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Re: CalAmp DownConverter Info



Hi Bill...

Just some ideas reguarding your points:

> The biggest problem is the 7 pole combline filter right at the input
> covering 2.5 to 2.7 GHz. Tuning it down to 2.4 GHz proved unsatisfactory
> since the tuning screws were already almost touching the resonators.

In the past the comb filters have been lengthened with brass shim stock or 
capacitivly lowered with teflon tape...could this work here?

>To convert the unit to 2401 would require removing (by-passing) the input
>filter, some slight input amplifier matching circuit tweaking, and 
>conversion of the LO to 2257 Mhz.

Would this be necessary if the original IF of 123 MHZ is retained with the 
proper receiver?

>100 to 350 MHz IF amplifier which has both high pass
> and low pass filter elements for the IF band.

Did you have a chance to measure the cutoff characteristics of the high pass 
filter to see if it would pass 121 Mhz without loss? Possibly the high pass 
filter could be bypassed?

I guess the bottom line would be to measure the gain and noise figure in 
it's current form and to decide if it was worth a conversion.....

Just my thoughts outloud...

Roger
WA1KAT



----- Original Message ----- 
From: "Bill Ress" <bill@hsmicrowave.com>
To: <amsat-bb@amsat.org>
Sent: Thursday, June 09, 2005 1:24 PM
Subject: [amsat-bb] CalAmp DownConverter Info


> Since the responses to my post indicated that I should post this response
> for all - here's what I have...
>
> The unit is for the MMDS/ITFS band which is 2500 to 2690 MHz. This is the
> instructional TV band also used by some wireless pay TV services.
>
> I purchased the unit for parts: connectors, IC's, transistors, a great
> weather protected cast housing, etc., knowing that conversion would be
> questionable and I think you'll agree.
>
> The biggest problem is the 7 pole combline filter right at the input
> covering 2.5 to 2.7 GHz. Tuning it down to 2.4 GHz proved unsatisfactory
> since the tuning screws were already almost touching the resonators.
>
> The LNA uses a device yet to be identified followed by a R37 (believed 
> this
> is a NEC device).
>
> The mixer uses a pair of Schottky diodes (smd = C2) and a 3 dB branch line
> coupler. This circuit is typically somewhat broadband and should work at
> 2401 MHz.
>
> This is followed by a 100 to 350 MHz IF amplifier which has both high pass
> and low pass filter elements for the IF band.
>
> The unit is internally down regulated to 12 volts. Power is applied via a
> bias tee to the type "f" 75 ohm output connector. While the type "f"
> connector and output circuit has been designed for 75 ohms, driving 50 
> ohms
> is no problem.
>
> The LO is a crystal controlled PLL using a 2380 MHz VCO divided by 256 by 
> a
> Fujitsu MB506 (divide by 256) and locked to a crystal at 9.29687 MHz.
>
> To convert the unit to 2401 would require removing (by-passing) the input
> filter, some slight input amplifier matching circuit tweaking, and
> conversion of the LO to 2257 Mhz. This, in my opinion, could only be done 
> by
> one having the expertise and test equipment. Looking at the 2380 MHz VCO,
> I'm sure it could be pulled down to 2257, but again the right equipment 
> and
> knowledge is needed.
>
> But I'm happy with the purchase (I got 2) since the N connectors alone are
> worth the price.
>
> If I can answer any other questions - email me.
>
> Regards...Bill - N6GHz
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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----
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