Hi,
Strips of PCB mounted edgewise was how I solved the space and
shielding problem. Still required some feedthrough caps to pass
DC and control voltages.
Allison
KB1GMX
--- In BITX20@..., Rahul Srivastava <vu3wjm@y...> wrote:
Hi!
Thanks for the tips and suggestion. Idea of Altoid tin reminds me of
the excellent Qptimised QRP transceiver. BITX though is full blown design.
I would try assenbling stages on .7 inches pcb strips and secure
them verticaly ie just solder the bottom edge to box , extra peice
between stages can provide shielding.
PA I would like to redo somethind on the lines of ATS sprint , low
power and better efficiency.
Let me arrange a tin for now of this size.
73
Rahul VU3WJM
Allison Parent <kb1gmx@a...> wrote:
Go for it, thats a real challenge.
I've put what amounts to the recieve side of a Bitx in a altoids tin.
That was easy, the knobs are always a problem. Seriously, the real
problem was keeping the BFO from swamping the RF amp from being so
close. Shielding was the required item to solve that. It's also
needed so that the Xtal filter can do it's work rather than blow by.
I also found SMT parts very handy.
The VFO is a problem. Heat, or rather heat transfer from other parts
will have to be attended to or the drift will be tough to manage.
Any case flex or the lid moving also caused frequency shifts. I
had enough heat from the audio too induce drift. You may wish to
consider a VXO at 24mhz (20m, IF at 10mhz and LO at 24mhz). A
higher freq VXO will tune more.
You can use FT25-43 toroids or BN43-2402 binocular cores for the
transformers as they are small. The turns ratio is all you need for
those as 8-10 turns will be enough. Consider using TUF1 DBMs as they
are very small and would save space over a core and diodes for the
modulator and mixer. You'll have to use shielded cans (maybe IF
transformers rewound) for the bandpass filter. The crystals
used for the filter and BFO consider the hc49 size or smaller.
The transmit chain will have to scale back. The size of the parts and
the current they need to handle presesnts limits for thermal and
RF isolation with conventionally available parts. Running without
the IRF510 can get you about 300MW with a good transistor and the
right output match.
You will have to use electronic TR switching, space for relays is
scarce. Antenna, Mic and earphone jacks must be small too.
It can be done but a lot of care will me needed to render a useful
radio.
Oh, I do have a larger Altoids tin it's nearly 3x the size
of the usual one. That would be easy.
Currently I'm building a BITx for 6M in a computer AB switch box
measuring of 7.25"Dx5.25"Wx2"H and I'm finding that fairly roomy.
the 5.25"x2" pannel space is cramped for space to accomodate
tuning, audio gain, mic and headphone jacks and S meter.
Allison
KB1GMX
--- In BITX20@..., Jim Strohm <jstrohm@e...> wrote:
On Sep 10, 2005, at 1:37 PM, Rahul Srivastava wrote:
Unfortunately I do not get Altiods here in Lucknow so a rough
dimension will be helpful this looks like a neat challenge.
2.25 x 3.75 in.
Whoops, 5.7 x 9.5 cm
0.75 in deep (2 cm)
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