EMRFD Message Archive 2158

Message Date From Subject
2158 2008-10-01 19:25:46 rcbuckiii Crystal Filter Sweeper
I am building a general coverage 2-30 MHz receiver. I have an AD9951
DDS and an AD831 mixer built and working. I also have the Hycas IF
amplifier and S-meter circuit partially assembled. I will finish it
when the last parts arrive in a couple of days.

I want to get the receiver running before I address the crystal
filters. I plan on using a 48 MHz 1st IF and a 9 MHz 2nd IF. I want
the 48 MHz crystal filter to be 7-10 MHz wide so it will pass SWL AM
broadcast stations. The 9 MHz IF will have 3 crystal filters for AM,
SSB, and CW.

My question is about the 48 MHz filter using 3rd overtone crystals. I
think the only way to build it is to get close with an initial design
and then tweak it by sweeping it. I don't think the C and Lm
measurements at the fudamental frequency will be close enough at the
overtone frequency.

I have done a lot of reading about crystal filter design techniques
and have seen several articles on "poor man" sweepers. I wonder what
experience others have had with these. And is any one design better
than another? I have an old 20 MHz dual trace scope that I would use
for display purposes. The sweep would have to be constant so the
effects of adjustment would be seen in real time.

I have all the parts for Wes's spectrum analyzer but haven't built it
yet. I have built the 250 MHz Network Analyzer described in the March
2002 QEX magazine. However it does not display in real time. I mainly
use it for signal generation purposes since it is accurate to 1 Hz.

I also thought about just writing code to have my AD9951 DDS sweep
about +/-5 KHz either side of 48 MHz in 1 or 5 Hz steps. I could also
use a spare pin on the microcontroller to control the horizontal
pulse to the scope.

Any suggestions/experiences would be appreciated.

Thanks.

Ray
AB7HE
2159 2008-10-01 21:09:53 brainerd@wildblue... Re: Crystal Filter Sweeper
Ray:
If you are looking for something to sweep a filter, then use your 9951 going to the filter
followed by something like an AD8307 or an AD8310. If you follow that with an A/D going in
to the computer, you can store the frequency and response and plot the response on the
computer(this is a scalar network analyzer). Note that my 995x board is designed to do just
this. It has an AD995x, an AD8310, and a PIC with A/D inputs and a USB interface. The
hardware is there, the firmware and PC software needs to be written.

Dave - WB6DHW
<http://wb6dhw.com>


On 2 Oct 2008 at 2:14, rcbuckiii wrote:

> I am building a general coverage 2-30 MHz receiver. I have an AD9951
> DDS and an AD831 mixer built and working. I also have the Hycas IF
> amplifier and S-meter circuit partially assembled. I will finish it
> when the last parts arrive in a couple of days.
>
> I want to get the receiver running before I address the crystal
> filters. I plan on using a 48 MHz 1st IF and a 9 MHz 2nd IF. I want
> the 48 MHz crystal filter to be 7-10 MHz wide so it will pass SWL AM
> broadcast stations. The 9 MHz IF will have 3 crystal filters for AM,
> SSB, and CW.
>
> My question is about the 48 MHz filter using 3rd overtone crystals. I
> think the only way to build it is to get close with an initial design
> and then tweak it by sweeping it. I don't think the C and Lm
> measurements at the fudamental frequency will be close enough at the
> overtone frequency.
>
> I have done a lot of reading about crystal filter design techniques
> and have seen several articles on "poor man" sweepers. I wonder what
> experience others have had with these. And is any one design better
> than another? I have an old 20 MHz dual trace scope that I would use
> for display purposes. The sweep would have to be constant so the
> effects of adjustment would be seen in real time.
>
> I have all the parts for Wes's spectrum analyzer but haven't built it
> yet. I have built the 250 MHz Network Analyzer described in the March
> 2002 QEX magazine. However it does not display in real time. I mainly
> use it for signal generation purposes since it is accurate to 1 Hz.
>
> I also thought about just writing code to have my AD9951 DDS sweep
> about +/-5 KHz either side of 48 MHz in 1 or 5 Hz steps. I could also
> use a spare pin on the microcontroller to control the horizontal
> pulse to the scope.
>
> Any suggestions/experiences would be appreciated.
>
> Thanks.
>
> Ray
> AB7HE


Dave - WB6DHW
<http://wb6dhw.com>
2160 2008-10-02 08:38:19 wimmie262000 Re: Crystal Filter Sweeper
2161 2008-10-02 08:38:27 timshoppa Re: Crystal Filter Sweeper
2162 2008-10-02 16:13:33 timshoppa Re: Crystal Filter Sweeper
2163 2008-10-02 20:43:47 rcbuckiii Re: Crystal Filter Sweeper
2164 2008-10-02 20:43:47 bobtbobbo Re: Crystal Filter Sweeper
2165 2008-10-02 20:54:48 jr_dakota Re: Crystal Filter Sweeper
Here ya go, just what the doctor ordered

http://www.qsl.net/om3cph/om3cph.html

I haven't built the hardware up yet myself but I have all the parts
for the original version http://www.qsl.net/om3cph/om3cph.html

Here's a more advanced versi
2170 2008-10-03 09:29:20 rcbuckiii Re: Crystal Filter Sweeper
JR,

Thanks. That is very similar to something I was considering. It
appears to do constant updates which would give the appearance
of "real time".

Ray AB7HE


2172 2008-10-03 12:40:26 wimmie262000 Re: Crystal Filter Sweeper
2178 2008-10-03 21:56:56 rcbuckiii Re: Crystal Filter Sweeper
2180 2008-10-04 01:41:58 wimmie262000 Re: Crystal Filter Sweeper