RF transceiver chips with low-kHz bandwidth?

[Joerg]

Hi Guys,

Looking for a transceiver chip with low IF bandwidth, sub-1GHz. All the
usual suspects I have canvassed can't be set below about 50kHz
bandwidth. This leads to a poor link budget for very small data rates
and we'd only need a few bits per second. Modules are too expensive, got
to stay under $3 for chip plus surrounding parts, in k-quantities. Any
ideas?

Reason is we need lots of range, >1000ft if possible with stub antennas
and ideally no more than 10mW because that's the limit in many
countries. With that requirement 2.45GHz is pretty much out,
unfortunately. Of course I can roll my own analog version but a chip
would be so nice. Something with a kHz BW or so, that has the smarts to
see-saw across a range so it can catch a carrier without needing
super-stable oscillators and such. I can do the see-saw scans with a uC
if needed.

Oh, and we'd need something from a reputable supplier that can actually
supply. Know what I mean ...

 

[Robert Lacoste]

Hi Joerg,

Look for the ADF7021-N from our dear friends Analog Device... IF bandwidth
down to 9KHz, 2,88$.

Friendly yours,
Robert Lacoste
www.alciom;com

 

[Joerg]

Hi Joerg,

Look for the ADF7021-N from our dear friends Analog Device... IF bandwidth
down to 9KHz, 2,88$.

Merci beaucoup, Robert. It won't get to the single digit kilohertzes but
does go down to 12.5kHz. That's a lot better than all the others with
50kHz. The price is a bit high and it has a stiff package which isn't so
great if gear gets banged around but it sure beats all the other chips
in performance so far.

 

[Robert Lacoste]

Any idea how well it does detecting Amplitudinous Modulation (true
AM)?

Jim

No, sorry, we used it only for FSK
Robert

 

[Joerg]

No, sorry, we used it only for FSK

Robert, what kind of range did you get with it? And what sort of antenna
(length)?

 

[Robert Lacoste]

Robert, what kind of range did you get with it? And what sort of antenna
(length)?

Well, we used an ADF7021-N for a VHF system (169MHz telemetry band), so
range was, well, long (around 20km open field, some km in urban
environments), so I guess this experience will not be transposable to
yours... By we way we wrote a small white paper on advantages of 169Mhz for
telemetry, in case someone is interested :
http://www.alciom.com/en/Downloads.htm

Yours,
Robertt

 

[Jon Kirwan]

Well, we used an ADF7021-N for a VHF system (169MHz telemetry band), so
range was, well, long (around 20km open field, some km in urban
environments), so I guess this experience will not be transposable to
yours... By we way we wrote a small white paper on advantages of 169Mhz for
telemetry, in case someone is interested :
http://www.alciom.com/en/Downloads.htm

Thanks. I've been following the discussions in this thread
and learning from them. The paper connected some things I
learned about elsewhere (Friis formula, though in somewhat
different form from eetimes and mpdigest in 2007 authored by
ADI employees) and anticipated would come up in your paper as
I read it. And they did! The worked details were nice, too.

thanks,
Jon

 

[Joerg]

Well, we used an ADF7021-N for a VHF system (169MHz telemetry band), so
range was, well, long (around 20km open field, some km in urban
environments), so I guess this experience will not be transposable to
yours... By we way we wrote a small white paper on advantages of 169Mhz for
telemetry, in case someone is interested :
http://www.alciom.com/en/Downloads.htm

Excellent paper, Robert. Unfortunately we can't do 500mW. Well, on
900MHz and inside the US we can and sometime do but that won't fly at
all in Europe. Especially not in France ;-)

I like VHF just like you do, much better for longer range
communications. That is why I completely fail to understand why many of
our TV stations gave up their VHF channel for a UHF channel, without
putting up a fight.

 

[Joerg]

Nobody lets you use external filters any more? Or does that blow the
budget?

They don't let you. I guess that designing external filters is expecting
too much these days so they poured it into the silicon. Or maybe
engineers just don't want to fuss around with this and rather treat it
as a digital building block. Probably for the same reason many people
won't or can't drive a stick shift anymore.

Sometimes I wonder about the transceiver chip market -- mostly it's "Are
those guys really that much smarter than me? Or are they that much
dumber?" (It's got to be one or the other).

It's like with TV set, things are being dumbed down. Heck, ours won't
even let you add channels. You can only run a clean slate scan and there
are few days when more than 95% of channels will "stick".

 

[Rich Grise]

It's like with TV set, things are being dumbed down. Heck, ours won't
even let you add channels. You can only run a clean slate scan and there
are few days when more than 95% of channels will "stick".

You should run the channel scan after dark - propagation conditions are
much better then.

Cheers!
Rich

 

[Joerg]

You should run the channel scan after dark - propagation conditions are
much better then.

Not out here. We even stopped taping movies if they do not run during
the day. After 7:00pm numerous channels begin to pixelate. Sometimes we
were sure a movie stuck, only to discover that it froze into a Picasso
painting 1h into the movie #@&*!!

Our TV consumption has dropped significantly since DTV was foisted upon
our nation. Same for many neighbors. Analog was better, much better.
OTOH it had some good effects, more real socializing among neighbors.

 

[Joerg]

You're thinking HF -- at VHF, and especially at UHF, there's not enough
ionization in the upper atmosphere to bend (or bounce) the radio waves.

Unless a slew of little meteorites hisses out up there

 

[Rich Grise]

You're thinking HF -- at VHF, and especially at UHF, there's not enough
ionization in the upper atmosphere to bend (or bounce) the radio waves.

Maybe it's just here then. During the day, channel 50.x doesn't come in
worth beans, but at night it's about the strongest one in the range.

How about tropospheric bending by the thermocline?

Thanks!
Rich

 

[Joerg]

Maybe it's just here then. During the day, channel 50.x doesn't come in
worth beans, but at night it's about the strongest one in the range.

How about tropospheric bending by the thermocline?

Maybe it's the smog?

DTV reception quality does not have much to do with field strength. The
ATSC protocol appear to be so shakey that the slightest multipath
reflection can toss it off the rocker. Sometimes when my wife says that
we probably can't watch or tape anything because the stations all
blue-screen I look at the spectrum in my lab. And sure enough, they're
all there, nice and strong. But undecipherable :-(

 

[Jeroen Belleman]

Thanks. I've been following the discussions in this thread
and learning from them. The paper connected some things I
learned about elsewhere (Friis formula, though in somewhat
different form from eetimes and mpdigest in 2007 authored by
ADI employees) and anticipated would come up in your paper as
I read it. And they did! The worked details were nice, too.

Ah, the Friss formula for free space path loss, which states
bluntly that this path loss is proportional to frequency...
If that were true, then light wouldn't ever get anywhere, now
would it?

Of course, free space path loss simply goes as r^2. No frequency
term in there. No one ever seems to notice that Friss defines
his effective antenna apertures as a fixed number of wavelengths!
In fact, he's supposing smaller and smaller antennas as the
frequency goes up. No wonder the amount of received power
drops!

Jeroen Belleman

 

[Charlie E.]

Feds prolly bribed them with tax breaks...

No, it is because OTA transmissions don't bring in any money, while
cable and sattelite rebroadcast does. You just need to broadcast
anywhere to get the rebroadcasters to give you money...

Charlie

 

[Joerg]

No, it is because OTA transmissions don't bring in any money, while
cable and sattelite rebroadcast does. You just need to broadcast
anywhere to get the rebroadcasters to give you money...

That's what staion owners think but they are missing part of the
picture. And so so chief engineers. I talk to one whose station lost a
chunk of coverage when they gave up VHF. His argument was that UHF does
penetrate buildings better. Ahm ... they've all got cable down there in
the city.

The folks with more disposable income, a.k.a. prime targets for ad
revenue, do not live there. They live in the suburbs. Many purposely do
not have satellite of cable because they don't want the TV to dominate
family life. But they do watch the news, or used to. That's where
reception became unreliable. So what do those people do? They upgrade
their Internet for more megabytes/sec, watch the news there, and
subscribe to Netflix. Viewer numbers for stations shrink, ad revenue
shrivels up, personnel costs need to be reigned in. Some of the latter
is clearly noticeable by now.

 

[Charlie E.]

That's what staion owners think but they are missing part of the
picture. And so so chief engineers. I talk to one whose station lost a
chunk of coverage when they gave up VHF. His argument was that UHF does
penetrate buildings better. Ahm ... they've all got cable down there in
the city.

The folks with more disposable income, a.k.a. prime targets for ad
revenue, do not live there. They live in the suburbs. Many purposely do
not have satellite of cable because they don't want the TV to dominate
family life. But they do watch the news, or used to. That's where
reception became unreliable. So what do those people do? They upgrade
their Internet for more megabytes/sec, watch the news there, and
subscribe to Netflix. Viewer numbers for stations shrink, ad revenue
shrivels up, personnel costs need to be reigned in. Some of the latter
is clearly noticeable by now.

Yes, and this used to matter for ad prices and such, but now that the
majority of viewers are on cable/sat, the stations don't care as much
anymore... :-(

Charlie

 

[Joerg]

Yes, and this used to matter for ad prices and such, but now that the
majority of viewers are on cable/sat, the stations don't care as much
anymore... :-(

You'd be surprised how many people out here are not on sat/cable. And
those tend to be the ones with well-paying jobs, meaning disposable income.

However, there is a trend that the media moguls seem not to grasp and
this one is much more serious: The kids of those folks. Once they head
off to college many forego TV altogether. Internet and Netflix is all
the rage there. I know several who don't even have a TV anymore, they
watch everything via their computers.

 

[josephkk]

Hi Guys,

Looking for a transceiver chip with low IF bandwidth, sub-1GHz. All the
usual suspects I have canvassed can't be set below about 50kHz
bandwidth. This leads to a poor link budget for very small data rates
and we'd only need a few bits per second. Modules are too expensive, got
to stay under $3 for chip plus surrounding parts, in k-quantities. Any
ideas?

Reason is we need lots of range, >1000ft if possible with stub antennas
and ideally no more than 10mW because that's the limit in many
countries. With that requirement 2.45GHz is pretty much out,
unfortunately. Of course I can roll my own analog version but a chip
would be so nice. Something with a kHz BW or so, that has the smarts to
see-saw across a range so it can catch a carrier without needing
super-stable oscillators and such. I can do the see-saw scans with a uC
if needed.

Oh, and we'd need something from a reputable supplier that can actually
supply. Know what I mean ...

Thread read. Just the same, can you add (modulate with) some nice
predicable PRN thus using the extra bandwidth to your advantage?
Regulatory issues may make hash of this idea.