[Collins] Questions about the Collins 18S and 618* equipment

[Dr. Gerald N. Johnson]

On Mon, 2009-04-20 at 11:10 -1000, Michael Tauson wrote:
> The 18S-* and 618* equipment has been on my mind a lot of late.  This
> isn’t the first time they have fallen under my curious eye but it has
> lead to some questions about them.
> 
> I have an 18S-4 but lack a schematic and information on the coils &
> output network to move it into the ham bands.  (None of the crystals
> that came with it were even close.)  If anyone has this information
> and would be willing to share (plus any tune up hints), I would be
> grateful.

I don't have those details either. Perhaps CCA has some of them.

With plug in crystals and coils, one way to get LSB is to select a
crystal on the opposite side of the injection as used to get USB.

In some of the rigs, a USB filter is used, and it at least conceptually
its possible to add filter switching to allow using both a USB and a LSB
filter for the same carrier frequency while preserving the frequency
calibration. Otherwise, at a loss of frequency calibration, its
practical to shift the BFO to the other side of the filter passband. In
S-line that's how its done, with the addition of a frequency shifter in
the PTO to shift it in the opposite direction so the dial stays the same
for the same carrier frequency.
> 
> Next, is the 618M-1 the same as a 618S-1/MC?  If not, what is it?
> 
> What (if any) modules are interchangeable between the 618S-1 &
> RT-311/ARC-38, the 618S-1/MC & RT-594/ARC-38S and between the two
> groups?  Also, does anyone know of a way to make the SSB versions
> operate on LSB?
> 
> The same question exists between the various versions of the 618T and
> the military versions thereof.  Also, was there any restrictions on
> the sets that wouldn’t allow them to operate in CW or data mode or was
> that simply a function of the control head?
> 
> And finally, is there any way to make the 618S and 618T series
> equipment able to tune between the 1 KCs divisions (like the
> RT-662/GRC-106) or is that a near impossible can of worms?

When the rig is based on a digital synthesizer, its hard with the
existing logic to split the 1 KHz reference. But if there is an offset
oscillator because of slow logic, its possible to do fine tuning by
warping that offset oscillator, or to warp the synthesizer reference to
get fine tuning. Today, one can get a single chip synthesizer that will
do fractional N ratios to get arbitrarily fine steps while keeping a
coarser reference frequency.

And then there's direct digital synthesis techniques that create signals
at an arbitrary frequency with a couple chips in a package. There's some
discussion at: http://softrocksdr.wikispaces.com/

Possibly a ham vendor like AADE has a general purpose DDS or synthesizer
that could replace the limited capability of the original synthesizer.
At the cost of an external dial or control, unhooking a cable or two
inside the radio, and possibly having to compute frequency different
than the synthesizer display.
> 
> Thank you.
> 
> Best regards,
> 
> Michael, WH7HG

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer