receiving a carrier

No, that actually isn't your question.

You want to do something, and until you reveal that end game, any solutions are based on your interpretation of what you think is the solution.

Your asking about sending a signal, when the most basic design issue is what you want to do with that signal. "I want to tell Joe down the block that the coffee is ready" can actually have all kinds of solutions, some radio, some not. On the other hand, "I want to look at the transmitted radio signal on an oscilliscope" would have a different solution, and would come from a much smaller selection of solutions.

Reveal what it is you are trying to do, maybe a science project?, and then the solutions can come. It may not be what you think it is, because you've latched onto a solution that may not actually solve the actual problem.

Michael k

That is all the more reason to use an existing set of radio modules. Get ones designed for data input and output. They already meet the legal requirements for wherever you live, and you recover an exact copy of the transmitted signal. That is what modulation is, information encoded onto the carrier. This allows for a narrower receiver bandwidth. That reduces noise and other signals that can interfere with what you want to do. Turning a carrier on and off for modulation causes ringing and chirp, lowering the signal quality. transmitting is simple, but a good receiver design takes a lot of work. I designed my first receiver in 1968.

Jhon1,

I think you want someone to tell you that this has a simple solution and then give it to you.

Please try to understand, the folks here want to help.

But, the description given so far has not helped your cause.

This description is better, but still not enough.

I am sorry you don't understand radio systems. If you had any clue, the answers given so far would have been enough.

so, your problem still requires the width of the clock signal you wish to recieve to be given. Once that is known people here may be able to help you. Also how this clock signal is use will help.

The simpler the system the less accurate it will be.

Good Luck,

Donald

I agree with Michael T. -- radio modules would work quite well for this application if you're just looking to build a single unit and get something working.

Will that suffice? If not, if you actually *have to* design and build your own radio, from what you've said so far I think you're looking at a significant amount of work. One way to reduce this is to build at the "functional" level: Use filters, mixers, power amplifiers, etc. from the likes of Mini-Circuits, Hittite, Analog Devices, Maxim, etc.

Do you have a spectrum analyzer around? You can learn a lot by just hooking up an antenna (which can be as simple as a, say, foot long wire) and "sniffing" around -- you'll see your local radio stations, TV stations, etc. In your case, try something like the following:

-- Set a function generator to a frequency where it's *legal* to transmit in your country. Set the power to, say, 0dBm (1mW).

-- Connect an "antenna" -- just a wire, make it roughly 68/f mm long, where f is in MHz -- see

-- Connect another such antenna to a spectrum analyzer and find the transmitted signal

-- Move a few hundred meters away and see if you can still find the transmitted signal. If not, try bumping up the function generator's power output or adding an outboard amplifier... after you look up with the legal power limit is in the band you've chosen (here in the U.S., it's usually not more than 100mW or so in the unlicensed bands, unless you get fancy with spread spectrum techniques where you can have a watt).

Now... start trying to replace all that expensive test equipment with your own circuit!

The transmitter is almost always easier than the receiver, because you don't have to deal with interfering signals, absurdly weak power levels, etc.

If possible, you might want to get yourself something like an AM/FM radio kit to play with... something like

---Joel

Like the guy knows what a PLL is?"

What's the matter with you guys? The original poster won't understand 5% of he's being told.

Wait for his answers so he can be told something useful.

jhon1, Thanks for elaborating a bit on your application. It sounds like you need to regenerate a 100 MHz clock at some remote location that is a copy of the original. Depending upon where you live, it may not be feasible to transmit a 100 MHz carrier, because the local FM broadcast may interfere. The clock signal will need to be converted to a low rate information, and re-created at the receiver. To help further, some additional information is required:

Maybe you would get some better pointers if you could disclose the purpose of you application, as others have suggested... Chances seem high that a completely different approach would be optimum.

Frank Raffaeli

I think this is a wrong idea.

The sine wave transmitted will not arrive as sent, there will be distortion and other problems with the received signal.

Not every single sine wave will be recieved exactly.

But, good luck.

donald

Realistically he's looking to stick a narrowband filter at 100MHz on an antenna and measure the received signal's strength, and then use some (probably fixed) threshold to decide if he's receiving a carrier or not.

In other words, he's trying to do ASK as simply as possible. Obviously it won't be particularly robust, but it can certainly be done.

Oops, that should be OOK (on-off keying), not ASK (amplitude-shift keying), of course.

It works for the Morse code guys...

John,

Its very nice of you to keep everyone on their toes.

But, the discussion procedded nicely without bitching about top vs bottom posting.

Make you wonder if it really matters.

donald

They have the benefit of well trained ears to pick the signal out of the background noise, and most use a sidetone from a BFO, rather than raw clicks. Also, he is talking about a 100 MHz signal. Who could hear that? The best long distance telemetry available when I left the business was 40 Mb/s and cost $50,000 for the electronics on both ends. If he really needs 100 MHz square waves, his transmitter would have to be in the high GHz range.

What yoou are trying to dom is to set up an off-air frequency standard.

Your local national standards laboratory got there first.

Here is the 2.9 Mbyte describition of the US national off-air frequency standard.

This runs at 60kHz and includes a variety of modulations.

Other countries have similar sstems.

You'd want to set up two local nominally 100MHz clocks, probably based on a pair of volage-controlled crystal oscillators, and divide down the

The easy way to do this s to use on one the faster Analog Devices Direct Digital Synthesis (DDS) chips - the cheap parts won't take a

The AD9859 is faster and marginally cheaper and there are a number of other parts in the range.

Once you've got your duplicate of the off-air frequency standard you can compare it with an amplified version of the 60KHz signal coming out of some moderately selective radio receiver using - for instance - the frequency comparison circuit in a 4046 phase-locked loop IC, and use the analog voltage coming out of the converter to adjust the frequency of your nominally 100MHz voltage controlled oscillator to exactly

The advantage of this approach is that you don't have to broadcast your own frequency standard, which is likely to be illegal in most countries.

Hi Michael,

True... ears clearly don't function at 100MHz, although diodes do. :-)

I think today you could come close to that with off-the-shelf WiFi gear for If he really needs 100 MHz square waves, his transmitter would have to

I think he just wants to transmit sine waves; he says he's going to "squarise" (uggh... 2nd time I've heard that time, first was from Boki!) the sine waves on the far end "somehow." :-)

That would imply a horrendous amount of data.

BTW, the equipment I was talking about was for deep space work, and the entire bandwidth is recorded for later analysis. Not your everyday data link.

That's what I'm thinking, but his description sounds overly complicated.

It could also be interpreted as something like "I have this 100MHz standard and I want to make use of it", in which case an obvious question would be "why not use coax to connect the two".

One bit of followup description made me think he actually is modulating it, but he doesn't realize it is actually modulation. But that may just be my bad interpretation, since he's talking about waveform and that would be irrelevant if he's just needing to know that something is sending a carrier (but would complicate things if there is actually something he's sending that's important).

Obviously, if it's just the presence of a carrier that he wants to know about, a superhet does work fine (and since he dismisses the superhet, it's still not clear if he just misunderstands what he needs, or actually needs something that isn't clear from his description). Or any of a number of other receiving schemes that would easily provide information based on whether or not there is a carrier present on the frequency.

You're right, a simple scheme will provide no real indication of whether or not the signal he wants is the one that he's receiving, since with no form of modulation it could easily be some stray signal.

Michael