Amplitude Modulation (microwave project).

Hi there.

I've a got a 4 ghz transmitter, but i'm struggling to design or find an amplitude modulation capable of modulating this type of frequency. Most amplitude modulation i'm seeing seem too low, in the range of 50 -100 Mhz frequency.
My question is, what range of frequency will be required to modulate this carrier frequency, bearing in mind i'm transmitting audio frequency.
Lastly, Please i will appreciate it if anybody can reccomend any amplitude modualtion circuit i can use (cause i can't find many).

Thanks in advance for reading.

any particular reason why you want to use AM ? FM is much easier to generate and demodulate

I have gear on many freq's from 1GHz through to 24GHz and FM is my mode of choice unless I'm
doing very weak signal work where I will use either SSB or CW

Dave

2FSK or 4FSK modulation is very easy, the signal can directly modulate on the VCO.

This is based on reviews from my peer suggesting amplitude modulation might be easier to implement, in comparison to phase modualtion, FM and PWM. Please can you send me FM modulation circuit capable of doing the job at this particular frequency. I'll appreciate it as well if you can send me amplitude modulation if you have one?

Thanks for your time.

---------- Post added at 00:27 ---------- Previous post was at 00:23 ----------

Hi tony. Thanks for replying. The problem is that, the binary or 4FSK modulation i've seen online so far seem not to work at that particular frequency. May be i'm doing something wrong.

P.S I'm a new to microwave.

---------- Post added at 00:28 ---------- Previous post was at 00:27 ----------

Hi tony. Thanks for replying. The problem is that, the binary or 4FSK modulation i've seen online so far seem not to work at that particular frequency. May be i'm doing something wrong.

P.S I'm new to microwave.

AM is really much more difficult to impliment
hence why all your microwave band video senders on 1.2, 2.4 and 5.7 GHz all use FM
As do us amateur radio ops for TV on uWave bands.

easiest way to FM a signal is by applying the audio to the VCO either to the tune volts pin or to the actual Vcc supply pin.
The PLL will try to keep that in check but you usually still produce enough variation to have a good FM signal.
I'm no expert in this field and cannot give you all the maths. I'm just a very practical experimenter :)

If you have a schematic of your system post it on here so we can see what you are dealing with

we need to see if you are using a LO and mixing it with an IF signal to produce your final TX freq. Thats the preferable way
That way you can have your VCO and PLL fixed freq and very stable and have a FM IF signal that you mix with it.

cheers
Dave

Low cost radio transmitters are in fact using a kind of AM: Simple ASK or OOK (on-off keying). It can be easily implemented at any frequency, but it's very unusual at 2.4 GHz, I think. You also have complex modulation techniques like QAM, but as you apparently targetting to simple methods, they most likely aren't an option. So FSK variants are the obvious choice, as suggested.

4FSK can be used till 40GHz. Surely it can be used at 2.4GHz.

ok here's a circuit I have had on my puter for a few years from one of my UK amateur friends
just to give you some ideas on what's involved :)

This one is for 2.4 GHz but with a change in VCO's you could use it on 5.7GHz
If you didnt want multi channel tuning you could do away with all the EPROMS etc
and just make it a fixed freq

cheers
Dave