[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: CalAmp DownConverter Info

Drew & Bill,
I can confirm the PTFE tape over the filter (cover all the fingers) does indeed work well (and takes only 5 minutes to install).  I originally saw this mod on WC0Y's site and applied it to several versions of the CalAmps.  It universally worked as Ward described, effectively moving the frequency down to where the 2401 -> 123 MHz conversion region has much improved gain and NF.  I did my testing using a weak signal source and monitoring the output on my receiver (usually an FT-100).  I found these units with the tape applied worked better than a modestly converted Drake, but were not as good as the popular TSI d/c's.
Jerry, K5OE/G
KO4MA said...
Mine seemed to receive pretty well at 2400 but dropped off fast below that. I 
listened to the output on my Kenwood F6A at 120mhz. I know that others have 
retuned the filters on othe cal amps with PTFE tape, or by lengthening the comb 

I guess the real proof will be to just try it when 51 goes back to V/S. I'm 
still guessing they'll work for 51 and SSETI.

Thanks for the information Bill.

73, Drew

-----Original Message-----
From: Bill Ress <bill@hsmicrowave.com>
Sent: Jun 9, 2005 1:24 PM
To: amsat-bb@amsat.org
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!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org