[450] Goshen ham fest

[Vinnie Grosso]

Is anyone thinking of going to Goshen tomorrow for the Ham Fest?

I'm seriously thinking

Vinnie

On 5/17/2010 6:19 PM, John Foege wrote:
> Well, after searching Craigslist this morning, I found a Uniden
> Bearcat 560xlt for $10. I didn't have any specs and I had no clue what
> the block diagram of the receiver looked like. The price was right,
> however, so I picked it up.
>
> Turns out this Bearcat is almost identical in how it operates as, I
> would assume, almost all others. It's a standard 2 stage conversion
> receiver. The first IF is 10.7mhz and the second IF 455khz. The first
> IF stage filter is just a run-of-the-mill 120kc or something wide
> crystal filter. The FM IF demodulator section utilizes an MC3359 IC,
> which incorporates a built-in mixer and FM demodulator and various
> other assorted goodies. The MC3359 has a section for the external
> 455khz IF filter, which in this scanner is a Murata SFR-450D 5-pin
> ceramic lattice filter. It has a 6db bandwidth of +/- 10khz. That's
> pretty standard for a scanner reciever.
>
> The weather satellites are FM modulated and deviate generally +/- 15kc
> around the 137mhz carrier. So a 2nd-stage IF filter BW of 30kc would
> be appropriate, however, one must also take into account the doppler
> shifft of approximately +/- 4.5kc during a pass. Therefore, the
> optimal 2nd IF filter BW is +/-20kc or 40kc total.
>
> Unforunately, it is extremely hard to find a ceramic filter that has
> this much BW. Best I could find was +/-30kc. According to the NOAA's
> manual on constructing a station for APT (Automatic Picture
> Transmission) reception, modified scanners with a 30-40kc 2nd IF
> passband perform well. So, albeit 10kc low and sub-optimal, the 30kc
> bandwidth on my modified bearcat will produce much better pictures
> than the original 20kc. It is, after all, a 50% increase in bandwidth.
>
> The only thing to do now is homebrew a quadrafiliar helix antenna for
> the 137mhz band and scrap together a simple mast mount preamp for said
> QFH antenna to make up for the less-than-spectacular sensitivity of
> your typical scanner front-end.
>
> Any comments? Suggestions? Anyone interested in the results or want me
> to take some pics and document it? It's a pretty cool little project
> for $15.
>
> Scanner $10
> New Ceramic filter $5
>
> $15 is way better than $250++ for a new Weather Sat receiver from
> various vendors brand new, and it should work just as well!
>
> John
> KB1FSX
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>
>    

-- 
Vinnie Grosso
Vinnie at Vinnievision.com
Office 917-546-6661
Cell 917-697-6229
Fax 212-501-7955
Skype/Twitter: Vinnievision

Let's do work worth doing !!
Megan Blewett

The Best Way to predict the Future, is to invent it !!
Peter Drucker

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