am transmitter - vlsi project

[john jardine]

[...]

You can look at it as "multiplication" or "mixing"-- both are at least
partially correct.

But if you look at the output waveform on a scope, you have this
waveform where the RF amplitude gores UP and DOWN, all the way down to
ZERO, so in some sense the carrier sure LOOKS like it's going down to
zero. And if you think of the B+ voltage going to zero, it's hard to
imagine how the carrier can still be going out when the plate voltage
is zero.

So it's at least partially incorrect to say the carrier "stays the
same" and "sidebands pop up".

Just read this post while currently receiving grief from a scope versus
spectrum analyser contest.
I'm checking the levels and frequencies coming out of a balanced mixer
design being fed by 2 audio frequencies. All was well until I made a mod to
the wiring on the protoboard. Bugger!, lost the mixing products and was
just left with 2 audio frequencies. Mixer output still looked fine on
scope so spent next 15 minutes chasing up the problem. A few mins ago found
I'd miswired the audio and was looking at a 'real' mixing of 2 signals,
hence no multiplier products on the SA.
What's troubling me is that the scope was leading me along me by showing a
neat and clean DSBSC signal. Tweeked the frequencies a little and the scope
moved to a 'normal' mixed audio-on-audio signal.

Can't leave well alone, so wired the (asynchronous) 50ohm audio sources to
10K resistors with their junction to the scope and started looking for audio
mixtures that 'look' like DSBSC. To this end I dropped the frequencies down
to see the scope spot tracking across the screen (0.5 sec per div =no visual
artefacts) and am now looking at a nice DSBSC signal that I know isn't a
DSBSC signal. It's 4Hz 2Vpp and 4.4Hz 2Vpp. It all adds up in the wash but
aint half a confusing time waster!.
john

 

[Joerg]

Hallo Anno

They're glass under steel. The tube itself is a more-or-less
conventional glass tube, apart from the stubby shape. I sawed
one apart as a youngster. Didn't quite make it, the hood *is*
steel.

That's the challenge. If the tube is really unobtanium which it most
likely is for us here in the US I'd have to figure out how to get
another tube in there or, ideally, come up with a semiconductor
solution. Since the socket is so odd one would have to cut off a tube to
make a plug. This is hard to do in a safe manner. But compared to when
we were youngsters at least now we have access to stuff like diamond
blades and wet saws.

 

[Michael A. Terrell]

Hallo Anno


That's the challenge. If the tube is really unobtanium which it most
likely is for us here in the US I'd have to figure out how to get
another tube in there or, ideally, come up with a semiconductor
solution. Since the socket is so odd one would have to cut off a tube to
make a plug. This is hard to do in a safe manner. But compared to when
we were youngsters at least now we have access to stuff like diamond
blades and wet saws.

Try asking in There are a lot of people
there that collect and restore antique test equipment, and someone may
have the tube you need.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Ancient_Hacker]

Hallo Anno

That's a toughie-- you could use an Australian 6G7, or a USA 6SF7,
they're both remote cutoff pentodes and two diodes. A bit high on
transconductance, so you might need a 100 ohm resistor in the cathode
lead. Ugh.

You will have to make an adapter socket- those funny german p-base
sockets are mighty rare.

 

[Joerg]

Hello Michael,

Try asking in There are a lot of people
there that collect and restore antique test equipment, and someone may
have the tube you need.

Good idea. Although I don't see this thing as a valuable antique, more
like an old tractor that I'd like to put to use again. So maybe I just
scrape all the tube stuff out and build a nice solid state oscillator
around the rather elaborate and top notch LC circuitry in there. That
would probably leave 95% of the enclosure unoccupied and reduce the
power consumption by 95%

 

[Joerg]

That's a toughie-- you could use an Australian 6G7, or a USA 6SF7,
they're both remote cutoff pentodes and two diodes. A bit high on
transconductance, so you might need a 100 ohm resistor in the cathode
lead. Ugh.

That would be no problem. An Aussie tube would restore the balance out
here. Had to replace the IF tube in my old Astor BPJ with a German tube
about 15 years ago. It hasn't developed an accent yet

You will have to make an adapter socket- those funny german p-base
sockets are mighty rare.

Might be better to tear the tube stuff out of there, keep the nice LC
circuitry and build something modern around that. I mean, it's just a
level-controlled oscillator and amp. Although I'd like to maintain its
whisper quiet phase noise behavior.

 

[Rich Grise]

Hello Rich,
[Joerg snipped whoever said this; Joerg, would you please fix your
neweader's attribution?]

Joerg ... tell me it isn't SO!!!! I've got a whole stockroom full of
6146s that will never fulfill their destiny.

[this was me:]
Just gold-plate their bases, and sell them to audiophools for $900.00
apiece. ;-)

And don't forget fancy plate connectors to go with them. Maybe like a
small moped cylinder with gold plated fins, with an official endorsement
paper from the RST Institute, Audio Research Department

http://www.mgs4u.com/RF-Microwave/tube-sockets.htm

2/3 of the way down the page: "Heat Dissipating Plate Caps" ;-)

Cheers!
Rich

 

[Joerg]

Hello Rich,

http://www.mgs4u.com/RF-Microwave/tube-sockets.htm

2/3 of the way down the page: "Heat Dissipating Plate Caps" ;-)

That's the ones. But instead of ultra-high efficiency they should be
gold-plated with some outrageous claim as to how many dBs they will be
better than anything else on the planet and the whole galaxy.

 

[Ancient_Hacker]

Rich Grise wrote:

2/3 of the way down the page: "Heat Dissipating Plate Caps" ;-)

That's not as crazy an item for some of those high-power tubes--
the datasheets suggest you keep the metal to glass seals at under 200C
if you want them to continue to hold vacuum.

Now those "Stereo imaging cones" to put under your equipment.....

 

[Rich Grise]

Hi,
I need to design an AM transmitter as a vlsi project (it needs to be
located on smart dust later on).
Does anyone have any good suggestions were to start from? I am familiar
with vlsi, but don't really know how to implement such a big idea, into
a vlsi simulation and circuit design.
Looking on trasmitter's schemes didn't help, 'cause that's all
resistors, amplifiers and capacitors. How do I translate it into vlsi
design?
Be very glad to any guidance...

Has anyone who's been following up on this thread said anything practical
about generating this on VLSI?

Because I was just now sort of musing - the Xilinx XC9500 CPLD can be
clocked at fantastically high frequencies (well, fantastic to a guy who
grew up with inductors wound on a toilet paper tube), like "system
frequency up to 178 MHz."
http://direct.xilinx.com/bvdocs/publications/ds057.pdf

With that kind of speed, writing a PWM to modulate a class 'D' 1 MHz with
1 KHz should be a walk in the park.

I'm actually not sure if I've said that right.

I'd have a 128 MHz internal clock, and a programmable divider down to 1
MHZ (for example), and PWM that: 50% duty cycle with no modulation input,
and so on.

If you have an analog input, you'd have to digitize it, but if you're
making it up, you can generate whatever you want.

Have Fun!
Rich

 

[joseph2k]

http://www.bdcast.com/fgal/white_paper/4MX_White_Paper_4M_Modulation_BCEWHP.pdf

Interesting, a digital modulation approach takes 72 stages, presumably of
equivalent output power? Doesn't that yield a pretty poor dynamic range?

Or is it a 72-bit D/A, which sounds totally crazy.

And they must be in perfect phase and at perfect power levels across the
band.

SioL

On the digital modulation described:
Unless i really missed my guess, it is a lot like old class B, C linear rf
amplifiers. One amplifier running class B taking care of the power dips
and a class C amplifier doing all the plus work. Something like 57 percent
efficient, and broad band capable.
Of course if the step size is about 1.20 to 1 it could give you a fairly
linear 60 db modulation range.
Also the on-off switching seems to be at least at carrier frequency, making
this some kind of modified class S amplifier.

 

[jasen]

That's the challenge. If the tube is really unobtanium which it most
likely is for us here in the US I'd have to figure out how to get
another tube in there or, ideally, come up with a semiconductor
solution. Since the socket is so odd one would have to cut off a tube to
make a plug. This is hard to do in a safe manner. But compared to when
we were youngsters at least now we have access to stuff like diamond
blades and wet saws.

how to fabricate plugs:

stick a layer (or two) of polyethelene sheet (from a plastic bag) over the
socket through the sheet poke suitabley sized pins into the socket
so that they go suffiiciently deep into the socket, and protrude atbout 10mm.
apply 6mm thickness of automotive body filler (or similar two-part putty)

when it's almost set trim the edges with a knife.

I can't vouch for the delectric strength of the putty, but if it's an issue
apply heatshrink to the pins before the putty.

Bye.
Jasen

 

[Joerg]

Hello Jasen,

how to fabricate plugs:

stick a layer (or two) of polyethelene sheet (from a plastic bag) over the
socket through the sheet poke suitabley sized pins into the socket
so that they go suffiiciently deep into the socket, and protrude atbout 10mm.
apply 6mm thickness of automotive body filler (or similar two-part putty)

when it's almost set trim the edges with a knife.

I can't vouch for the delectric strength of the putty, but if it's an issue
apply heatshrink to the pins before the putty.

Cool! That might also be a nice method to make other connectors that
have gone obsolete. Then someone pulls it some day and see a Walmart
logo from the bag on the bottom. Ah, that's where I can buy these...

Dielectric strength shouldn't be an issue. I bet that Bondo and stuff
like that would be quite good but I'd have to throttle the "plate"
voltages anyhow when changing over to FETs. Most dual-gate RF FETs can't
stand more than about 12V on the drain.

 

[Joerg]

Hello Rich,

Has anyone who's been following up on this thread said anything practical
about generating this on VLSI?

Because I was just now sort of musing - the Xilinx XC9500 CPLD can be
clocked at fantastically high frequencies (well, fantastic to a guy who
grew up with inductors wound on a toilet paper tube), like "system
frequency up to 178 MHz."
http://direct.xilinx.com/bvdocs/publications/ds057.pdf

With that kind of speed, writing a PWM to modulate a class 'D' 1 MHz with
1 KHz should be a walk in the park.

I'm actually not sure if I've said that right.

I'd have a 128 MHz internal clock, and a programmable divider down to 1
MHZ (for example), and PWM that: 50% duty cycle with no modulation input,
and so on.

If you have an analog input, you'd have to digitize it, but if you're
making it up, you can generate whatever you want.

The OP eventually wants to integrate this into a tiny bare chip. Keep in
mind that FPGA at high clock rates almost need a direct link to the next
electricity plant.

 

[Michael A. Terrell]

Good idea. Although I don't see this thing as a valuable antique, more
like an old tractor that I'd like to put to use again. So maybe I just
scrape all the tube stuff out and build a nice solid state oscillator
around the rather elaborate and top notch LC circuitry in there. That
would probably leave 95% of the enclosure unoccupied and reduce the
power consumption by 95%

Where is the challenge in that?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida