Re: Altoids tin? go small???

Allison Parent <kb1gmx@...>
 

Hello Arv,

If you really want to push for tiny I have a design similar to
epiphyte but does not switch the LO and BFO. It uses two Sa602s
as bidirectional mixers and diode switching. The trick is that
the 602 has two inputs and two outputs and can be used bidirectionally
saving parts. I tried it.

--- In BITX20@..., "Arv Evans K7HKL" <arvevans@e...> wrote:
Miniature BITX builders:

Using a brass-screw type PTO also makes the VFO section much
more compact, without compromising slow and precise tuning,
but like Hans says, you will then need some sort of frequency
counter to determine where you are in the band.
Actually I've found the brass screw style once you have some kind
of dial or counter on them have excellent linear tuning and
resetability.

The PLL for the 6M is compact. I can still fit more in it if
needed and it's about 1/2 the size of an altoids tin. It only
contains 3 crystals, 1 16pin dip, 3terminal regulator, 7 transistors,
three diodes, and two adjustable coils two ferrite transformers.
Plus a fair number of bypass caps, coupling caps, and biasing
resistors. The package is 5 pieces of PCB material soldered to form a
box. Smaller would be possible with surface mount parts.

hopefully soon I can load a picture and schematic.

You can use very small low-voltage type capacitors (5 Volt rated
units)
for the emitter bypass caps because the operating voltage will not
exceed
that amount. Same applies to some other caps if you check the maximum
voltage that they might be exposed to.
If you have a copy of EMRFD there is a bidirectional amp that uses
fewer parts. I could upload an image of that amp. It's only 5 caps
all .1uf, 2 100ohm, 2 680ohm, 1 1Kohm, 2n3904 and 2n3906. Both ports
are 50 ohm and it's 16.8db to 40mhz. I tried it and found it as
advertized and compact.


Chip type resistors and capacitors are actually not too bad to
work with in ugly-construction method, and they will save
additional space.
They work very well, better than leaded.

With GI (galvanized iron roof flashing) material or double-sided PCB
as
the sub-strata you can build on both sides of the board. This also
saves
significant space.

If you use earphones only, or an external AF amp & speaker (PC
speakers
work well) you can eliminate the space required for the LM386 or other
high power AF amplifier circuit.

The whole microphone amplifier section (including VOX) might be built
inside the microphone instead of inside your miniature BITX chassis.

An IC socket on the rear panel might provide all the external
connections. Use a IC-type header plug to make connections to the rig.

Hans' G0UPL has a "FAST H&P Design"
<http://www.hanssummers.com/radio/huffpuff/minimalist/fast/> that
incorporates both VFO and stabilizer into a two-chip layout. This
makes
the VFO rather compact and still includes step-locked tuning for
very good
stability. You can further decrease the size of Hans design by
making the
VFO tuning a PTO where a brass screw tunes the VFO/PTO and
eliminates the
need for a large pot to adjust the frequency.

Relay based T/R switching can be replaced with solid-state switching
methods that are probably more compact than even miniature relay
units.

Yes, much smaller easier to layout.

This will also conserve power by elimination of current required by
the
relay coil.

Arv K7HKL
_._

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