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'[EE]: Signal generators - Agilent 33220A or Tek AF'
2008\07\11@073705 by Philip Pemberton

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Hi guys,
I'm in the market for a signal generator -- I'm trying to get a PLL to
lock onto an RF (low hundreds of kHz) carrier, then use a phase detector
to decode the ~12.5bps phase-modulated data that's riding on top of the
carrier.

Yes, I'm making a Radio 4 Timecode decoder. Though IIRC the BBC spec
calls it "LF Radio-Data".

Catch: the Hameg signal generator I'm using now doesn't do any form of
modulation besides some quick-and-nasty AM which I've been using to
tweak the filters. 1024-point 12-bit arbitrary waves is about as
advanced as it goes, which isn't going to get me a 198k sine with PM data.

So I'm looking at a new signal generator -- the Agilent 33220A and Tek
AFG3021B are on my shortlist and have basically identical specs (aside
from the Tek's bigger display). I'm leaning towards the 33220 because
it's smaller than the Tek (desk space is at a premium), and it's going
to be tethered to a PC most of the time anyway so the large LCD is
pretty irrelevant. It's also about £200 +VAT cheaper...

Now before I plunk down ~£1k +VAT on one of these boxes... has anyone
actually used one of these boxes? Any comments or criticisms?

Most of what I'll be using it for is <20MHz or so RF testing, bandwidth
tests / frequency response of amplifiers, that sort of thing. I'm also
open to suggestions of similar equipment from other manufacturers...

Thanks,
Phil.

2008\07\11@075859 by Vasile Surducan

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Well, you may get the Agilent at about $400-500 which is good, but if
you need some modulations up to 20Mhz carrier, why don't you consider
a DDS like AD9851 ?
It's definitely cheaper if you have some spare time... and you can
design yourself a quite good signal generator (forget it only if you
need SFDR bigger than 60-70dB and you don't have a good spectrum
analyzer)

Vasile

On 7/11/08, Philip Pemberton <spam_OUTpiclistTakeThisOuTspamphilpem.me.uk> wrote:
{Quote hidden}

>

2008\07\14@163335 by Philip Pemberton

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Vasile Surducan wrote:
> Well, you may get the Agilent at about $400-500 which is good, but if
> you need some modulations up to 20Mhz carrier, why don't you consider
> a DDS like AD9851 ?

No FM or phase modulation...

> It's definitely cheaper if you have some spare time... and you can
> design yourself a quite good signal generator (forget it only if you
> need SFDR bigger than 60-70dB and you don't have a good spectrum
> analyzer)

I am looking into using a couple of the more advanced ADI DDS chips to
generate a QPSK test waveform (and I can probably reprogram that chip to do
BPSK with a +/-22.5-degree shift at 198kHz).. It's a nice idea, but I wanted
to have a go with AM/FM receivers too - and neither the Hameg nor the ADI
chips can do that (easily). AM involves an SA612 multiplier; FM is a lot more
painful, especially with a DDS.

Thanks,
--
Phil.
.....piclistKILLspamspam@spam@philpem.me.uk
http://www.philpem.me.uk/

2008\07\14@165619 by Dave Tweed

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Philip Pemberton wrote:
> Vasile Surducan wrote:
> > Well, you may get the Agilent at about $400-500 which is good, but if
> > you need some modulations up to 20Mhz carrier, why don't you consider
> > a DDS like AD9851 ?
>
> No FM or phase modulation...
>
> > It's definitely cheaper if you have some spare time... and you can
> > design yourself a quite good signal generator (forget it only if you
> > need SFDR bigger than 60-70dB and you don't have a good spectrum
> > analyzer)
>
> I am looking into using a couple of the more advanced ADI DDS chips to
> generate a QPSK test waveform (and I can probably reprogram that chip to
> do BPSK with a +/-22.5-degree shift at 198kHz).. It's a nice idea, but I
> wanted to have a go with AM/FM receivers too - and neither the Hameg nor
> the ADI chips can do that (easily). AM involves an SA612 multiplier; FM
> is a lot more painful, especially with a DDS.

Huh? One of us is very confused.

I thought most DDS chips has frequency and phase offset registers that made
FM and PM dead easy...

Even if your modulating signal is in the analog domain, you just digitize
it with a suitable ADC with a suitable sample rate, and feed it on through
to the DDS. What am I missing?

-- Dave Tweed

2008\07\15@144604 by Sean Breheny

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Dave is correct. ADI makes several DDS ICs which can very easily do
AM, FM, and PM simultaneously. They do AM using a mutiplying DAC which
is referenced off the output of another DAC. Some can also do FSK,
BPSK, and ASK directly (i.e., you configure the chip and then you can
just feed in a serial data stream on one pin and it modulates it).
Some also can automatically do frequency sweeps (i.e., let's say you
need to sweep frequency faster and smoother than you can do via the
control interface - you can program it to sweep linearly from freq A
to freq B over time interval T, and then trigger it and it will
execute it). They can pretty much do any type of signal generation you
want.

I've used the AD9852 with great results.

Sean


On Mon, Jul 14, 2008 at 4:55 PM, Dave Tweed <picspamKILLspamdtweed.com> wrote:
{Quote hidden}

> -

2008\07\15@173236 by Philip Pemberton

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Sean Breheny wrote:
> Dave is correct. ADI makes several DDS ICs which can very easily do
> AM, FM, and PM simultaneously. They do AM using a mutiplying DAC which
> is referenced off the output of another DAC.

Not exactly difficult then...

> Some also can automatically do frequency sweeps (i.e., let's say you
> need to sweep frequency faster and smoother than you can do via the
> control interface - you can program it to sweep linearly from freq A
> to freq B over time interval T, and then trigger it and it will
> execute it). They can pretty much do any type of signal generation you
> want.

Sounds like exactly what I need, only without the multi-£1,000 price tag...

I've just put in an order for a couple of AD9852s, and I've got some other ADI
DDS chips in my box to play with in the meantime.

AM + PSK could be quite handy - test without the modulation to get the PLL
stuff working, then add some audio to the PSK carrier to test the sideband
filter. Finally, add the RF front end and make that work...

Sounds like a plan, and a nice project to boot. It gives me a good reason to
finally learn about L-C filter design too...

Thanks,
--
Phil.
.....piclistKILLspamspam.....philpem.me.uk
http://www.philpem.me.uk/

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