Bernard wrote:
I have looked at homebrewing an FM 2-meter XCVR and already got help from
this group. The goal is to spend time on something that others could
duplicate and not work on a one of a kind.
First, why homebrewing ? Two reasons:
1) It is homebrewed
2) There is room for a "powerful" microprocessor that will do other things
(APRS is one of them)
It seems that the problem is the selection of components that can be sourced
in relatively low volume and at a reasonable cost by amateurs (read:
Digikey, Mouser and alike).
Here is what I have found some far:
1) Transistors for RX front end: relatively easy to find if based on
dual-gate MOSFET
Last time I looked Digi-Key had a good selection of NEC parts.
2-7, various RF part complaints)
The world seems to be going to direct-conversion I-Q receivers with the
baseband going to a DSP for processing. Reverse for TX. I think this
would work fine for any mode on 2m, including FM if you're clever with
your algorithms.
8) PLL: I am currently leaning towards National (LMX2306 or similar). They
are cheap and available. NS has a nice PLL design tool online but the tool
tries to convince me to switch to a better a part that I won't be able to
handle (leadless package). It is clear that the new generations IC's are not
designed for hand soldering at home...
This is why God made Toaster Ovens. Do a web search on "toaster oven
reflow".
9) Microprocessor and display: no problem here , plenty of choice.
10) TX chain transistors and PA Module: no problem with the regular vendors.
www.rfparts.com seems to have a large selection of modules.
11) TX low pass filter: will need to be hand made. That's OK but who is
selling tinned wire ?
Some notes:
1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13
grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a
11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz
ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate
mosfet (unidentified), a 3.3V regulator and more. I am not sure what to
think except that this might be a non traditional way to source 1/2 of the
RX section !
Not a bad way to go.
2) Some hard to find parts are sometime available as spare for Ham or
commercial radios but the prices are generally too high to be considered.
3) One way to go around the hard to find parts is to go with a more
discrete solution (no IF/Mixer/DEMOD/SQUELCH IC) and hand wire all the
inductors. This is not the way I am planning to go.
4) English is my 2nd language. Excuse the grammar mistakes and hard to
understand sentences.
Your written English is most definitely up to par -- if you hadn't
mentioned it I wouldn't be able to tell that you're not a native speaker.
--
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com