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'[EE] TV Tuner Based Spectrum Analyzer'
2012\05\24@151325 by Herbert Graf

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Hello all,

well, after a long delay, I've been able to dedicate a little time to my
idle project: a home built spectrum analyzer based on a TV tuner front
end.

I've found what I believe the perfect tuner for me (mostly because it's
something I have in my hands):

http://www.datasheetarchive.com/indexdl/Datasheet-028/DSA00488547.pdf

It's a Temic 4036 RF front end module. I found it on a WinTV PC TV tuner
PCI card.
It's a I2C based tuner, with single 5V power supply (has an onboard
DC-DC to get the 33V needed by the tuner). I stuck the card in a PC,
booted Ubuntu, attached a protocol analyzer (thank you beta version of
the BitScope software, was a major time saver!) on the I2C pins, started
TVTime and changed channels. The module is being programmed exactly as
the datasheet says it should be!

So, with that out of the way, what would be my next step?

First off, the module outputs CVBS (at baseband), and something labelled
IF2 (at 45.75 MHZ). Obviously I need an RSSI circuit. But do I first
have to "tune" the output somehow?
What I'm envisioning (and note, I no NOTHING about RF stuff, so this is
very much a learning project for me) is using a second tuner (some sort
of home built one chip thing with RSSI output perhaps?) that "tunes"
somewhere in the CVBS output with a bandwidth of say 10kHz? So basically
sweeping would be two steps, set the TV tuner to a channel, then sweep
the second tuner across the ~4MHz bandwidth of the CVBS or IF output.
Then step the TV tuner to the next range, and sweep the CVBS or IF
output. Combined I could get everything I need.

Does this sound at all reasonable or am I WAY out of wack here?

Should use the CVBS or the IF output?

Anybody have chip recommendations for how I might build the second
tuner, one hopefully with an RSSI output?

Is there a simpler way to what I'm after? What kind of resolution should
I aim for?

Thanks for any pointers!

TTYL

2012\05\24@174857 by Dwayne Reid

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Have you checked out the "Poor Man's Spectrum Analyzer" at <http://www.science-workshop.com/> ?  They may have circuit blocks that are useful for you.

Searching out "poor mans spectrum analyzer" yields lots of hits - some of those may also be useful.

dwayne


At 01:15 PM 5/24/2012, Herbert Graf wrote:
{Quote hidden}

2012\05\24@233824 by Herbert Graf

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I have seen that before. That site seems to just offer for purchase the details, or parts.

I will have a look to see what kind of hits "poor mans spectrum analyzer" gets me. Thanks for the pointer.

TTYL


On 2012-05-24, at 5:48 PM, Dwayne Reid wrote:

{Quote hidden}

>> -

2012\05\25@090830 by Joe McCauley

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A bit removed from what the OP wanted, but.... This was not designed as a spectrum analyser, but you can get a nice spectrum between 45MHz & 870MHz. Takes 45 seconds to get a full range spectrum though!

http://www.e-callisto.org/

We use them for solar monitoring at http://www.rosseobservatory.ie. I tried to attach 2 spectra, but the list would not let them pass. If anyone wants to see, I can send directly to them as an attachment.

One of these shows frequencies below 45MHz, an up converter was used for this part.

Another option might be http://www.funcubedongle.com/. I've not used one (its on my long list of cool things to try) so I don't know if spectrum analyser type output is possible.

Joe


{Original Message removed}

2012\05\25@104015 by Sean Breheny

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For what it's worth, I think that you are basically on the right
track, Herbert. Good Tektronix or HP spectrum analyzers have
resolution bandwidths down to at least 1kHz and many go down to 100Hz
or even 10Hz (or even lower but that is almost always done in
post-processing by digitizing and then doing an FFT on each block of
samples).

You will see the terms "resolution bandwidth (RBW)" and "video
bandwidth (VBW)". Then there is also averaging or peak detection on
top of this. The distinction is as follows: RBW is the bandwidth of
the RF chain before the detector (power measurement device). VBW is
the bandwidth of the signal chain after the detector. Averaging or
peak detection then refer to how the digital storage portion of the
device records samples - it takes several samples per time step and
saves only one sample and it can save either the average of the
samples or the highest one.

The RBW determines the RF noise floor and also how close two signals
can be and still be resolved by the analyzer into two separate peaks.

The VBW determines how finely the analyzer can discriminate between
two different power levels. This is because a narrower VBW removes
noise in the detector output.

I believe that the averaging/peak detection is somewhat redundant with
the VBW - in other words, they roughly have the same kind of effect on
the signal as decreasing or increasing the VBW, except that the
analyzer often allows you to average signals below some power level
and peak-detect those above that same threshold, whereas VBW is fixed
for an entire scan.

On Thu, May 24, 2012 at 11:38 PM, Herbert Graf <spam_OUThkgrafTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

>>> --

2012\05\27@055503 by cdb

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Of not much help (because I can't find mycopy), Electronics Australia (defunct) did a Spectrum Analyser project based on a TV tuner, I can't recall how the sweep component worked. I vaguely recall an early Elektor magazine (70's or 80's) also did one.

Colin
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2012\05\27@055845 by cdb
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Found this webpage: http://www.nitehawk.com/rasmit/sa50.html

Colin
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cdb, colinspamKILLspambtech-online.co.uk on 27/05/2012
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2012\05\28@131922 by Herbert Graf

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Wow, that would be awesome! Might someone here have a copy of one of
these projects they could scan and send to me?

Thanks! TTYL

On Sun, 2012-05-27 at 19:54 +1000, cdb wrote:
{Quote hidden}

>

2012\05\30@232308 by Eoin Ross

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>From what I recall of a kit using a tuner unit out of a vcr, the was a VCO that did the tuning, and a RSSI voltage out.

A sawtooth was fed to the VCO input, and X input of a scope. The RSSI was fed to the Y input of the scope.

This was a kit available from Dick Smith Electronics New Zealand in the late 90's

Herbert Graf <EraseMEhkgrafspam_OUTspamTakeThisOuTgmail.com> wrote:


Wow, that would be awesome! Might someone here have a copy of one of
these projects they could scan and send to me?

Thanks! TTYL

On Sun, 2012-05-27 at 19:54 +1000, cdb wrote:
{Quote hidden}

2012\05\31@012803 by Manu Abraham

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On Thu, May 31, 2012 at 8:51 AM, Eoin Ross <@spam@ERossKILLspamspamchemstation.com> wrote:
> >From what I recall of a kit using a tuner unit out of a vcr, the was a VCO that did the tuning, and a RSSI voltage out.
>
> A sawtooth was fed to the VCO input, and X input of a scope. The RSSI was fed to the Y input of the scope.
>
> This was a kit available from Dick Smith Electronics New Zealand in the late 90's

Long gone are those PLL based tuners, these days what you get are
these Silcon tuners
which are a bit more slightly complex ones which uses NCO's
(Numerically controlled
Oscillators), Instead of a vanilla VCO. Not a very big deal though,
just some slight topology
differences.

In such a case, you can't feed a sawtooth directly to the
PLL/MOPLL/Silicon Tuner.
You would be very lucky, if you find a really old Tin can tuner which
uses a varactor

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