On Dec 30, 8:08*am, M0WYM wrote:
I wonder if anyone knows of a project or kit that uses a 'scope
timebase output as the basis of an HF spectrum analyser. My aim is
to make something that would be useful for filter work so I'm not
necessarily looking for very wide frequency sweep.

TIA,

Charlie.

For filter work, I think you probably want a "sweep generator", not a
"spectrum analyzer". Many of the elements are the same but a sweep
generator is a far less ambitious project that is probably what you
want for alignments and filter design.

Tim N3QE

"Tim Shoppa" wrote in message
...
Charlie.

For filter work, I think you probably want a "sweep generator", not a
"spectrum analyzer". Many of the elements are the same but a sweep
generator is a far less ambitious project that is probably what you
want for alignments and filter design.

Tim N3QE

I would think a good SA with a tracking generator would be
cat's meow. I wonder how a flat noise source would work
in lieu of the TG to plot filter responses on a SA?

In message , Tio Pedro
writes

"Tim Shoppa" wrote in message
...
Charlie.

For filter work, I think you probably want a "sweep generator", not a
"spectrum analyzer". Many of the elements are the same but a sweep
generator is a far less ambitious project that is probably what you
want for alignments and filter design.

Tim N3QE

I would think a good SA with a tracking generator would be
cat's meow. I wonder how a flat noise source would work
in lieu of the TG to plot filter responses on a SA?

A flat noise generator does indeed work well as a wideband signal
source. However, to make sense of the trace, the spectrum analyser needs
a lot of lowpass filtering of the signal (after detection). This is
averages the spiky noise signal. Most modern digital analysers do have
an 'averaging' function but, on the older 'analogue' analysers,
filtering works fine. You would normally the maximum filtering possible
- typically 100 or 30Hz.
--
Ian

M0WYM wrote:

M0WYM wrote:


That is neat but it works out as over £200 here

Just seen an add for it in this months RadCom, Martin Lynch has it
at £259.95 ($426)!


Charlie.

That's a pretty good price, but if you're prepared to import it yourself, you
can save some money. My HP and Avantek SAs cost over £35000 together!

Bob

On Dec 30, 4:39*pm, "Tio Pedro" wrote:
"TimShoppa" wrote in message

...
* Charlie.

For filter work, I think you probably want a "sweep generator", not a
"spectrum analyzer". Many of the elements are the same but a sweep
generator is a far less ambitious project that is probably what you
want for alignments and filter design.

Tim N3QE

I would think a good SA with a tracking generator would be
cat's meow.

Well, yeah, if you can swing it. But a sweep generator is more than
sufficient for filter design and alignments. And every decent radio/TV
repair shop had one already meaning they show up really really cheap
on E-bay or hamfests a lot. Or you can homebrew a sweep generator (see
EMRFD or a ARRL handbook) out of junk box parts for your particular
band of interest.

Tim N3QE

On Dec 30 2008, 8:08 am, M0WYM wrote:
I wonder if anyone knows of a project or kit that uses a 'scope
timebase output as the basis of an HF spectrum analyser. My aim is
to make something that would be useful for filter work so I'm not
necessarily looking for very wide frequency sweep.

TIA,

Charlie.

--
M0WYMwww.radiowymsey.org

Sign today!http://petitions.pm.gov.uk/SaveShortwave/

Hey OM
In the old analog TV days I used a cable ready varactor tuner as a
sweep generator to drive the scope and MAKE it a spectrum analyzer.
All you needed was a ramp voltage to sweep the varactor tuning with.
Nowadays I could use a transceiver hooked up to a computer and use
digipan or ham radio deluxe to do that.

73 OM
n8zu

On Dec 30 2008, 9:41*am, "Tio Pedro" wrote:
"M0WYM" wrote in message

...

I wonder if anyone knows of a project or kit that uses a 'scope timebase
output as the basis of an HF spectrum analyser. My aim is to make something
that would be useful for filter work so I'm not necessarily looking for
very wide frequency sweep.
* Charlie. M0WYM

My own analyzer was a kit for a QST project sold by
A&A Engineering; the design centered around a CATV
module and had it's own timebase and IF strip/log detector
internally. The analyzer used the scope as a X-Y display.
For serious SSB and CW filter work the VCO is going to
be tricky, you'll need low phase noise, etc.; and a good
set of narrow IF filters that can be swept is another
can of worms. *Most of the ham analyzers are better
suited for wider IF responses and wide sweep ranges.
I did a major rework of the IF and Log Amp using an
Analog Devices chip, but the analyzer still has
limitations.

I'd seriously look at some of the DSP receiver kits that
are now on the market--most offer spectrum display
on the computer screen, and adding a good, but
simple, sweep generator might be an easier approach.

Pete

I had a little one band kit radio that was varactor tuned in my hands
for a while and used the sweep voltage from a scope to to drive the
varactors. I was interesting but the scope didnt have enogh
persistence to show a good display. It really looked cool when you
used a marker generator with it in a dark room.

JImmie

JIMMIE wrote:
SNIP

I had a little one band kit radio that was varactor tuned in my hands
for a while and used the sweep voltage from a scope to to drive the
varactors. I was interesting but the scope didnt have enogh
persistence to show a good display. It really looked cool when you
used a marker generator with it in a dark room.

JImmie


Jimmie,

That sounds like fun - I will have to try that with my BITX20A which
I modding to varactor tuning

Charlie.


--
M0WYM
www.radiowymsey.org

Sign today!
http://petitions.pm.gov.uk/SaveShortwave/

Dale Parfitt wrote:


"M0WYM" wrote in message
...
I wonder if anyone knows of a project or kit that uses a 'scope timebase
output as the basis of an HF spectrum analyser. My aim is to make
something that would be useful for filter work so I'm not necessarily
looking for very wide frequency sweep.

TIA,


Charlie.

Hi Charlie,
For very little money, you can buy the miniVNA:
http://www.miniradiosolutions.com/

That will far outplay anything you can build. Because it makes use of a
PC, it will have features well beyond a simple SA + tracking generator. In
addition, it's a vector device.

GL,
Dale W4OP

You could build a N2PK VNA which is pretty accurate.

Chris

On Jan 2, 5:16 am, M0WYM wrote:
JIMMIE wrote:

SNIP



I had a little one band kit radio that was varactor tuned in my hands
for a while and used the sweep voltage from a scope to to drive the
varactors. I was interesting but the scope didnt have enogh
persistence to show a good display. It really looked cool when you
used a marker generator with it in a dark room.

JImmie

Jimmie,

That sounds like fun - I will have to try that with my BITX20A which
I modding to varactor tuning

Charlie.

--
M0WYMwww.radiowymsey.org

Sign today!http://petitions.pm.gov.uk/SaveShortwave/

Hey OM
You'll have to find that sweet spot for the ramp sweep frequency,
depends on the bandwidth of the scope or the persistence of the crt.
The sweep bandwidth depends on the varactor tuning voltage, not on
the frequency. So you have to adjust the peak voltage of the ramp to
adjust the bandwidth. On the scope where X input is your ramp voltage
and Y input is the detected output of the tuner, with the sweep on the
scope turned off. The resolution will depend on the input bandwidth of
the tuner.

73 OM
n8zu