Taking my cue from bandswitching in other designs,
and being motivated by the catacomb in the HRO
NC100X, I wonder if any have encountered bandswitching
by cam driven microswitches?

I presume that the contacts in microswitches must be
similar to those in small relays, and, being mechanical,
would not be subject to electrical failure.

What I envisage is that the most HF coils would be
mormally switched in by the microswitch closest
to the tuning cap, and then when the big cam (Big K? :-) )
slides along to activate that microswitch, the
next lower frequency coil takes over, and so on
and so forth.

Having had one failure by dropping the catacomb
mechanism on one corner, I'm sort of losing heart
at the prospect of making up 50 sliding contacts.

On 11/07/17 11:50, Gareth's Downstairs Computer wrote:
Taking my cue from bandswitching in other designs,
and being motivated by the catacomb in the HRO
NC100X, I wonder if any have encountered bandswitching
by cam driven microswitches?

I presume that the contacts in microswitches must be
similar to those in small relays, and, being mechanical,
would not be subject to electrical failure.

What I envisage is that the most HF coils would be
mormally switched in by the microswitch closest
to the tuning cap, and then when the big cam (Big K? :-) )
slides along to activate that microswitch, the
next lower frequency coil takes over, and so on
and so forth.

Having had one failure by dropping the catacomb
mechanism on one corner, I'm sort of losing heart
at the prospect of making up 50 sliding contacts.

Learn from history. In the days of dual standard TVs (in the UK), some
makers had a large slide switch in the circuit board (this was the era
when even valve sets used PCBs with valve (tube) holders mounted on
PCBs. The switches were often operated by a bowden cable connected to
the VHF turret tuner. The switches had a huge number of contacts and
were infamous for failing- generally getting muck and gunge on them or
the contacts deforming. These were professionally produced items.

Using a similar approach with homemade contacts would seem doomed to
repeat a poor design concept. Learn from the errors of others.

On Tue, 11 Jul 2017 12:24:34 +0100, Brian Reay wrote:

On 11/07/17 11:50, Gareth's Downstairs Computer wrote:
Taking my cue from bandswitching in other designs,
and being motivated by the catacomb in the HRO
NC100X, I wonder if any have encountered bandswitching
by cam driven microswitches?

I presume that the contacts in microswitches must be
similar to those in small relays, and, being mechanical,
would not be subject to electrical failure.

What I envisage is that the most HF coils would be
mormally switched in by the microswitch closest
to the tuning cap, and then when the big cam (Big K? :-) )
slides along to activate that microswitch, the
next lower frequency coil takes over, and so on
and so forth.

Having had one failure by dropping the catacomb
mechanism on one corner, I'm sort of losing heart
at the prospect of making up 50 sliding contacts.

I remember the name "Tempatron" from way back in the 70's. They used
to make cam driven switches for fruit machines and the like.
And Begger me..they are still making them!!!

http://www.tempatron.co.uk/product.p...%20Timers.html

Learn from history. In the days of dual standard TVs (in the UK), some
makers had a large slide switch in the circuit board (this was the era
when even valve sets used PCBs with valve (tube) holders mounted on
PCBs. The switches were often operated by a bowden cable connected to
the VHF turret tuner. The switches had a huge number of contacts and
were infamous for failing- generally getting muck and gunge on them or
the contacts deforming. These were professionally produced items.

Using a similar approach with homemade contacts would seem doomed to
repeat a poor design concept. Learn from the errors of others.

On 11/07/2017 14:19, Rambo wrote:
On Tue, 11 Jul 2017 12:24:34 +0100, Brian Reay wrote:

On 11/07/17 11:50, Gareth's Downstairs Computer wrote:
Taking my cue from bandswitching in other designs,
and being motivated by the catacomb in the HRO
NC100X, I wonder if any have encountered bandswitching
by cam driven microswitches?

I presume that the contacts in microswitches must be
similar to those in small relays, and, being mechanical,
would not be subject to electrical failure.

What I envisage is that the most HF coils would be
mormally switched in by the microswitch closest
to the tuning cap, and then when the big cam (Big K? :-) )
slides along to activate that microswitch, the
next lower frequency coil takes over, and so on
and so forth.

Having had one failure by dropping the catacomb
mechanism on one corner, I'm sort of losing heart
at the prospect of making up 50 sliding contacts.

I remember the name "Tempatron" from way back in the 70's. They used
to make cam driven switches for fruit machines and the like.
And Begger me..they are still making them!!!

http://www.tempatron.co.uk/product.p...%20Timers.html

Not quite the same as sliding contacts doing the switching. Sealed
switches switches being closed by a cam are quite different to open
sliding contacts.

A cam isn't a contact.

Even you must recognise why the old mechanical telephone exchanges were
phased out.


Learn from history. In the days of dual standard TVs (in the UK), some
makers had a large slide switch in the circuit board (this was the era
when even valve sets used PCBs with valve (tube) holders mounted on
PCBs. The switches were often operated by a bowden cable connected to
the VHF turret tuner. The switches had a huge number of contacts and
were infamous for failing- generally getting muck and gunge on them or
the contacts deforming. These were professionally produced items.

Using a similar approach with homemade contacts would seem doomed to
repeat a poor design concept. Learn from the errors of others.

On Tue, 11 Jul 2017, Gareth's Downstairs Computer wrote:

Taking my cue from bandswitching in other designs,
and being motivated by the catacomb in the HRO
NC100X, I wonder if any have encountered bandswitching
by cam driven microswitches?

I presume that the contacts in microswitches must be
similar to those in small relays, and, being mechanical,
would not be subject to electrical failure.

Remember turret tuners? The coil came to the place where it was needed,
rather than long wires from a switch to the coils.

But, there was a time when diodes were seen as the way to go, using DC
voltage to turn on the diodes. So you weren't stuck with a big switch
running through things, or having to keep wires nice and short. I'm not
sure if this has gone far in more recent times, I suspect other things
have happened.

Get some small relays and use them. Though I don't know about small
relays that don't contribute to inductance.

In this modern age, redundancy gets around switches. Instead of switching
coils, use a transistor per band for each stage you need, and then
switching bands means switching which oscillator gets DC and which
amplifier gets DC, and maybe switching the signal path. But that's easier
than switching coils in and out of a circuit.

Make things as wideband as possible, then add filters as needed, switching
50ohm impedance rather than high impedance of an inductor.

One guy used to write about building shortwave receivers in CQ. He built
endless receivers, but most of them were single band. That has
advantages. In these days of DDS synthesizers, one could just build
single band receivers or transceivers, and then have one DDS synthesizer
to control them all.

Michael