"sipa" wrote in message
...
another problem is that cb transciever legaly must be registered (and
payed
fee), but reciever dont need it...

best regards from sunny Croatia! (9A, 328, HR)
www.hr
and my hometown www.sibenik.hr

Sipa

Thank you for the nice links. Although the language is something of a
barrier over on this side of the pond, "Foto-galerija" isn't so tough to
figure out g Looks like a pretty town.

A single frequency receiver should be fairly simple to build.
Unfortunately, most of the really simple things you see online are
transceivers, and those are typically for 7 MHz, which is a slightly
different problem than 27 MHz.

If you don't need a lot of sensitivity, and since you are interested in
receiving CW, you may be able to rip off one of the many designs that use a
VXO and a 602 mixer in a direct conversion design. I haven't personally
built such a thing for 27 MHz, but I have had some success at 21 MHz with a
dirt-simple design.

One challenge you will have is that the simplest designs rely on a crystal
for your receiving frequency. These need to be custom made and as a result
are fairly expensive (around 12 euro). An alternative is to use a
programmable oscillator. These are a lot cheaper (under 3 euro) but are far
from ideal for a receiver. Nevertheless, if you don't have strong stations
nearby your channel 12 signal, it might be useable. Again, I have made this
work at 21 MHz, but it is far from perfect.

One confusing factor ... the NE602 mixer, which is very popular for this
sort of circuit, has undergone a number of changes in manufacturer and
testing protocols. The result is that, although the circuits usually call
for an NE602, you usually can't get one of those. However, the NE602,
NE612, SA602 and SA612 are all the same part. The 604/605/614/615 are the
same part with some extra stuff on the chip that you don't need to use.

You might put some sort of filter in front of the 602, but basically your
antenna goes into the 602's RF port. The crystal or programmable oscillator
goes into the LO port, and the audio out is taken into an amplifier chip
like the LM396 or 380. The only hard part is that you need to be a little
careful about lead lengths because both the 602 and the 396 have astonishing
amounts of gain and want to oscillate if you look at them the wrong way!

If you rummage around on the web, you will probably find hundreds of
receivers with this basic model, although not for 27 MHz. All you need to
do is recalculate the stuff between the 602 and the antenna for 27 MHz
instead of the frequency for the model you find. You will want more gain at
27 MHz than for 7, so you may want to take a look at the 396/380 combination
that Elecraft uses in the K1 instead of the lone 396 that many designs use,
depending on how much audio you need. My 21 MHz receiver using only a 396
was pretty marginal, although useable.

The other issue with the 602 is that it is prone to issues with nearby
signals. In western Europe this is a big problem at the lower frequencies
where the airwaves are very crowded. If you have plenty of strong signals
close to your channel 12 signal you may need to go to a different approach.
The problem is that the passive mixers that work well in this environment do
require additional circuitry, which is significant when you are aiming for
as cheap and simple as possible.

Hope this helps a bit

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