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

1) It is homebrewed
2) There is room for a "powerful" microprocessor that will do other things
(APRS is one of them)

Nice goals, but your target market will be kind of limited. Whatever you
come up with is going to cost 2-4x commercial. I can't really see the point
of APRS. A nice, compact, inexpensive APRS box would be nice, but a
homebrew VHF rig isn't going to get there. Now, maybe a little box with a
TNC and GPS built in that would plug into an HT might come close, but that's
not what you are focusing on here.

2) RX band filters: I have decided to have a fixed capacitor and adjust
the
inductor.

That does make for harder parts selection. Why that choice?

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..

10.7 is a pretty low first IF. You might consider using a higher IF and
winding the transformers on toroids.

8) PLL: I am currently leaning towards National (LMX2306 or similar).
They

Think about DDS. There are some really nice DDS choices from Analog Devices
and TI. TI has some really nice, cheap synthesizers. DDS is way less of a
pain than PLL. TI's 440 MHz part can easily work down to 2 meters. Yes,
they are pretty much all TSSOP but that is manageable to hand solder on a
PCB. Messy to prototype but then that will be a problem at VHF anyway.

...

On Wed, 18 May 2005 10:41:19 GMT, W3JDR wrote:

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

If I remember rightly, there's a description of a DSP-based 2m transceiver
in 'Experimental Methods in RF Design...'

73

John, G4GOY

"Tim Wescott" wrote in message
...

This is why God made Toaster Ovens. Do a web search on "toaster oven
reflow".

Most of the DDS and PLL chips are available in TSSOP. You don't need a
toaster oven for that, your typical soldering iron works just fine. Now, if
you had to resort to a BGA that would be a different story.

I would encourage Bernard to consider mostly SMT parts. SMT resistors and
caps are a lot more convenient than leaded, and a lot smaller. Eliminates
any issues with lead inductance, too. Maybe a little more expensive,
though.

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.

I agree

...

1) Transistors for RX front end: relatively easy to find if based on
dual-gate MOSFET

OK, but you can get better noise figure from a GaAs part.


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.

Mouser stocks a VERY nice line of low cost VHF shielded inductors. Google
"xicon" and "tunable coil" on the Mouser website.



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).

Again, Mouser is your friend -- google "xicon" and "transformer". If I were
doing it, I'd do a 70 MHz. first IF and then 10.7 MHz. second IF. Forget
dropping down to 455 unless you have to.


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...

Phillips makes (made??) a nice line of FM ICs. You might give them a try.



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..

Why crystals? You are going to have a synthesizer for the front end anyway,
why not use the synthesizer crystal as your timebase and synthesize the
mixer oscillator? You said you wanted some stuff for the microprocessor to
do anyway; controlling a synthesizer is one of them. Or, you could get a
parallel input synthesizer and hardwire it to a fixed frequency.


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.

A discriminator (or ratio detector) is nothing more than a couple of
transformers coupled bottom to top. You can make a two-coil ratio detector
as easy as buying one.


11) TX low pass filter: will need to be hand made. That's OK but who is
selling tinned wire ?

Why would you need tinned wire? Plain old magnet wire is easy to come by.


Jim

Thanks for all the comments. Here is some feedback:

The Palomar telescope: quite an interesting story. My answer: would it be
better if many could build their own with parts from Sears and Home Depot or
is it better as a one of a kind made from Southern California trash ?

DSP10: definitely a very good design but with a different goal. I think that
adding a DSP substantially increases the barrier to entry but I take note
that this was suggested a few times (even if it will end up just replacing a
$1.26 demodulator). In the TX chain the DSP implementation is actually more
complicated because it would require an additional mixer (assuming that the
only goal is FM) instead of directly modulating the VCO.

Taking parts from Radio and TV: this is how I got started in electronic 30
years ago. I would not suggest it to someone who is starting in the hobby.
One reason is Murphy. This TV might be in the dumpster just because the one
part you need failed !

Dan's Small Parts (http://www.danssmallpartsandkits.net/): very good, thanks
for the link. I would sometimes want more information about some parts but I
guess this is why there is a phone number to call.

Toaster reflow: I will look into this but this getting border line for me !
I decided a few years a go to stop making my own PCB's and order them online
(APC circuit or alike). I may do the same for soldering !

Market for APRS + XCVR: I am not looking at it in term of market but rather
combining 2 interests (RF and µP) on one platform.

Zero-IF: I don't know if this has been done in a decent 2-meter receiver. If
anyone has a pointer I would be interested

Experimental Methods in RF Design: it is on my list of book to buy now (if
you own this book, check the errata. They are online).

Mouser: I will have a better look at their line of inductors (by the way, I
prefer adjusting the inductor due to some old memories of melting adjustable
capacitors !)

Philips: yes I looked at them. The only part they have left is the SA615.
This market is more or less gone. The big professional users are moving to
digital voice...

TI: they have fast D/A (400 MHZ) out of which a motivated hobbiest could
build a DDS but I did not see synthesizers or DDS parts. I will double check
and have a second look at ADI's DDS

I will update the group after I make up my mind...

Bernard

Bernard wrote:

Thanks for all the comments. Here is some feedback:

The Palomar telescope: quite an interesting story. My answer: would it be
better if many could build their own with parts from Sears and Home Depot or
is it better as a one of a kind made from Southern California trash ?

DSP10: definitely a very good design but with a different goal. I think that
adding a DSP substantially increases the barrier to entry but I take note
that this was suggested a few times (even if it will end up just replacing a
$1.26 demodulator). In the TX chain the DSP implementation is actually more
complicated because it would require an additional mixer (assuming that the
only goal is FM) instead of directly modulating the VCO.

Taking parts from Radio and TV: this is how I got started in electronic 30
years ago. I would not suggest it to someone who is starting in the hobby.
One reason is Murphy. This TV might be in the dumpster just because the one
part you need failed !

Dan's Small Parts (http://www.danssmallpartsandkits.net/): very good, thanks
for the link. I would sometimes want more information about some parts but I
guess this is why there is a phone number to call.

Toaster reflow: I will look into this but this getting border line for me !
I decided a few years a go to stop making my own PCB's and order them online
(APC circuit or alike). I may do the same for soldering !

Market for APRS + XCVR: I am not looking at it in term of market but rather
combining 2 interests (RF and µP) on one platform.

Zero-IF: I don't know if this has been done in a decent 2-meter receiver. If
anyone has a pointer I would be interested

Experimental Methods in RF Design: it is on my list of book to buy now (if
you own this book, check the errata. They are online).

Mouser: I will have a better look at their line of inductors (by the way, I
prefer adjusting the inductor due to some old memories of melting adjustable
capacitors !)

Philips: yes I looked at them. The only part they have left is the SA615.
This market is more or less gone. The big professional users are moving to
digital voice...

TI: they have fast D/A (400 MHZ) out of which a motivated hobbiest could
build a DDS but I did not see synthesizers or DDS parts. I will double check
and have a second look at ADI's DDS

I will update the group after I make up my mind...

Bernard



I can see this will be a difficult project for you....maybe not
technically, but emotionally.

If I may say so...

I find homebrewing 'any something' falls into one of two broad categories.

One is to play around with the mind of experimentation, not to spend
too much money at the outset, to learn from the failures, and have the
project on the shelf eternally awaiting modifications for better
performance.... and typically at several times the cost of a commercial
ready-made equivalent.

Two - would be trying actually build something state-of-the-art and
trouble-free with the anticipation of actually using it on a daily
basis....and typically at several times the cost of a commercial
ready-made equivalent :-)

Neither is bad but they are entirely different disciplines to the hobby
of rolling your own and this has to be determined early on as you plan
the project. Most of us wind up somewhere between the two extremes. "It
works great, but..." Over-thinking the project often results in never
getting started.

-Bill

In article ,
says...
8) PLL: I am currently leaning towards National (LMX2306 or similar).
They

Think about DDS. There are some really nice DDS choices from Analog Devices
and TI. TI has some really nice, cheap synthesizers. DDS is way less of a
pain than PLL. TI's 440 MHz part can easily work down to 2 meters.

Maybe use an image from a plain old AD9850 or AD9851... no need for a
fast clock if you only want to cover a 4 MHz chunk of spectrum.

The National and Analog PLL chips are great, but not needed here.

-- jm

------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------

On Wed, 18 May 2005 08:54:23 -0700, "RST Engineering"
wrote:

1) Transistors for RX front end: relatively easy to find if based on
dual-gate MOSFET

OK, but you can get better noise figure from a GaAs part.

True, however most uses for 2m a good transistor or fet will be
adaquate and likely easier to use. GaAs fets are harder to use
and can easily take off at microwave and harder to find.

For real fast lashups I've used MAR or ERA (MiniCircuits) MIMICS
and they are the easiest way to get good stable and predictable
gain at VHF through microwave and a kit of 30pieces was
around 49$ (ERA 1,2, and 3types). Parts can be had for
under 2$US in singles. Compared to transistors, FETs and
GaAs devices they are noiser but for a lot of things a MAR6
at 3db and 20DB gain to 1000mhz is not shabby.

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.

Mouser stocks a VERY nice line of low cost VHF shielded inductors. Google
"xicon" and "tunable coil" on the Mouser website.

There are many suppliers. For 2m use it's possible to design with a
bandpass frontend easily and then tuning is less an issue. I just
wind coils and bend them as needed to tune. Programs to calculate
a coild for that are easy to find on the 'net.

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).

However for those who care to it's possibel to roll your own. Ladder
filters using very common 20 or 24 mhz clock crystals are do able.

Again, Mouser is your friend -- google "xicon" and "transformer". If I were
doing it, I'd do a 70 MHz. first IF and then 10.7 MHz. second IF. Forget
dropping down to 455 unless you have to.

Dual conversion using Murata and other 455khz filters is easy.
Motorola (3357 and friends) and other have a complete dual conversion
IF (everthing after first mixer) in a DIP and all you need is 10.7,
CFU455 filters and 455 if can for the quadarture dectector and 10.245
mixer crystal. These are easily ripped from:

Baby monitors, (flea markets and garage sales)
49mhz hts (non supperregen) (flea markets and garage sales)
Old scanners (flea markets and garage sales)
Other older radios that have been 4d (4d diseased, dying, dead
or decaying). (flea markets and garage sales)

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...

There are suppliers selling NOS motorola parts:

http://www.danssmallpartsandkits.net/ has them sometimes
http://partsandkits.com/parts.asp has the 3362 at 2 for 4$ (good
source for toroids, NE602 and other bits).

Phillips makes (made??) a nice line of FM ICs. You might give them a try.

The 604 can be hard to find.

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..

Often thats easy to substitute and wider (15kc) ones are easy to find.

Why crystals? You are going to have a synthesizer for the front end anyway,
why not use the synthesizer crystal as your timebase and synthesize the
mixer oscillator? You said you wanted some stuff for the microprocessor to
do anyway; controlling a synthesizer is one of them. Or, you could get a
parallel input synthesizer and hardwire it to a fixed frequency.

The only way to go unless you doing a repeater or other fixed
frequency application. One caveat, it's far easier to create a clean
crystal LO chain and for super low noise frontends the LO must also
have narrow noise sidebands.

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.

A discriminator (or ratio detector) is nothing more than a couple of
transformers coupled bottom to top. You can make a two-coil ratio detector
as easy as buying one.

True, the ratshlock PRO4, Pro12, series and the Pro7 series scanners
used a trnsistor 455khs IF and two common IF cans for a discriminator
with excellent results. The transistors were of the 2n2222/2n3904
equivelent class easily gotten form JDR at 4-6 cents each.

You can do a quadrature detector using a single IF can and a NE602
mixer.

11) TX low pass filter: will need to be hand made. That's OK but who is
selling tinned wire ?

Why would you need tinned wire? Plain old magnet wire is easy to come by.

Yep! tinned is not a requirement. Besides of you do it right you not
going to need much.

I've used MAR6 mimic (cheap from Minicircuits) as RF with a TUF1 DBM
feeding a MPF102 fet with it's output running into a textbook 3357 if
chain for both 2m and similar for 440 and it's clean, easy and plenty
of gain (sub .12 uv for 10db quieting FM). The Moto 3357 came from a
49mhz HT along with the 10.245 crystal, 10.7 filters and 455filter. I
used a moto 145170 pll for the LO. Since the 3367 also does metering
and squelch all it needed was audio (LM386-N). The front end was low
loss (1db) bandpass before the MAR6 and image stripping (Higher loss
bandpass) after the MAR6. the DBM can be one of a dozen different
parts had cheap or even hand made (1n914s work ok at 2m). The post
DBM fet was not optimized for gain only to buffer the DBM from the
Crytal filter (10.7mhz).

Of course of you want something as a kit Ramsy has a FM rx for
(FR146C is 2m, they have 10m, 6m and 220) that can be used for that
range and has fair rx performance but needs either crystal control
(NE602 VFO is not adaquately stable) or PLL either of which is usable
with that. (it's cheap too! 44.95$US). They do about .7 uV for decent
quieting and they do also sell a RF preamp thats decent. I've built
both and they work as expected using the VFO and better with crystal
control.

For experimentors its possible to do it. Parts even old ones are
often found from small suppliers at resonable prices. Like someone
said earlier learning where and what to look for is a big part of home
made radio systems. It also helps to learn how to strip and use "old"
parts.

Allison
KB1GMX

On Thu, 19 May 2005 00:57:24 -0400, -exray- wrote:

Experimental Methods in RF Design: it is on my list of book to buy now (if
you own this book, check the errata. They are online).

Must have as well as a Radio Amatuers Handbooks of differing years!


I can see this will be a difficult project for you....maybe not
technically, but emotionally.

If I may say so...

I find homebrewing 'any something' falls into one of two broad categories.

One is to play around with the mind of experimentation, not to spend
too much money at the outset, to learn from the failures, and have the
project on the shelf eternally awaiting modifications for better
performance.... and typically at several times the cost of a commercial
ready-made equivalent.

Two - would be trying actually build something state-of-the-art and
trouble-free with the anticipation of actually using it on a daily
basis....and typically at several times the cost of a commercial
ready-made equivalent :-)


Then there are people like me. I build in the middle. I often want
something that may not be state of the art (but still works excellent)
and is specifically not feature laden yet still require stable and
robust operation. I've done 6m transceivers that easily hear better
than the best and TX with a clean high quality signal that are not
state of the art. Please never equate the lack of state of the art
with well executed design as the latter can be as good or better due
to fewer compromizes that a production design might suffer. Shielding
is one matter where the homebrewer can easily exceed commerial.

Another area is designs where labor counts. Often my time is cheap
but using a commercial coil or crystal filter is not. So making my
own may factor $s for time.

Neither is bad but they are entirely different disciplines to the hobby
of rolling your own and this has to be determined early on as you plan
the project. Most of us wind up somewhere between the two extremes. "It
works great, but..." Over-thinking the project often results in never
getting started.

-Bill

That kills most projects! Sometimes it's "better" to plunge in and
have a few bits that fail or just done meet expectations. If the
midset is right you just redesign it, replace it and keep building.
Sometimes along the way you can also make a discovery
that will enlighten.

Allison
KB!GMX