[SOLVED] Low cost signal generator

[SIGI44]

I would like to buy a RF signal generator in the range 3 to 4 Ghz.
Unfortunatly I have not the money to buy it now. (we've a lot more taxes to pay now in Italy !)

A the moment my need is to have a signal generator offering a level at least an average of -10 dBm (don't care the flatness of the signal level)
I have a specrum analyzer ReS and using the Tracker at 0 span I get a signal generator in the range 100Khz-3Ghz (signal level out is 0 dBm)
I have also a good RF generator in the range 100 Khz-1.2 Ghz (max level out 7 dBm)

Anyone can tell me if using a mixer (wich mixer ?) and mixing the two signals can I obtain a signal from 3 to 4 Ghz (at least - 10 dBm)
If yes, thank you in advance for the info about the mixer I have to use.

Giovanni Siccardi

 

[biff44]

If it were me, I would not waste my time, but would instead try to find a cheap sweeper on ebay for maybe $500.

 

[SIGI44]

Hello Biff44 (by the way if 44 mean the year of your birth, we have the same age),

Thank for Your advice, but I prefer not to spend money this way. I've learned at my expenses that if you buy something on this price range, the money is last forever because when You want to resell it You can't. Not to tell about the possibility to be swindled on the net. And also You must consider that in Europe we have less low price offer than on the States.
If You buy something good quality, good brand, more expensive You can resell it when you want without difficult.

For this reason I'll wait some months until I have more money to efford this expense.
In the meantime if somebody has an answer for my original question is welcome.
Thank you

 

[ALERTLINKS]

In some cases first harmonic can be tracked and used.

 

[SIGI44]

First armonic of what ? If yo're talking about the Rohde e Schwarz armonic, well, the armonics are inversely proportional to the price payed for the instrument.
And I can tell that it is absolutely not a cheap instrument...

 

[ALERTLINKS]

No! sorry, I was sleepy. Its about second harmonic or third harmonic from your signal generators which fall in your desired frequencies.

 

[BradtheRad]

Anyone can tell me if using a mixer (wich mixer ?) and mixing the two signals can I obtain a signal from 3 to 4 Ghz (at least - 10 dBm)

Rather than a mixer, perhaps you mean a frequency doubler. It's a circuit that detects the transitions (going up and down) in the incoming waveform. You end up with 2x the original frequency. You only need to tune one waveform generator.

Another common method has been mentioned in preceding posts. It requires that you tune two units.

You construct an LC tank circuit which can be adjusted to resonate at the frequency range you desire.

Connect it, inductively (or some way that provides a degree of isolation) to your existing generator.

You will tune the LC tank to a *harmonic* of a square wave from a lower frequency coming from your generator. (It cannot be a sine wave because sine waves don't have harmonics.)

The harmonic might be at 3x or 5x. The LC tank picks up that harmonic, causing it to resonate as a sinewave.

So you can amplify it as a sinewave, or clip it so it becomes a square wave.

 

[SIGI44]

Hi, BradtheRad,

I have a good frequency doubler, but I need at least 3 dBm having it to work. Now you must consider that I've the signal generator max 1.2 Ghz , level out 7dBm and with this it works fine, but I get only a max 2.4 Ghz out. With the other generator (I use the tracking generator of the Rohde e Schwarz spect Analyzer at 0 span , I get only 0 dBm out and the frequency doubler doesn't work).
Much more interesting your second proposal. Well tomorrow ...

thank You very much

 

[biff44]

If you can live with a CW source, I have had good luck with these. They are only $300 and go to 4.4 ghz. As a bonus, there are two independent outputs.

Products

 

[SIGI44]

Thank You biff44.
it seem a good solution

 

[biff44]

Make sure you get the usb card too to program them!

 

[SIGI44]

Hi biff44,

Of course... they offer two
I've choosen the one with the right socket
Thank You again

 

[Mazz]

That's a nice solution, but it's just a small extension of what you can get directly from an EVAL board from the major RF synthesizer manufacturer, ADI, Hittite, Linear, National Semi and, in some extension ST Micro.

This product are developped for cellular basestations, SDR, Microwave Links and the spectral purity required by this systems is really high.

Take a look at Hittite Hittite Microwave - HMC833LP6GE, PLLs with Integrated VCOs : this is a very good product, you can have a very small frequency resolution, low spurs and low phase noise, lower, in some case, respect to signal generators!

The drawback is that the use of frequency dividers brings to high level of harmonics (at very low frequency the output is an almost perfect square wave).

The eval of these synths is a good option, although they do not provide any labview driver, you have to build it by yourself (very time consuming).

Mazz