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Re: CalAmp DownConverter Info



Hi Roger,

I was wondering if you have any recommended web pages describing how to use 
brass shims and teflon tape to rework comb filters.
I too bought one of these units, and am now watching the bb and hoping to 
glean some tech info on it.

73s
Robin
KE7ARL


----- Original Message ----- 
From: "Rogerkola" <Rogerkola@aol.com>
To: "Bill Ress" <bill@hsmicrowave.com>; <amsat-bb@amsat.org>
Sent: Thursday, June 09, 2005 11:33 AM
Subject: Re: [amsat-bb] 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.
>> Not an AMSAT member? Join now to support the amateur satellite program!
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> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
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