Use of separated FM receiver module from SONY theater system

[Willen]

Hi, I got a retired SONY blue ray home theater system. It looks advanced. I found a small FM receiver module inside. I don't know if I can use it or not. I am excited because it has coax antenna connector and maybe impedance of around 50 ohms unbalanced (EDITED). I have never used 50 ohms antena based FM receiver. Excited because I can make some dipole and yagi as a test with this type of 50 ohms antenna based system. Possible?

 

[AnalogKid]

Commercial FM receivers, like those for broadcast TV, use 75 ohm coax or 300 ohm twinlead.

ak

 

[Nigel Goodwin]

Yes, 75 ohms is normal for radio or TV coax - but the problem with the board is the software to control it, it's almost certainly software driven via I2C bus or similar. In my experience you also can't get datasheets for the IC's used, so you've no idea of how to control them.

 

[JimB]

it has coax antenna connector and maybe impedance of around 50 ohms balanced.

As AK has already commented, is more likely to be intended to be 75 Ohm, but, in reality the input impedance will probably not be well defined as 75 Ohm and will vary across the frequency range from 88 to 108 MHz.

Will this be a problem? No.

However, as for being "balanced" coax cable circuits are not balanced.
For a balanced circuit you need twin feeder type cables.

Something which may be a big problem for you, the tuning information for the receiver arrives down the ribbon cable as digital information from a microprocessor.
If you cannot recreate that data, you will not get much sense out of that receiver board.

JimB

 

[unclejed613]

Something which may be a big problem for you, the tuning information for the receiver arrives down the ribbon cable as digital information from a microprocessor.
If you cannot recreate that data, you will not get much sense out of that receiver board.

according to the pic of the top of the board, it's I2C.... if the receiver still works somewhat, you could connect an I2C "sniffer to the board, and record the data sent for tuning the module and work out what the instructions are... or find another Sony receiver in a similar model or around the same time frame of manufacture, and record the I2C data from that.... i've seen the insides of many Sony receivers, and unless it's a major change of technology, sony rarely re-invents the wheel.... their "low-to-mid" range of models have used the same main PC board for many years...


using 50 ohm antenna designs to feed a 75 ohm input is really not a problem, you lose about 1 to 2 dB of sensitivity from the slight mismatch. if you are building yagis, you will gain more than that back.

 

[Nigel Goodwin]

according to the pic of the top of the board, it's I2C.... if the receiver still works somewhat, you could connect an I2C "sniffer to the board, and record the data sent for tuning the module and work out what the instructions are... or find another Sony receiver in a similar model or around the same time frame of manufacture, and record the I2C data from that.... i've seen the insides of many Sony receivers, and unless it's a major change of technology, sony rarely re-invents the wheel.... their "low-to-mid" range of models have used the same main PC board for many years...

Perhaps it's different over there?, but as an ex-Sony service dealer I've seen the insides of a great many as well - and unless they are the same model, they are entirely different from each other. Historically Sony didn't keep models for more than a year, and each year would be a completely different.

The I2C data would depend entirely on the exact tuner module, and the PLL IC fitted, and they never seemed very standard across models - but any 'later' Sony audio gear tended to be made in China, if not actually designed in China as well.

using 50 ohm antenna designs to feed a 75 ohm input is really not a problem, you lose about 1 to 2 dB of sensitivity from the slight mismatch. if you are building yagis, you will gain more than that back.

If you're buying an unbalanced FM aerial, then it's going to be 75 ohms anyway, as far as I'm aware they don't make 50 ohm ones?. And if you're building one, then simply build a 75 ohm one. You don't want to lose a couple of dB, if you're using yagis (and why wouldn't you?) you're probably looking for long distance reception anyway (I used to use an 8 element yagi, on a rotator). If you're in a strong area, and only want local stations, a bit of wire is all you need.

I used to use a Grundig R-45 receiver, which was incredibly sensitive on FM, and out performed any Japanese receivers I ever tried. The R45 was a VERY expensive unit, but we got them (and huge amounts of other Grundig gear) dead cheap, as we took the entire stock from the Irish division when it was closed, after the boss was murdered by the IRA terrorists.

 

[Willen]

Things are getting complicated. I even do not know more about I2C. Some question arose:

1. Why FM receiver like R-45 was very expensive? Because of its high price rate, it should be pretty strong and amazingly sensitive. The main question: do they use secret ICs to make it extra ordinary? Cannot we add RF signal amp (like attached below) to make few dollar radio super sensitive?
2. As I know cheap few dollars FM receiver has different type of antenna impedance (like 20 ohms?) and I cannot feed 50 or 75 ohms antenna to them? Any alternative to use dipole or Yagi to dollar radio?

 

[Nigel Goodwin]

Things are getting complicated. I even do not know more about I2C. Some question arose:

1. Why FM receiver like R-45 was very expensive? Because of its high price rate, it should be pretty strong and amazingly sensitive. The main question: do they use secret ICs to make it extra ordinary? Cannot we add RF signal amp to make few dollar radio super sensitive?

No 'secret' IC's, just good design, in particular good selectivity and plenty of tuned circuits at the front end. If you want to look, the schematic is at:

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1. As I know cheap few dollars FM receiver has different type of antenna impedance (like 20 ohms?) and I cannot feed 50 or 75 ohms antenna to them? Any alternative to use dipole or Yagi to dollar radio?

You can feed anything you like in - it just won't work as well as proper imedance matching, but those cheap receivers aren't intended for that anyway. But they aren't 20 ohms, it's going to be HIGHER than 75 ohms, but unspecified as it's not of any relevance, and probably never measured or calculated (as there's no point).

 

[unclejed613]

Perhaps it's different over there?

quite different, their whole low-mid priced receivers all use the same main PCB, populated with more components and inputs/outputs the farther up the price scale they go. they use the same belly pan that they've been using for years for these models, with one change, they finally got rid of one of the mounting points for the "L" shaped part of the board that has the ribbon cable connection to the front panel. that mounting point would crack the board right across the traces going from the ribbon connector to the MPU if the receiver was dropped more than a few inches. when i would replace a board i would bend that tab down. finally Sony figured it out, and deleted that mounting tab by cutting it off...

 

[Nigel Goodwin]

quite different, their whole low-mid priced receivers all use the same main PCB, populated with more components and inputs/outputs the farther up the price scale they go. they use the same belly pan that they've been using for years for these models, with one change, they finally got rid of one of the mounting points for the "L" shaped part of the board that has the ribbon cable connection to the front panel. that mounting point would crack the board right across the traces going from the ribbon connector to the MPU if the receiver was dropped more than a few inches. when i would replace a board i would bend that tab down. finally Sony figured it out, and deleted that mounting tab by cutting it off...

VERY different then, presumably Sony(USA) source them direct rather than through Sony - most probably bought in from China and badged.

Interestingly, Sony(USA) are active in the UK, they are the source of Play Stations, which are nothing to do with Sony(UK), as a Sony dealer we couldn't even buy Play Stations - and back when Sony had a manufacturing plant in the UK (in Wales), Sony(UK) sourced their TV's from Sony(Spain) rather than the UK plant.