FM/AM Tuner

[lcsaszar]

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?

 

[lcsaszar]

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]

FM/AM tuner

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]

Re: Linsley-Hood tuner

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/showthread.php?postid=1807526#post1807526

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.

 

[lcsaszar]

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).

 

[Peter63]

Hi Kiraly,

Back in the early 1980s I was given a Larsholt FM module. I had it hooked up to a digital display and it worked very well. Unfortunately I cannot now find it ( I was a kid then!) and I would like to replace it. It had the following features:

Switchable IF sensitivity - I believe 3 choices but may have been 2
Switchable MPX filter On / Off
Switchable AFC On / Off
one aerial input
Output for digital frequency display

I think it may have been a LH7254 but I cannot be sure. I would be grateful if you could help me and I would be interested in the kits you have, especially if any of them use the module I had.

I look forward to hearing from you.

Best wishes

Peter

Newbury, UK

 

[al2002]

As the FM Bands are the same, it should work in Europe. It will not receive DAB, of course.

If you do not want to use a step down transformer, you may need to replace the internal mains transformer, or rig up an external power supply to replace the internal power supply.

The FM de-emphasis can be corrected by an external circuit.

Do a google search on this tuner and you will find these mods. Your search will also find users in the UK.

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.

 

[al2002]

I believe that Sony's software code is what gives this tuner its spectacular performance. Another maker's implementation of the chip set may well give inferior results.

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).

 

[al2002]

PS:- If my two examples are typical, this tuner's AM performance is nothing to get excited about. Find yourself an old Lowe HF-150/225 series radio, or a modern Palstar, to listen to for good quality AM reception.

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.

 

[giralfino]

tuner kit

Hi all,
I listen to the radio a lot, so I'm thinking of building a little FM mono tuner + amp + speaker for my working room.
The idea is to build a small box with the tuner + amp with only two knobs for volume and tuning. I'm searching a small tuner that can be paired with a small amp like this one: small amp on ebay
Any ideas where to find such a tuner? A frequency display would be great but not necessary, only a knob for tuning is required.
Advice on amps are also welcome.
TIA, Ralf

 

[UnloadedQ]

Hi all,
I listen to the radio a lot, so I'm thinking of building a little FM mono tuner + amp + speaker for my working room.
The idea is to build a small box with the tuner + amp with only two knobs for volume and tuning. I'm searching a small tuner that can be paired with a small amp like this one: small amp on ebay
Any ideas where to find such a tuner? A frequency display would be great but not necessary, only a knob for tuning is required.
Advice on amps are also welcome.
TIA, Ralf

Probably the best chip for an analog tuner is the Philips TDA70XX series. The TDA7000/7010/7088 are all extremely simple and app notes on making them go are provided. The coils used are extremely simple and no IF transformers are needed. These chips all use a lower IF frequency suitable for stereo reception based on active bandpass filters built into the chips. One pot is all that's needed for operation.

For a more ambitious tuner, go for the Silicon Labs chips like the SI47XX series. The 4704 and 4731 are more complex, but the SI4731 comes with a complete demo board with an LCD requency indicator and AM loopstick antenna, etc. Not sure of the cost of the demo board, but it's a damn decent digital FM tuner chip (no programming needed for the demo).

If you're not afraid of getting dirty with some digital, any of the PIC micros can talk to the Silicon Labs chip as well as another, possibly the simplest, FM tuner chip in existance. The Philips TEA5880. This is a complete FM stereo tuner that needs exactly 2 external components, L1 and L2, both 0.38nH inductors that can be simple spirals of PCB tracks. SMT inductors can also be used. The PIC (or any suitable microcontroller that can emulate a simple 3 wire serial port) can set the frequency of operation and generate a readout, get the stereo pilot and so forth. This is another low IF based FM tuner like the TDA7000 series, but one heck of a lot better performance. You can add a buffer front end as shown in the TDA7000 series app notes using an untuned inductor and a BC849 transistor (any suitable VHF transistor).

Most of the parts can be had from Digikey or Mouser or Future Electronics.

The USLs for Philips and Silicon Labs.

NXP Semiconductors
Silicon Labs - leader in high-performance, analog-intensive, mixed-signal ICs.

 

[EUVL]

I am afraid that your information given above is not quite up to date.

Firstly none of the parts mentioned above are on stock at DK or Mouser (only listed), except for the SI4731 Demo Modules at around 60 USD. The TDA chips were originally Philips, but since they became NXP, they sold that business to ST, and ST has put most of the TDA70xx stuff obsolete. There are only a handful of dealer who still have stock.

The SI chips are all one chip tuner, which means they use varicaps and caps integrated in the IC. I have build one of these with a JFET analog output stage :

Mini-Stereo-RDS-Radio-Modul Fertiggert, bernsteinfarben | ELV-Elektronik

It is again all digital with lots of features, but the sound was so-so even with a discrete output stage.

Then I built one using the TDA7021/7040 according to datasheet / Elektor :

Mini VHF FM Receiver - ELEKTOR.com | Electronics: Microcontrollers Embedded Audio Digital Analogue Test Measurement

but replace all SMD ceramic caps with MKP or mica, and also added an opamp amplified output stage. It sounds fantastic for the cost and the simplicity. The key is the choice of discrete components.

I will build a JLH FM next year, but that is a LOT more effort than this.


Just my own personal experience,
Patrick

 

[tinkerbelt]

I see you have a few surface mount components on there. Presumably you could have used ordinary bits instead? I've not done much hand soldering of surface mount but I know it's not easy.

 

[danielwritesbac]

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 Sony XDR-F1HD .

Oh, perhaps its fine if you have really bad quality speakers. Sure the tuner itself is fantastic, but the audio section is sheer junk. It even clips itself!

Quality varies per sample as to how much treble you're going to get, as it varies between slightly insufficient or far too much.

The unit is designed, like most electronics of today, as a short-life easy-bake oven so that you'll have to buy something else in a few years, when it commits suicide due to heat. An external power supply may be a consideration, since the included power supply is inefficient, causing additional heat.

A quickie fix for heat is to put on some of the extra tall rubber feet and enlarge the plastic vent holes by cutting out every other plastic louver, making half as many vent holes at much larger size. Speeding up the airflow that way does just happen to work decently.

What you get for your $100 is one the best RF sections made, teamed up with a lot of junk that needs fixed. The AF section is very bad quality. Its not just noticeable, its execrable. Documentation on exactly how to do the necessary upgrades is pretty scarce due to lack of photos that show exactly where to connect what. So, the many projects with this tuner are indecipherable except for people who are already capable of building their own tuners. Ironic.

The scan, tune, features on the unit and its remote are somewhat inappropriate until you set up the presets. The presets work great, but for one appalling exception. The memory lasts only a couple of minutes during a power outage, so this thing forgets all that work you just put in to get it set. So, this also needs an upgrade.
As a bonus, it has the "blinking zeros" clock that runs, with a light up panel, even when the unit is off. And yes, that needs fixed too.

When a station has a borderline signal strength between digital or analog, the Sony HD will merrily bounce back and forth, and when that's going on, it doesn't make a useful audio presentation. Its possible to upgrade this behavior with a mechanical switch installed somewhere, which could lock the tuner to analog.

And, the point. . .
Well, a plain old superhet, if given a rather elegant booster with filtering and a slightly more substantial antenna, is going to perform a lot better for Audio, with no significant increase of difficulty. In the case of the Sony, there's an excellent RF section and the rest needs an overhaul--a whole slew of band-aid fixes upon miniature circuits. However, in the case of the handmade tuner, the RF section is some effort but audio quality may be easier.

Or, a better point. . .
Since its hard to purchase a table radio with an excellent speaker and AF section, a handmade project with either handmade tuner or a tuner-board product, plus some excellent DIY audio, can make a presentation exactly as desired by its owner. This isn't available in stores.

 

[LAJ]

I built the TDA7000.

Its different, and drifts a little bit. But it lacks the nice things like digital tuning. But its great for a fixed tuned receiver.
Never used them, but I heard the ZN414, 416 make a good AM receiver. They're TRF tuners which eliminates the bandwith restriction of IF stages. Would probably sound pretty good on a strong signal.