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'[EE] Difference between waveform generators'
2007\07\29@014739 by Matthew Bajor

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I was wondering, what is the difference between a function generator and an
RF signal generator, besides the frequency . Does it have ONLY to do with
the higher frequency or something else such as the lack of waveforms besides
an ordinary sine? Basically, I am looking to buy a Wavetek 2407 and want to
make sure I am getting a piece of equipment that can put out an RF carrier
sine wave without an input and without modulation.

Thanks

Matt Bajor

2007\07\29@032511 by Dario Greggio

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Matthew Bajor wrote:
> I was wondering, what is the difference between a function generator and an
> RF signal generator, besides the frequency . Does it have ONLY to do with
> the higher frequency or something else such as the lack of waveforms besides
> an ordinary sine?


I usually considered a "function generator" as something that can create
several waveforms at several frequencies (maybe RF too, and modulation
can be an option too)
while a "RF generator" is IMO just a sine-wave generator for RF, with
several types of modulation.

--
Ciao, Dario

2007\07\29@103445 by Herbert Graf

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On Sun, 2007-07-29 at 01:47 -0400, Matthew Bajor wrote:
> I was wondering, what is the difference between a function generator and an
> RF signal generator, besides the frequency . Does it have ONLY to do with
> the higher frequency or something else such as the lack of waveforms besides
> an ordinary sine? Basically, I am looking to buy a Wavetek 2407 and want to
> make sure I am getting a piece of equipment that can put out an RF carrier
> sine wave without an input and without modulation.

I don't know if it's a strict definition, but in general:

- function generator - usually generates more then just sine waves, at
least in addition to sine some square waves. Often others (ramps,
triangles), and also often modulation of those waves (i.e. FM, AM, PWM).
May generate into the RF region, may not.

- RF generator - usually only generates sine waves, but perhaps offers
more modulation choices. At the most basic I'd expect at least AM and FM
modulation. Obviously generates in the RF region, and usually doesn't do
anything for lower frequencies (i.e. 20kHz).

TTYL

2007\07\29@110301 by Jack Smith

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Herbert Graf wrote:
{Quote hidden}

It may also be worth adding that function generators tend to be dirtier
in terms of broadband noise, phase noise, etc. than RF signal
generators, at least in my experience.

A lot depends on the specific models, of course, and not every function
generator has worse phase noise than every RF signal generator, but for
most receiver measurements I would not generally use a function generator.


Jack

2007\07\29@160312 by Richard Prosser

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RF Generators also usually provide some sort of (reasonably accurate)
attenuator and have some way of setting the output to a known output
level e.g. 0dBm.

Function generators often only provide a gain control and cannot
reliably output a low level signal. External leakage/ radiation is
also likely to be higher (,although the cheaper RF sig-gens can be bad
here also).

RP

On 30/07/07, Jack Smith <spam_OUTJack.SmithTakeThisOuTspamcox.net> wrote:
{Quote hidden}

> -

2007\07\30@062538 by Alan B. Pearce

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> I was wondering, what is the difference between a function generator and
> an
> RF signal generator, besides the frequency . Does it have ONLY to do with
> the higher frequency or something else such as the lack of waveforms
> besides
> an ordinary sine?

I would expect a function generator to be able to provide sine, triangle and
square waves at a range of frequencies, but the frequency accuracy may not
necessarily be highly accurate, 1-5% or so. The sine output may not be
terribly pure, i.e. it is likely to have significant harmonic content, and
the distortion level may not be very low, as this is often generated by a
low pass filter off the triangle wave signal. The output level is likely to
go to several volts, with a general purpose attenuator, again of not very
high accuracy, and may have a TTL square wave output as well for syncing
other instruments. If you want frequency and level accuracy you would set
this with external instruments to monitor the output.

An RF signal generator would have better frequency accuracy and stability,
along with a calibrated output level and attenuator. The output level is
likely to be a maximum of 1V into 50 ohm, and with the attenuator go down to
the uV region, and have a properly shielded case so there is no signal
leakage from elsewhere in the instrument at this output level. The spectral
purity of the output will also be a lot better, with any harmonics being
typically better than -60dB on the fundamental frequency.

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