"A" wrote in message
.com...
At this point I'd like to know what your problem is with "significant amount
of energy..." compared to whatever your ultimate goal is.

I'll get something in the ballpark of an -90dBm spur at the IF when the noise
floor is down around, say, -120dBm. Hence I have a harder time recovering
signals at, say, -100dBm even though they still have a decent SNR (and my
commercial receives have no difficulty at all hearing them). This is measured
on an Agilent 8563 spectrum analyzer.

Could your PLL synthesizer be dirtier than you think?

I've done some wideband sweeps of it, and there are some spurs that are only
~ -70dBc. It's obvious when you choose a channel that suffers from these
higher-level spurs, though... it'll add 20dB or more to the IF spur. I
ditched my homebrew PLL-based synthesizer for a good HP box borrowed for
testing, though (its spurs are more like -90dBc worst case), and the problem
is still there.

One way I would think about this is to ask if you looked at known circuits
that work and ask yourself what are you doing that is different from known
circuits that work.

The usual problem is that very few circuits found on the Internet actually
come with performance data -- unless you build them yourself, you really have
no way to know if they're just as bad or worse than your own efforts!

We also had some posts maybe 1-2 years ago where a guy was working with
chips and circuits and computer modelling (IIRC) and he was unhappy that he
was not getting (with real circuits) what his computer modeling program told
him he was supposed to get.

It would almost be alarming if those circuits did work, in real life, within,
say, 0.1dB of their simulated results rather than the more typical 1-5dB
that's often still considered "good agreement!"

---Joel

See at end...

On Wed, 11 Jun 2008, Joel Koltner wrote:

"A" wrote in message
.com...
At this point I'd like to know what your problem is with "significant amount
of energy..." compared to whatever your ultimate goal is.

I'll get something in the ballpark of an -90dBm spur at the IF when the noise
floor is down around, say, -120dBm. Hence I have a harder time recovering
signals at, say, -100dBm even though they still have a decent SNR (and my
commercial receives have no difficulty at all hearing them). This is measured
on an Agilent 8563 spectrum analyzer.

Could your PLL synthesizer be dirtier than you think?

I've done some wideband sweeps of it, and there are some spurs that are only
~ -70dBc. It's obvious when you choose a channel that suffers from these
higher-level spurs, though... it'll add 20dB or more to the IF spur. I
ditched my homebrew PLL-based synthesizer for a good HP box borrowed for
testing, though (its spurs are more like -90dBc worst case), and the problem
is still there.

One way I would think about this is to ask if you looked at known circuits
that work and ask yourself what are you doing that is different from known
circuits that work.

The usual problem is that very few circuits found on the Internet actually
come with performance data -- unless you build them yourself, you really have
no way to know if they're just as bad or worse than your own efforts!

We also had some posts maybe 1-2 years ago where a guy was working with
chips and circuits and computer modelling (IIRC) and he was unhappy that he
was not getting (with real circuits) what his computer modeling program told
him he was supposed to get.

It would almost be alarming if those circuits did work, in real life, within,
say, 0.1dB of their simulated results rather than the more typical 1-5dB
that's often still considered "good agreement!"

I don't recall what the guy was upset about. I don't think (IIRC) that we
had any comments regarding what, quantitatively, he was looking for vs.
what he was getting, quantitatively, but he was definitely upset.

I don't have anything like the fancy gear you have and my criteria are
more or less "if you can hear it and its OK with you, then its fine" (for
receivers anyway). On transmit, I have enough tuned circuits in various
places that my spurious signals should be good enough for the FCC. And,
I'm using quite clean free running oscillators at VFO, LO points. Its
really wonderful to be able to see sine waves on any one of my three
Tektronixs scopes, thought. I'll add that if I don't have at least some
minimum number of tuned circuits, that "sine wave" develops very visible
"distortions." Maybe someday I'll be interested in quantitating them.

In the meantime, good luck on your endeavors. And, thanks for the fills on
the technical stuff. Can't help you any more than that.

---Joel

"A" wrote in message
.com...
I don't have anything like the fancy gear you have and my criteria are more
or less "if you can hear it and its OK with you, then its fine" (for
receivers anyway).

I'm in a very fortuitous position, being somewhat a novice at RF design
personally, but working at a company that's been doing it for years so I have
access to a fair amount of nice test equipment. :-) Sometimes it's a little
weird, though -- until a couple of years ago now we had network analyzers
going to 6GHz but no scope better than 100MHz!

I think projects like the TAPR VNA (http://www.tapr.org/kits_vna.html -- now
sold by Ten-Tec) are great, although it's unfortunate that it tops out at
100MHz, as in many cases one can "get by" with a lot less down at HF or even
2m than those trying to homebrew 70cm or higher gear. Even getting, say, 1GHz
spectrum analyzers with tracking generators is not at all cheap (meaning,
within most hobbyist's budgets, which I'd say is something $1k or less for
such a device) -- there's been discussion on and off for ages on how such a
tool would sell like hotcakes, given how much it would benefit homebrewers and
commercial users. I kick around the idea of trying to build something like
that myself, but I do already have enough experience to know that there's a
very large investment in time between "design looks good on paper" and "design
actually works" if you're shooting for decent dynamic ranges and resolution
bandwidths.

Thanks for your input,
---Joel