[Premium-Rx] Racal IF Converter question

[Thomas Adams]

Yeah, that's what I'd think too...   1400 KHz and 1000 KHz doesn't 
give a 100 KHz output!

I'm not sure exactly WHAT Racal is doing inside of this MS-561/2 box 
to pull that one off, thus part
of the need for a schematic! The curiosity is killing me!

I'm just hoping that somebody here has some experience with the 
MS-561/2 and can tell me if the two
IF conversion boards in it are identical, and can produce suitable 
outputs for driving an MA-168.


Mr. T., W9LBB




At 06:29 PM 1/31/2009, FRANCIS CARCIA wrote:
>sounds like all you need is a 1500 KHz oscillator driving 2 double 
>balanced mixers. 1400 of each IF into the RF ports and 1500 khz into 
>LO ports. The two IF ports make 100 KHz and 2900 KHz so all you need 
>is a 2 low pass filters to end up with 2- 100 kHz signals.
>
>--- On Sat, 1/31/09, Thomas Adams <quixote2 at ix.netcom.com> wrote:
>From: Thomas Adams <quixote2 at ix.netcom.com>
>Subject: [Premium-Rx] Racal IF Converter question
>To: premium-rx at mailman.qth.net
>Date: Saturday, January 31, 2009, 7:14 AM
>
>Greetings!
>
>I've been looking at a project that's been on the back burner for a 
>while; setting up a pair of Racal RA-1772
>receivers for diversity operation with a Racal MA-168 Diversity 
>Combiner Switch.
>
>Currently, I'm doing polarization diversity that's based on 
>demodulated audio of RTTY, using the audio switching
>built into the Universal M-7000 and M-8000 digital decoder boxes.
>
>I think the MA-168 can do better. It takes IF signals from both 
>receivers and bases it's choices on the IF signal
>voltage, instead of on the demodulated audio.  The MA-168 then 
>demodulates the IF signal and essentially combines
>the receiver outputs into a single line level audio channel. That 
>would work a lot better for me, because I want to
>insert an outboard DSP box in front of the digital decoder boxes.
>
>All well and good, but there's a fly in the ointment...  the MA-168 
>takes an IF input frequency of 100 KHz, and the
>last IF of the RA-1772 is 1400 KHz.
>
>Apparently somebody else along the line encountered this same 
>problem, because Racal produced an external add-on
>for the RA-1700 series rigs, the MS-561/2. It appears to take two 
>channels of 1400 KHz IF and a 1000 KHz oscillator
>input (from the RA-1772's synthesizer) , and spits out two channels 
>of 100 KHz IF signal.
>
>Here comes the question...
>
>The MS-561/2 was apparently intended for a purpose other than 
>diversity setups; the IF inputs are marked for the main
>IF output, and the ISB option output from the receiver. It was 
>clearly intended to deal with two outputs from ONE receiver,
>not converting the IF frequencies of TWO receivers.
>
>I can't find a schematic or specs of any sort on the MS-561/2, and 
>there's no mention of it in the RA-1772 manuals.
>
>Are the two converter channels of the MS-561/2 identical, so that 
>the box can be used for diversity setups without any
>changes?
>
>Thanks,
>
>Tom, W9LBB
>
>
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