"larry" ) writes:
Does anyone know where I can find the block diagram of the icom 22s.. I have
the schematic, now I would like the block diagram....to help me understand
the schematic....
Thanks de
Larry ve3fxq


But wouldn't making your own block diagram help you to understand the
schematic?

I'd imagine it's a fairly straightforward receiver, with a stage or
two of amplification going into a mixer that, given the vintage, is likely
a MOSFET. Then right into a 10.7MHz Filter. Then you get
amplification/limiter and the detector, unless, again as I'd suspect, it's
double conversion in which case there'd be just a bit of amplification at
10.7MHz and a second mixer dropping the signal to 455KHz where there'd
be a 455KHz ceramic filter and amplification/limiter and the detector.
You can find that second mixer by looking for a 10.245MHz crystal, though
it might be highside injection with an 11.155MHz crystal. The detector
feeds the audio stages.

The filter(s) will help to define the schematic, as will that second
conversion oscillator if there is a second conversion.

The first mixer will get its signal from the PLL synthesizer. There will
be a VCO that feeds that mixer, though there's bound to be a stage or
two of buffer/amplification between the two stages. One of those
stages may even be a multiplier; I can't remember whether the PLL generates
the actual injection frequency or a submultiple. Memory says the actual
signal from the VFO is fed into a mixer, with a crystal oscillator feeding
its other input, which drops the VCO signal to a low enough frequency that
the programmable divider chain can deal with it. I seem to recall the actual
synthesizer may be mostly in a big IC, with the programmable divider and
phase detector and likely reference frequency and its divider chain in one
package. You can find out by tracing from the diode matrix that programs
the actual channels to wherever it goes.

I don't have a clue of the layout of the transmitter. I don't know
whether offset is added to the matrix data to get the VCO to switch
to the needed frequency on transmit (it can't be on the same frequency
as the receiver injection frequency because that is off the channel
by 10.7MHz, and then more for repeater offsets), or if there is a mixer
in the transmitter chain that adds one of a number of crystal oscillator
frequencies to provide the needed offset. I doubt they generated
the transmitter frequency at a very low frequency like 6MHz and multiplied
up, as was the case with old crystal controlled 2M rigs. But there might
be a doubler or something, running the VCO at half the needed frequency.
Once the signal is on the actual 2M signal, then it's just a matter of
stages of amplification to get it up to the needed level.

Michael