In article ,
David Snyder Hale wrote:

It sounds an awful lot of money for something that you can make for less
than 5. I will hapilly make you one that will work just as well for 30
or if you have to buy one go for the Emtech ZM2. They are half the price
and work fantastically well. I bought one direct from the States for
about 60 and it is great up to 20W.

I do like to make my own equipment; in fact, I was about to put
together a little T match tuner when I came across the Qpak and read of
its low loss. But do tell, where can I find the parts for $5? Or even
$30? You generally can't get an enclosure and two BNCs for less than
$5. Yes, yes, you can stumble across deals, but I'd like to put
something together within a reasonable amount of time.

I'd be more comfortable with their claims of high efficiency, low
loss, and wide matching range if they actually provided some numbers.
It's true that some link-coupled tuners (e.g. a well-done Z-match)
have good matching range, but others (e.g. the Johnson Matchbox) have
a reputation for having a relatively limited matching range. The
devil's in the details.

As to losses: as I understand it, in a typical T-match tuner, most of
the losses occur in the coil, with only a small fraction of the loss
being in the capacitors. The claim of low loss in the "FlatPak"
variable caps may very well be quite true, but may also not be all
that relevant when comparing the QPak to more traditional tuners.

The "FlatPak" caps look interesting. I'd guess that they're a form of
butterfly cap, with fixed connections to one or two layers of
butterfly plates, plus and a single rotating stator. Maybe a very
narrow plate plate spacing and some form of insulating dielectric
(Teflon sheet)? This would allow for relatively high maximum
capacitance, low minimum capacitance, shallow depth, and reasonable
maximum standoff voltage. The sealing and gasketing of the caps may
very well be a necessity... you really wouldn't want to get dust or
dirt in between the plates and dielectric!

[A guy in our local ham club showed off a built-completely-from-scratch
T-match tuner last year, with disc-shaped caps built along these same
lines and a homemade roller inductor. Very atypical-looking device,
striking and quite beautiful. It beat out my own project to take
first place in the competition, and it certainly deserved the win!]

The toroidal coils in the QPak look nicely done, and I'd guess that
their power handling capacity is well beyond the 25-to-50-watt rating
of the tuner. I'd guess that the tuner's power handling capability is
limited by the maximum voltage across the caps, when working into
difficult loads. Arcing over an air-variable cap can be spectacular,
but I suspect that arcing over one of the FlatPak caps might burn the
dielectric badly enough to permanently damage it.

--
Dave Platt AE6EO
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