Semi OT: History of consumer radio designs

I'm interested in how the design of consumer AM/FM radios has
 evolved over time, particularly since digital tuning/ PLL
 synthesizers came on the scene.  Some early (1980?) PLL receiver
 schematics I've seen show the LC front end tank being tuned by a
 varactor diode.  I'd imagine for several reasons one would want
 to eliminate the complexity of this kind of front end setup if at
 all possible.  

I'm guessing that modern consumer receivers are just an IC using
 direct conversion? But from what I've read direct conversion
 wasn't mature enough technology to use for FM until fairly
 recently.  So how did the general design evolve from the simple
 superhet to what we have now over the past ~35 years?




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On Tue, 9 Dec 2014 20:18:01 -0500 (EST), bitrex
<bitrex@de.lete.earthlink.net> Gave us:

>I'm interested in how the design of consumer AM/FM radios has
> evolved over time, particularly since digital tuning/ PLL
> synthesizers came on the scene.  Some early (1980?) PLL receiver
> schematics I've seen show the LC front end tank being tuned by a
> varactor diode.  I'd imagine for several reasons one would want
> to eliminate the complexity of this kind of front end setup if at
> all possible.  
>
>I'm guessing that modern consumer receivers are just an IC using
> direct conversion? But from what I've read direct conversion
> wasn't mature enough technology to use for FM until fairly
> recently.  So how did the general design evolve from the simple
> superhet to what we have now over the past ~35 years?

  Ever heard of Joe Walsh of "James Gang", and "The Eagles" (and solo)
fame?

  He has a pretty nice collection.  Maybe these are not the radios you
are looking for...

https://www.google.com/#q=joe+walsh+radio+collection

On Tue, 9 Dec 2014 20:18:01 -0500 (EST), bitrex
<bitrex@de.lete.earthlink.net> wrote:

> I'm interested in how the design of consumer AM/FM radios has
> evolved over time, particularly since digital tuning/ PLL
> synthesizers came on the scene.  Some early (1980?) PLL receiver
> schematics I've seen show the LC front end tank being tuned by a
> varactor diode.  I'd imagine for several reasons one would want
> to eliminate the complexity of this kind of front end setup if at
> all possible.  

In the 1980's, we had synthesized local oscillators and digitally
tuned stereo receivers.  Progress for most of the 1970's was getting
rid of mechanical parts involved in the receiver tuning.  That meant
microprocessor push button control of the PLL.  However, the IF and
discriminator circuits were largely unchanged throughout the 1970's
and 1980's.  What also changed was the inexorable drift from discrete
to integrated designs.  Large sections of the circuitry were size and
cost reduced down to individual IC's.  

During the 1990's, most of the RF, IF, demod, and audio circuitry was
crammed into a single IC, surrounded by a few discrete components, and
run by a micro.  However, the receiver was still fundamentally an
analog design full of LC and ceramic filters.

> I'm guessing that modern consumer receivers are just an IC using
> direct conversion? But from what I've read direct conversion
> wasn't mature enough technology to use for FM until fairly
> recently.  So how did the general design evolve from the simple
> superhet to what we have now over the past ~35 years?

Fairly recently would be about 2005.  That's when DSP receivers
changed everything.  For example:
<http://www.silabs.com/applications/audio/Pages/AudioVideoReceivers.aspx>
At the same time, the audio section went digital with a Class D
switching power amplifier.  The only part that's still linear was the
added AGC (automatic gain control) at the front end required to keep
the input level stable enough to use all the available bits.

Somewhere along the time line, sub-carrier data, HD Radio (IBOC),
RDS-TMC arrived.

I'm sure I left out quite a few details...
-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

On 10/12/2014 01:18, bitrex wrote:
>
> I'm interested in how the design of consumer AM/FM radios has
>   evolved over time, particularly since digital tuning/ PLL
>   synthesizers came on the scene.  Some early (1980?) PLL receiver
>   schematics I've seen show the LC front end tank being tuned by a
>   varactor diode.  I'd imagine for several reasons one would want
>   to eliminate the complexity of this kind of front end setup if at
>   all possible.

The transition to stereo decoding in the 1970's was also fairly 
interesting with the early chips and discrete modules having a lot of 
very finickitey coils and tuning capacitors that had to be just right. 
ISTR MC1310 was the first easy design to use in homebrew kit.

In the UK Ferranti made modules that various high end makers like 
Roberts plugged together in a chassis to make consumer radios. Then 
there were the ubiquitous miniature Japanese transistor radios.

Clive Sinclairs Micro-6 was also notable way back in 1964 as the 
smallest radio in the world. Fun webpage about it at:

http://s206301103.websitehome.co.uk/sinc.miniradio.htm

> I'm guessing that modern consumer receivers are just an IC using
>   direct conversion? But from what I've read direct conversion
>   wasn't mature enough technology to use for FM until fairly
>   recently.  So how did the general design evolve from the simple
>   superhet to what we have now over the past ~35 years?

Interestingly modern FM tuners do not seem to have improved their 
performance much beyond state of the art in the 1980's. The front end 
sensitivity might be a bit better but the distortion is sometimes worse.

What we have now at least in the UK is DAB broadcasting at a bitrate 
that produces a sound quality inferior to FM (although to be fair it 
does reproduce the inter programme gaps with a lower noise floor).

The fun bit is in borderline areas of DAB reception voice breaks up so 
that the newsreader sounds like the subterraneans on Stingray gargling 
whilst trying to read the news. Every now and then the bitstream crashes 
the decoder chip completely. I have given up on it at home in favour of 
internet radio where the signal quality and bitrate is high enough for 
studio quality on Radio 3 and way better than DAB on Radio 4.

One fun feature of modern DSP is that you can repurpose a cheap digital 
TV dongle as a wide band radio scanner by using alternative drivers and 
mutilating its firmware a bit. Become a new hobby for some folk.

-- 
Regards,
Martin Brown

On a sunny day (Tue, 09 Dec 2014 18:47:49 -0800) it happened Jeff Liebermann
<jeffl@cruzio.com> wrote in <3mbf8a9lkvlntier45k8cp3t8icsp3viut@4ax.com>:

>Fairly recently would be about 2005.  That's when DSP receivers
>changed everything.  For example:
><http://www.silabs.com/applications/audio/Pages/AudioVideoReceivers.aspx>
>At the same time, the audio section went digital with a Class D
>switching power amplifier.  The only part that's still linear was the
>added AGC (automatic gain control) at the front end required to keep
>the input level stable enough to use all the available bits.
>
>Somewhere along the time line, sub-carrier data, HD Radio (IBOC),
>RDS-TMC arrived.
>
>I'm sure I left out quite a few details...


One or 2 years ago I bought a Tecsun radio:
 http://www.ebay.com/itm/111288607108

It is based on the Silabs S-4730 chip,
BROADCAST AM/FM/SW/LW RADIO RECEIVER
dataheet here:
 https://www.silabs.com/.../TechnicalDocs/Si4730-31-34-35-D60.pdf


It is an amazing receiver, use it everyday.
Look at the block diagram.

Jeff Liebermann <jeffl@cruzio.com> Wrote in message:
> On Tue, 9 Dec 2014 20:18:01 -0500 (EST), bitrex
> <bitrex@de.lete.earthlink.net> wrote:
> 
>> I'm interested in how the design of consumer AM/FM radios has
>> evolved over time, particularly since digital tuning/ PLL
>> synthesizers came on the scene.  Some early (1980?) PLL receiver
>> schematics I've seen show the LC front end tank being tuned by a
>> varactor diode.  I'd imagine for several reasons one would want
>> to eliminate the complexity of this kind of front end setup if at
>> all possible.  
> 
> In the 1980's, we had synthesized local oscillators and digitally
> tuned stereo receivers.  Progress for most of the 1970's was getting
> rid of mechanical parts involved in the receiver tuning.  That meant
> microprocessor push button control of the PLL.  However, the IF and
> discriminator circuits were largely unchanged throughout the 1970's
> and 1980's.  What also changed was the inexorable drift from discrete
> to integrated designs.  Large sections of the circuitry were size and
> cost reduced down to individual IC's.  
> 
> During the 1990's, most of the RF, IF, demod, and audio circuitry was
> crammed into a single IC, surrounded by a few discrete components, and
> run by a micro.  However, the receiver was still fundamentally an
> analog design full of LC and ceramic filters.
> 

Thanks for the reply.  I'm still curious how in these later
 designs the input filter was tuned to be offset from the LO by
 the IF frequency; I don't think they're using variable caps or
 diodes. I think I'm missing something - when you have have a PLL
 synthesized LO is there a way that the need to tune the front end
 filter can be eliminated

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On 10/12/14 20:47, Jan Panteltje wrote:
> One or 2 years ago I bought a Tecsun radio:
>   http://www.ebay.com/itm/111288607108
> It is based on the Silabs S-4730 chip,
> BROADCAST AM/FM/SW/LW RADIO RECEIVER
> dataheet here:
>   https://www.silabs.com/.../TechnicalDocs/Si4730-31-34-35-D60.pdf
> It is an amazing receiver, use it everyday.
> Look at the block diagram.

Jan,

Do you know what CPU drives the Si4734 chip?

Asking because I have a couple of Si4735 chips here, including a 
software patch from the manufacturer for SSB reception (under NDA), with 
the intention of building an 80m direction-finding receiver with them. 
I'm not sure that the RSSI/AGC steps will be small enough. Even 0.1dB is 
a big enough step to be annoying for DF when using "whoopee" mode, so 
I'll probably have to rectify the audio and produce my own RSSI. Luckily 
the AGC limits, step size, and delays are software-settable, so I could 
just use that for auto-ranging, and the post-AGC RSSI for whoopee. 
Otherwise the AGC can be put under full software control anyhow.

The PL360 is a nice format, and with a modified antenna would suit DF 
use very well, as long as the CPU is reprogrammable/replaceable and 
there's room to add the whoopee circuit. Whoopee is essential, no-one 
wants to be looking at RSSI numbers while waving an antenna around in 
the scrub.

Clifford Heath.

Thats easy
You use the same control voltage that the pll creates to drive the vco varicaps, to tune the front end filter varicaps.
With proper design you can use the exact same voltage, the tuned circuits are scaled such that it all tracks pretty well.

Mark

On a sunny day (Thu, 11 Dec 2014 12:38:08 +1100) it happened Clifford Heath
<no.spam@please.net> wrote in <Cz6iw.1066865$yK.1035193@fx14.iad>:

>On 10/12/14 20:47, Jan Panteltje wrote:
>> One or 2 years ago I bought a Tecsun radio:
>>   http://www.ebay.com/itm/111288607108
>> It is based on the Silabs S-4730 chip,
>> BROADCAST AM/FM/SW/LW RADIO RECEIVER
>> dataheet here:
>>   https://www.silabs.com/.../TechnicalDocs/Si4730-31-34-35-D60.pdf
>> It is an amazing receiver, use it everyday.
>> Look at the block diagram.
>
>Jan,
>
>Do you know what CPU drives the Si4734 chip?

Well, as you asked I tried to have a look:
 http://panteltje.com/pub/Tecsun_inside_1_IMG_4685.JPG
The CPU (or FPGA??) is under the metal cover that is soldered,
did not want to rip that apart.
 http://panteltje.com/pub/Tecsun_inside_2_IMG_4684.JPG
Seems like it could be a PIC:


>Asking because I have a couple of Si4735 chips here, including a 
>software patch from the manufacturer for SSB reception (under NDA), with 
>the intention of building an 80m direction-finding receiver with them. 
>I'm not sure that the RSSI/AGC steps will be small enough. Even 0.1dB is 
>a big enough step to be annoying for DF when using "whoopee" mode, so 
>I'll probably have to rectify the audio and produce my own RSSI. Luckily 
>the AGC limits, step size, and delays are software-settable, so I could 
>just use that for auto-ranging, and the post-AGC RSSI for whoopee. 
>Otherwise the AGC can be put under full software control anyhow.
>
>The PL360 is a nice format, and with a modified antenna would suit DF 
>use very well, as long as the CPU is reprogrammable/replaceable and 
>there's room to add the whoopee circuit. Whoopee is essential, no-one 
>wants to be looking at RSSI numbers while waving an antenna around in 
>the scrub.
>
>Clifford Heath.

Yes, for sure it is a pity this radio does not have an SSB mode.
For that I have an Tecsun PL600 (longwave through shortwave + FM).
I have the circuit diagram for that, but quite different, does not use the Si4730 chip:
 http://elektrotanya.com/tecsun_pl-600.pdf/download.html


Anyways, you could control the Si4730 with a PIC I think,
you can even make PWM audio with a PIC:
 http://panteltje.com/panteltje/pic/audio_pic/
But the PL360 has an analog volume control, some DA must be in it somewhere.
What I do not see in the Si4730-31-34-35-D60.pdf data sheet is the registers to program the chip.
Without that data it will be next to impossible to program it from some micro.
(Well almost impossible, we have ways of finding out).
Do you have that register data under non-NDA?

On 11/12/14 22:02, Jan Panteltje wrote:
> On a sunny day (Thu, 11 Dec 2014 12:38:08 +1100) it happened Clifford Heath
> <no.spam@please.net> wrote in <Cz6iw.1066865$yK.1035193@fx14.iad>:
>> Do you know what CPU drives the Si4734 chip?
> Well, as you asked I tried to have a look:
>   http://panteltje.com/pub/Tecsun_inside_1_IMG_4685.JPG
> The CPU (or FPGA??) is under the metal cover that is soldered,
> did not want to rip that apart.
>   http://panteltje.com/pub/Tecsun_inside_2_IMG_4684.JPG
> Seems like it could be a PIC:

That seems fairly likely. thanks for looking. A friend has
used a PIC32 for his, which does triangulation from GPS
measurements.

>> Asking because I have a couple of Si4735 chips here, including a
>> software patch from the manufacturer for SSB reception (under NDA),
> Yes, for sure it is a pity this radio does not have an SSB mode.

If I can get the patch I'm sure you can too.
It's a encrypted data file to program the internal
DSP, so knowing the registers is not enough; you
need to be able to produce the DSP code and encrypt
it.

We got the SSB patch because for DF use, you tune to
maybe 1KHz off the fundamental CW signal to get a
heterodyne whistle.

The DSP uses a very low IF; 45KHz I believe. Keeps the
power consumption down :)

> Anyways, you could control the Si4730 with a PIC I think,

Yes. I have several possibilities I'm thinking of:
MSP430 (cheapest/low-power), STM32 ARM7 (to implement IMU
and drive a colour LCD), or an FT245 USB chip in bit-bang mode
(for prototyping from the desktop computer). I was thinking of
trying the last one first, because I have a couple of alternate
front-ends to try.

> What I do not see in the Si4730-31-34-35-D60.pdf data sheet is the registers to program the chip.
> Without that data it will be next to impossible to program it from some micro.
> (Well almost impossible, we have ways of finding out).
> Do you have that register data under non-NDA?

Also under NDA I believe, but just ask, they're pretty helpful.
As I said, not useful without the DSP and encryption data anyhow.
It would be excellent if they opened that up.

Clifford Heath.