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
2) RX band filters: I have decided to have a fixed capacitor and adjust the
inductor.The availability of adjustable coils (Toko for example) has
decreased in the last few years. Digikey only stocks a few of them but that
should be OK in the near term.
3) First IF filters: not much choice since 10.7MHz and 21.4 MHz seem to be
the only 2 frequencies stocked (most commercial boxes use between 35 and 70
MHz). The IF inductors/transformers at 10.7 MHz and 455 KHz have
disappeared from Digikey (used to be there a few years ago).
4) 2nd IF + FM demodulator. The Motorola parts (MC33xx) are gone. The part
that is found in many commercial XCVR is the Toshiba TA31136. This part is
not stocked by Toshiba's distributors in the US (12 weeks lead time if you
want to order 2K of them). Good news is that the Rohm BA4116FV is a
pin-to-pin compatible device and it is available at Digikey for $1.26. I
don't know if this part works since I have not seen it used anywhere...
5) 2nd mixer crystal. The 10.245 MHz crystals are easily available but not
the 21.4 +/- .455. This seems to remove the option of using a 21.4 MHz IF..
6) 2nd IF filter. The 455 KHz ceramic filters seem to have a very limited
availability. The exact type recommended by the IC vendor is hard to find..
7) FM discriminator. I could not find a source for the ceramic
discriminator recommended by Toshiba/Rohm (CDLBLA455KCAY24-B0 which is the
new P/N for the CDB450C24). I can understand the pain of the distributors
since every FM IC requires a different discriminator. The discriminator coil
that can be used instead is not easier to locate.
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...
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 !
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.

"Bernard" ) writes:


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 !
But amateur radio has always been about scrounging. Once you know enough,
you can make do in a lot of cases with what's available rather than
what's specified. Indeed, over the decades many an article has
been based on what the author had at hand (or in some cases what he
thought would be readily available) rather than because there was
something special about the parts. A beginner suffers from not
knowing enough, and going down to the parts store with the list of
parts and having no choice but to live with the prices, or if
the parts aren't available. But once they have a more extensive
understanding, they know that they can pull those bypass capacitors
off that VCR, and use those generic transistors instead of the generic
transistors specified in the article.

$45 is kind of expensive. Take any older cordless phone, and
one is bound to find a double conversion (10.7MHz and 455KHz)
FM receiver, often using one of those Motorola ICs. You can
get them cheap at garage sales over here, I've stopped bothering
with them because they are still plentiful (though I suppose
a later generation will be less useful, being more compact and
maybe using different IF frequencies). Indeed, buy the handset
and the base unit, and you get two IF strips. The ones I've
taken apart have a ceramic 10.7MHz filter, of the type you'd
find in an FM broadcast receiver, but that happens in a lot of
stuff. (Note there are some exceptions, where the units
are single converstion dropping from 49MHz to 455KHz, but the
one I picked up like that did still use one of those Motorola
ICs.)

Before FRS took off, there were license free 49MHz superhet
walkie talkies, that had dual conversion receivers with
the better ones, and they could be adapted with a change of
front end coils. These have faded away, so I don't know how
available they are (I once bought a pair for twenty dollars
at a garage sale), but they're is nothing forbidding their
use.

Baby monitors maybe, but I've never taken one apart and
because of their use I have my suspcions that they may be
single conversion, and perhaps even superregen.

Old cellphones, the bigger and clunkier the better, offer
up narrow band FM IF filters, and even complete IF strips.
The first IF will usually be in the 45MHz or higher range,
but given that they do include the conversion crystal to
455KHz, it doesn't really matter. The older ones are cheap
now, and the further back you go the more discrete components
you'll see. They'll be through-hole ICs, and identifiable,
rather than more recent ones that are surface mount and much
higher density where you can only use the ICs for the intended
purpose.

One problem that has arisen is that construction articles
in recent decades have become more about providing a kit to
the builder. Expect the builder to copy it perfectly, buy
the exact parts, and maybe even buy it as a kit from the author
or a third party. Once that happens, the author focuses on
using parts that are easy to come by, and the article is about
"building it like this" instead of explaining the philosophy and
possible alternatives to the parts. But it's only through understanding
that people can look at a schematic and realize they can use
that filter they have. The more they are spoon fed the more dependent
they become.

Michael VE2BVW

"Bernard" wrote in message
news:5Wwie.9489$jj.5508@lakeread06...
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
2) RX band filters: I have decided to have a fixed capacitor and adjust
the inductor.The availability of adjustable coils (Toko for example) has
decreased in the last few years. Digikey only stocks a few of them but
that should be OK in the near term.
3) First IF filters: not much choice since 10.7MHz and 21.4 MHz seem to be
the only 2 frequencies stocked (most commercial boxes use between 35 and
70 MHz). The IF inductors/transformers at 10.7 MHz and 455 KHz have
disappeared from Digikey (used to be there a few years ago).
4) 2nd IF + FM demodulator. The Motorola parts (MC33xx) are gone. The part
that is found in many commercial XCVR is the Toshiba TA31136. This part is
not stocked by Toshiba's distributors in the US (12 weeks lead time if you
want to order 2K of them). Good news is that the Rohm BA4116FV is a
pin-to-pin compatible device and it is available at Digikey for $1.26. I
don't know if this part works since I have not seen it used anywhere...
5) 2nd mixer crystal. The 10.245 MHz crystals are easily available but not
the 21.4 +/- .455. This seems to remove the option of using a 21.4 MHz
IF..
6) 2nd IF filter. The 455 KHz ceramic filters seem to have a very limited
availability. The exact type recommended by the IC vendor is hard to
find..
7) FM discriminator. I could not find a source for the ceramic
discriminator recommended by Toshiba/Rohm (CDLBLA455KCAY24-B0 which is the
new P/N for the CDB450C24). I can understand the pain of the distributors
since every FM IC requires a different discriminator. The discriminator
coil that can be used instead is not easier to locate.
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...
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 !
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.

I agree with Michael. A Radio/TV repair shop where they dispose of old
circuit boards or equipment that cost more $$ to repair ... gold mine of
parts (some discontinued -- just start desoldering)

DSP-10 designed by Bob Larkin, W7PUA. Kits on sale at Dayton and through
TAPR. For more information see http://www.proaxis.com/~boblark/dsp10.htm

gb

"Bernard" wrote in message
news:5Wwie.9489$jj.5508@lakeread06...
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).

Also try Dan's Small Parts for a variety of home builder parts
http://www.danssmallpartsandkits.net/

gb

Bernard, Michael: Thanks for this wonderful question and great answer.
Yea, scrounging and making do with what is available is the way to go.
There's a great book "First Light" by Richard Preston. It is about the
Palomar Mountain telescope. There is a section on the technical team
that builds the modern instruments used with the old 'scope. They got a
lot of their best parts by "dumpster diving" in California.
73 Bill M0HBR, CU2JL, N2CQR
http://planeta.clix.pt/n2cqr


Michael Black wrote:

"Bernard" ) writes:

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 !
But amateur radio has always been about scrounging. Once you know enough,
you can make do in a lot of cases with what's available rather than
what's specified. Indeed, over the decades many an article has
been based on what the author had at hand (or in some cases what he
thought would be readily available) rather than because there was
something special about the parts. A beginner suffers from not
knowing enough, and going down to the parts store with the list of
parts and having no choice but to live with the prices, or if
the parts aren't available. But once they have a more extensive
understanding, they know that they can pull those bypass capacitors
off that VCR, and use those generic transistors instead of the generic
transistors specified in the article.

$45 is kind of expensive. Take any older cordless phone, and
one is bound to find a double conversion (10.7MHz and 455KHz)
FM receiver, often using one of those Motorola ICs. You can
get them cheap at garage sales over here, I've stopped bothering
with them because they are still plentiful (though I suppose
a later generation will be less useful, being more compact and
maybe using different IF frequencies). Indeed, buy the handset
and the base unit, and you get two IF strips. The ones I've
taken apart have a ceramic 10.7MHz filter, of the type you'd
find in an FM broadcast receiver, but that happens in a lot of
stuff. (Note there are some exceptions, where the units
are single converstion dropping from 49MHz to 455KHz, but the
one I picked up like that did still use one of those Motorola
ICs.)

Before FRS took off, there were license free 49MHz superhet
walkie talkies, that had dual conversion receivers with
the better ones, and they could be adapted with a change of
front end coils. These have faded away, so I don't know how
available they are (I once bought a pair for twenty dollars
at a garage sale), but they're is nothing forbidding their
use.

Baby monitors maybe, but I've never taken one apart and
because of their use I have my suspcions that they may be
single conversion, and perhaps even superregen.

Old cellphones, the bigger and clunkier the better, offer
up narrow band FM IF filters, and even complete IF strips.
The first IF will usually be in the 45MHz or higher range,
but given that they do include the conversion crystal to
455KHz, it doesn't really matter. The older ones are cheap
now, and the further back you go the more discrete components
you'll see. They'll be through-hole ICs, and identifiable,
rather than more recent ones that are surface mount and much
higher density where you can only use the ICs for the intended
purpose.

One problem that has arisen is that construction articles
in recent decades have become more about providing a kit to
the builder. Expect the builder to copy it perfectly, buy
the exact parts, and maybe even buy it as a kit from the author
or a third party. Once that happens, the author focuses on
using parts that are easy to come by, and the article is about
"building it like this" instead of explaining the philosophy and
possible alternatives to the parts. But it's only through understanding
that people can look at a schematic and realize they can use
that filter they have. The more they are spoon fed the more dependent
they become.

Michael VE2BVW

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.





--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Michael,

I did not intend to turn this thread into a philosophical debate (I had
enough with the "no progress in decades" thread" !) but your are bringing a
good point.

I should have stated more clearly that my intend is what you describe as
"providing a kit to the builder". We may debate (please don't !) on the
value that this brings to the builder. On a 1 to 10 scale, buying a
transceiver is a 0 and building it from raw silicon, carbon and copper is a
10+. Where does building a "kit" from an article stand on that scale ? I
guess somewhere between 1 and 9. But I am going to firmly defend the fact
that it is more than zero. I can find many projects that anybody can build
with spares (like many "one transistor radio") but I also believe that to go
beyond that you need a PCB and an orderable parts list... When this is done,
some may chose a path that will teach them a lot. More than 25 years ago, I
did many mods on the first 2-meter FM transceiver that I owned. It was fun
but finding the spare Japanese IC's that I burned in the process was a
nightmare ! I whish I had done these mods on a XCVR that I built, even if I
had to buy the PCB and the key components.

Good point on the 49 MHz intercom. I have a pair of them. And you are right,
they have a wideband ceramic filter at 10.7 MHz. I guess they need to
because they share the second conversion Xtal with the PLL (10.240 MHz) so
the IF is really at 10.695 MHz (2nd if is at 455 KHz). This is confirmed by
looking at the PLL datasheet. The bad news is that the PLL has a 60 MHz max
input with preprogrammed channels. By the way, my intercom is not
full-duplex but the phones are. May be somewhere someone is running a
repeater with modified 49 MHz phone !

Thanks again !
Bernard


"Michael Black" wrote in message
...

"Bernard" ) writes:


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 !
But amateur radio has always been about scrounging. Once you know enough,
you can make do in a lot of cases with what's available rather than
what's specified. Indeed, over the decades many an article has
been based on what the author had at hand (or in some cases what he
thought would be readily available) rather than because there was
something special about the parts. A beginner suffers from not
knowing enough, and going down to the parts store with the list of
parts and having no choice but to live with the prices, or if
the parts aren't available. But once they have a more extensive
understanding, they know that they can pull those bypass capacitors
off that VCR, and use those generic transistors instead of the generic
transistors specified in the article.

$45 is kind of expensive. Take any older cordless phone, and
one is bound to find a double conversion (10.7MHz and 455KHz)
FM receiver, often using one of those Motorola ICs. You can
get them cheap at garage sales over here, I've stopped bothering
with them because they are still plentiful (though I suppose
a later generation will be less useful, being more compact and
maybe using different IF frequencies). Indeed, buy the handset
and the base unit, and you get two IF strips. The ones I've
taken apart have a ceramic 10.7MHz filter, of the type you'd
find in an FM broadcast receiver, but that happens in a lot of
stuff. (Note there are some exceptions, where the units
are single converstion dropping from 49MHz to 455KHz, but the
one I picked up like that did still use one of those Motorola
ICs.)

Before FRS took off, there were license free 49MHz superhet
walkie talkies, that had dual conversion receivers with
the better ones, and they could be adapted with a change of
front end coils. These have faded away, so I don't know how
available they are (I once bought a pair for twenty dollars
at a garage sale), but they're is nothing forbidding their
use.

Baby monitors maybe, but I've never taken one apart and
because of their use I have my suspcions that they may be
single conversion, and perhaps even superregen.

Old cellphones, the bigger and clunkier the better, offer
up narrow band FM IF filters, and even complete IF strips.
The first IF will usually be in the 45MHz or higher range,
but given that they do include the conversion crystal to
455KHz, it doesn't really matter. The older ones are cheap
now, and the further back you go the more discrete components
you'll see. They'll be through-hole ICs, and identifiable,
rather than more recent ones that are surface mount and much
higher density where you can only use the ICs for the intended
purpose.

One problem that has arisen is that construction articles
in recent decades have become more about providing a kit to
the builder. Expect the builder to copy it perfectly, buy
the exact parts, and maybe even buy it as a kit from the author
or a third party. Once that happens, the author focuses on
using parts that are easy to come by, and the article is about
"building it like this" instead of explaining the philosophy and
possible alternatives to the parts. But it's only through understanding
that people can look at a schematic and realize they can use
that filter they have. The more they are spoon fed the more dependent
they become.

Michael VE2BVW

"Tim Wescott" wrote in message
...
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)


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".
-------------------------------------------
Tim Wescott


Seattle Robotics is the group that uses the toaster oven for reflow. It
actually works very well !
'Have you seen my new soldering Iron? by Kenneth Maxon
http://www.seattlerobotics.org/encod...6/oven_art.htm

g. beat
w9gb

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.

You are right, for example most of the 802.11 or Bluetooth solutions are
zero-IF, but I don't think that this is ideal for Ham Radio (the main issue
is re-injection of the LO into the RX). A better option (for us) is the low
IF option (like in the DSP10). The DSP10 has an IF at 19.665 MHz and one at
15 KHz. The concept is excellent but slightly overdesigned for what I want
to achieve. The drawback (when compared to zero-IF) is that the low-IF
receivers still requires dual conversion and IF filters to achieve any level
of performance.

You are right, for example most of the 802.11 or Bluetooth solutions are
zero-IF, but I don't think that this is ideal for Ham Radio (the main issue
is re-injection of the LO into the RX).

Bernard,

If your goal is to make a kit that uses simple, commonly available
components and exploits a 'powerful microprocessor' for flexibility, then
DSP is definitely the way to go. If properly done, it virtually eliminates
the need for all of the old ham-favorite special function chips.

With respect to 're-injection of the LO into the RX', I'm not quite sure
what you mean. There is the potential for LO leakage out of the antenna port
because the LO is on the receive frequency, but this is pretty easily
managed with careful electrical and electro-mechanical design.

Joe
W3JDR


"Bernard" wrote in message
news:FeBie.17870$ye1.3226@okepread06...
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.

You are right, for example most of the 802.11 or Bluetooth solutions are
zero-IF, but I don't think that this is ideal for Ham Radio (the main
issue is re-injection of the LO into the RX). A better option (for us) is
the low IF option (like in the DSP10). The DSP10 has an IF at 19.665 MHz
and one at 15 KHz. The concept is excellent but slightly overdesigned for
what I want to achieve. The drawback (when compared to zero-IF) is that
the low-IF receivers still requires dual conversion and IF filters to
achieve any level of performance.