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

RE: CalAmp DownConverter Info-RevA Response



Drew,

Not sure how you could be receiving 2400 at 120. The LO is at 2380 which
would put 2400 at 20 MHz.

I did have the thought of retuning the filter (and yes - combline finger
extensions would get it down)- bypassing the internal IF amp (filtered for
100 to 350 Mhz) - leave the LO alone (at 2380) and convert 2401.2 to 21.2
MHz. BUT - that configuration has serious image problems.

Regarding the input filter. The MMDS folks needed front end filtering to
reduce serious radar interference problems from the 2.7 GHz region. Unless
you have an interference problem around 2.4 GHz you don't need input
filtering. Remember that if you use a high gain antenna at 2.4 GHz - it acts
as a filter off frequency. However, you do need some image filtering at the
LNA output prior to going into the mixer.

BTW, the output of the two stage LNA has a 3 pole interdigital image
rejection filter on the PCB tuned for 2500 to 2690 MHz. Just another
conplication!!!

A question was asked about the "test" port. It is just a coupled down (about
20 dB) version of the IF out signal.

So I still think its best for parts, but good luck to you adventurous ones
out there. After all - that's what Amateur Radio is all about.

Regards...Bill - N6GHz

-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On
Behalf Of Andrew Glasbrenner
Sent: Thursday, June 09, 2005 11:53 AM
To: Bill Ress; amsat-bb@amsat.org
Subject: Re: [amsat-bb] CalAmp DownConverter Info


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 fingers.

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
----
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
----
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



AMSAT Top AMSAT Home