mono switch, AFC On-Off switch, Mute On-Off switch (mute level adjustment is on board) can be directly wired to the appropriate output points of the PCB. (I tried them, they work OK). There is a buffered output for a frequency counter as well.
Kit arrived pre-adjusted with components for stabilized PSU, LED, RCA outlets and a few electrolytics generously supplied as a bonus.
For start, I tried it with a 12V 7.2 Ah lead battery.. With this loose implementation (80cm single wire for antenna, flying long leads), it works fine. 92mA consumption with LED and the two meters connected, 80 mA without. Around 600mV RMS AF output , superimposed on 800mV DC. Output cups required! It is stable, no drift even with AFC off.
In mono, very silent. In stereo there is a hiss (Scope trace shows 38KHZ remains and on strong modulation 57 KHZ as well). Compared in mono to a Tivoli, sound is more clean and detailed. Compared to a Kenwood KT-660L in mono and stereo, highs are clean, very good lows, detailed mids.
As is (I am in the process of doing some minor mods), the kit sounds very good. Easy to make it work and at a fare price as well. For a descent user-friendly tuner though, a 10 turns 100Kohm tuning potentiometer and a frequency indicator are required. I have ordered a Bourns potentiometer and I am in search for a cost effective way for implementing an appropriate frequency counter. Any help on this will be greatly appreciated.
Regards
George

[forr]

Hi Gpapag,

For modifications, it would be interesting to investigate for stereo decoders. I own TCA4500A board made by Velleman (ref 2553) and the Linsley-Hood sample and hold decoder. I currently can't make any comment, having not seriously installed them. I hope to do it soon.

I would be reticent about a digital frequency counter, fearing entrance of parasitic pulses in the tuner. Linsley-Hood published one a long time ago.

I have schematics for all of that, if you are interested, send me an email.

[gpapag]

Hi forr
Thank you for the help regarding frequency counter schematics. I appreciate. (you have blocked your e-mail from the forum. So, please e-mail me your e-mail address).
I have the same concerns for possible pulse-induced interference. Can you suggest any other means for having frequency indication using a 10-turns tuning potentiometer?
Regards
George

[rayfutrell]

I looked up those ICs at http://www.datasheetarchive.com/ . They are 30 year old circuits, so surely there must be newer ICs. Maybe Tamas has a newer design uning modern ICs.
Regards,
Ray

[forr]

Hi Gpapag,
Allow me a few days to scan the Linsley-Hood's article, it is very old, it is just for inspiration.
I modify my options so my e-mail should now be available. Some tuners have used simple coil meters as frequency indicators, the little difficulty lies in the writing of the frequencies scale.

[gpapag]

Hi Ray
Yes, Mr Kiralyfalvy has another kit with discrete FETs at the front stage and the 4500 as the stereo decoder. I may try it also. As for the TDA1062, he wrote me that he still prefers this IC due to it's good performance. CA3189 is a classic, proven design. The CA1310 is the one that shows it's age.
Forr
If i will be left with no other option (freq. meter), i will do it with the pulleys, strings and the needle. But i really prefer the direct precise freq. indication of a digital counter
Regards
George

[gpapag]

Ref Post #22
The DC at the audio outputs is 8V DC and not 800mV DC
Regards
George

[arensattic]

Hallo fellow DIYers,

Recently I have built a stereo FM tuner. An article about this project with literature references and schematics is posted on my website. The correct link is:

http://home.hetnet.nl/~a.van.waarde/id21.htm

The design dates from 1974 but all parts can still be purchased (in Holland, with exception of the Valvo FD-1A). Note that this is a cheap and simple tuner which can be easily reproduced, yet it performs reasonably well.

Greetings,

ArensAttic

[rayfutrell]

ArensAttic,
That circuit would have rather modest performance. You can show analytically that 6 tuned circuits are required in the IF for adequate alternate channel rejection and 4 tuned circuits are required in the RF amplifier for adequate image rejection. With ceramic IF filters so inexpensive there is no reason now for inadequate IF filtering. I don't know of any simple inexpensive solution for the RF filtering.
Regards,
Ray