FM/AM Tuner

[oshifis]

I read somewhere that the best FM demodulator is the "scaler demodulator". It is practically a one-shot circuit triggered by the FM signal. Since this type of circuit works below a few MHz, the usual 10.7 MHz IF signal has to be mixed down, using a second L.O. One can use a 10 MHz oscillator, so that the second I.F. would be 700 kHz. The frequency variation will cause amplitude fluctuation after low-pass filtering the pulse train. The conversion is ultra-linear. Has anybody heard of any commercial design that uses this principle?

[dxer_87]

The fact is that the main problem (affecting on receiver quality) is the RF stage, which is disregarded in typical, commercial applications (and the hardest part). I've heard that two ore more IF freq. change the quality, and I think there would be no problem to find some apps. But! it's another eccentrity, while we can have near the same effect with more ceramic filters or narrow band filters. (that's why in 70's Kenwoods they put up to 5 CF filters!). Even with this (as some say: old) 3189 chip there are 4 filters.

Engineers built many IC's for RF and IF stages, but the difficulty is with LC elements. With high freq. everything is different (no linearity, elements have great influence on each other, skin effect etc.). We say in Poland that the 'devil is in details'. And more coils = better characteristics, but more coils=harder to tune it together.

If we talk about analog there is a limit with 'what you can get'. Even with the best of the best tuner you are limited with antenna system (another neglected thing).
With 2uV tuner you're able to get half Europe with good antenna... (and with no ant. only local stations).

I bought today a little fm receiver with auto-tune (these TDA7xxx chips). And in some cases it's excellent (city) and another is useless (bus, train). You're asking why? Because in Taiwan they cut costs counted in parts of cents. With a few more elements you're able to get very good parametres, but when silly americans and europeans would buy this, what's the problem?

So, who says, that common people with soldering gun can't beat them?

[oshifis]

Here is an example of the pulse counting receiver I mentioned before:

http://www.users.bigpond.com/cool386/pcrx/pcrx.html

[jeje]

Hello,

Here it is.

I just find my hard copy of Fm decoder.

http://rapidshare.de/files/47461530/st_r_o1.pdf.html
http://rapidshare.de/files/47461553/st_r_o2.pdf.html

Is that all.

Best regards

jj

[Tinust]

I thought, let's kick up this topic. Anybody any information about the Larsholt frontend (number on the pcb 8045 B). This one is gone and I need a replacement or a spare.

Regards,

Martijn

[urbanebassman1]

Originally posted by forr
Hi Urbanebassman1,

I can help you with some schematics. Just email me.

---to a possible match for the output of a Leak Troughline valve tuner?---
Do you mean a stereo decoder ?

Thanks for your kind offer Forr, the schematics would be of great help.

Yes, my original idea was to build the Linsley Hodd stereo decoder to convert the mono mpx output of my Troughline 3 to stereo.
I liked the design because the audio signal path was kept separate from the decoder IC.

My new email address is given in my profile.
Regards
Martin

[rayfutrell]

Here is a review of the SONY XDR F1HD FM tuner that sells for $100 and uses DSP to achieve performance you could only dream about using analog circuitry. This is why nobody is going to offer a DIY FM tuner kit. you can't beat this performance for $100. See the review at http://www.ham-radio.com/k6sti/xdr-f1hd.htm .

[al2002]

Absolutely correct.

See my post above:

http://www.diyaudio.com/forums/showt...26#post1807526

Originally posted by rayfutrell
Here is a review of the SONY XDR F1HD FM tuner that sells for $100 and uses DSP to achieve performance you could only dream about using analog circuitry. This is why nobody is going to offer a DIY FM tuner kit. you can't beat this performance for $100. See the review at http://www.ham-radio.com/k6sti/xdr-f1hd.htm .

[djsb]

Hi,
Can this tuner be used in the UK? The UK uses the DAB system not hybrid digital, but could the tuner still be used to receive standard AM and FM transmissions?
I've seen them listed on Ebay but they are only available from US sellers and I'm not sure if they can be used on a 240v supply.
Anyone in the UK have any experience of this tuner?
Thanks.

David.

[oshifis]

No direct experience, but I see two problems here:

- It works from 110V/60Hz. Operating the unit from a step-down transformer still gives 50Hz, which will cause the internal tranformer run too hot. I've read the receiver has internal overheating problems.
- It uses 75 us deemphasis, we need 50 us.

Since it uses NXP (ex Philips) chipset, I can not imagine there is no European version (maybe not Sony, but some other firm may produce an RDS+ capable or RDS upgradeable set).