Hi Ashar:
The Specan is something I can build with my limited resources, I am a
newbie when comes to using the arduino IDE, case in point I am still having
problems trying to compile the sweeperino sketch , was wondering where the
si5351 comes into play even though you are using the Si570. I want get the
sweeperino built but until I get past this hurdle the project is stalled.
Any help is greatly appreciated, as a side note I built a BITX20 still use
it once in a while fun project.
73 Ross Bell K7RSB
On Fri, Aug 28, 2015 at 6:45 AM, Joe Rocci <joe@xxxxxxxxxx> wrote:
Yes, the sampling rate would have to be slow to accommodate detecting the
low frequencies involved in a narrow resolution bandwidth. We actually had
a 300 khz BW post-detection LPF and the requirement wasn’t for fast
real-time refresh. It was a remote monitor unit on a broadband network that
characterized a 5-200 mhz spectrum, plotting the spectrum on a remote
display in a Network Operations Center (NOC). It worked well for its
purpose. I I think it might be all that many hams might need, given the
minimal complexity. Clearly, it’s not going to replace a high quality (read
“High Priced”) lab instrument, but it’s much more than just a “curiosity”.
Also, your idea of a DSP back-end could help, but I think you’d have to
deal with the issue of images in the DC detection process resulting in 2
responses, whereas the envelope measurement approach merely folds the image
in as half of the resolution BW. However, if the “mixer” were a
Tayloe-style QSD, you might fix that problem too.
Joe
*From:* Ashhar Farhan <farhanbox@xxxxxxxxx>
*Sent:* Friday, August 28, 2015 9:34 AM
*To:* minima@xxxxxxxxxxxxx
*Subject:* [minima] Re: A homebrew spectrum analyzer
joe,
at audio frequencies, we could just rely on a sound card to read 16-bit
audio and convert it to 70 or 80 db scale. i have tried this approach.
upconvert to 100 Mhz and run a product detector at 100 MHz. the trouble is
the sampling rate is quite slow.
let me illustrate the problem : to scan 0-60 MHz, given 20 Khz sampling
bandwidth, we will need 60,000/20 = 3000 data points. each datapoint would
take about 10 msec. the entire sweep would take 30 seconds.
however, the great achievement could be if we ran dsp inside the audio
bandwidth too and thus, provided a variable resolution bandwidth in
software.
- f
On Fri, Aug 28, 2015 at 6:55 PM, Joe Rocci <joe@xxxxxxxxxx> wrote:
A real minimalist might build a spectrum analyzer out of a direct
conversion receiver architecture. The resolution bandwidth turns out to be
twice the output audio bandwidth, making it easy to obtain variable
resolution bandwidth. The major obstacle is that the DBM has an inherent
response at the 3rd harmonic of the LO only about 15 db down. I actually
designed a product based on this approach many years ago. I cured the 3rd
harmonic problem with a bank of 4 switched lowpass filters in the
front-end.
Worked very nicely. We sampled the “audio” response with an 8-bit A-D,
which limited our dynamic range to about 40 dB. Using an AD8307 at the
output would vastly improve this.
Joe
W3JDR
*From:* Ashhar Farhan <farhanbox@xxxxxxxxx>
*Sent:* Friday, August 28, 2015 8:34 AM
*To:* minima@xxxxxxxxxxxxx
*Subject:* [minima] Re: A homebrew spectrum analyzer
thanks all. you will understand that this is a reprise of the original by
wes and terry. the two papers written by them are linked in my article. do
give it a read.
- f
On Fri, Aug 28, 2015 at 5:23 PM, Biagio Pepe <blaispe@xxxxxxxxx> wrote:
Fantastic Job Fahran !!! Really a brilliant work
Simply Love it
73's
2015-08-28 7:01 GMT+02:00 Ashhar Farhan <farhanbox@xxxxxxxxx>:
While working on the Minima project, I needed a spectrum analyzer to
measure the performance. The new specan is as complicated as a simple SSB
rig, probably even simpler.
This is an Si570/Arduino controlled spectrum analyzer that can be built
for less than hundred dollars. It is simple to build and it can be used to
measure IMDR, spurs, harmonics, etc. It doesn't need an oscilloscope.
I like you all to read about it
http://hfsignals.blogspot.in/p/specan-reboot-of-w7zoi.html
- f
