I'm not locked in to the MC1350 - it just happens to be
what's used in the "ultra-cheap" kit I ordered. As it turns
out, there's a company (Lansdale.com) that seems to be
forming a business model around buying "obsolete" IP
from Motorola et.al. and keeping the parts available.
Interesting idea. As it happens, NTE has a drop-in
replacement part for the MC1350 in their "NTE746" -
available from Mouser. May be of interest to some on
this group???

The absolute minimum operating voltage for the MC1350 is 12 volts. Not
11.9, 12. If this is a mobile application, then figure on a switching power
supply to get you up to 15 volts or so.


Among that stuff is an HP8654A
good to about 520 MHz that I've never used (and for the
life of me can't figure why I bought 8-)........


Oh, I'll take it off your hands for $20 or so {;-)


Jim

"RST Engineering" wrote in message

The absolute minimum operating voltage for the MC1350 is 12 volts. Not
11.9, 12. If this is a mobile application, then figure on a switching
power
supply to get you up to 15 volts or so.

Thanks for that tip - it will be the first "improvement" to the cheapo
Ramsey receiver (which runs off 9 volts). The power supply is something
I *can* handle easily 8-)...

Among that stuff is an HP8654A
good to about 520 MHz that I've never used (and for the
life of me can't figure why I bought 8-)........

Oh, I'll take it off your hands for $20 or so {;-)
Jim

Well, give it a few weeks! Once the frustration level gets high
enough and I realize that I'm really a bit-banger and not a radio-head
I may be tempted to toss it (and anything else RF related) out the
window - in which case I'll pack it up and donate it to you 8-)...

In the meantime, any other suggested improvements or hints are
most appreciated (e.g. "up the IF from 10.7"?)...!

Thanks,
Bill (Who still thinks the universe *IS* digital - but infinite resolution
8-)

I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF
frequency) or 70 MHz. (satellite IF frequency), and then downconvert to
either 21.4 or 10.7...there are cheap crystal filters at both frequencies.

Jim


In the meantime, any other suggested improvements or hints are
most appreciated (e.g. "up the IF from 10.7"?)...!

Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

"RST Engineering" wrote in message
...
I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF
frequency) or 70 MHz. (satellite IF frequency), and then downconvert to
either 21.4 or 10.7...there are cheap crystal filters at both frequencies.

Jim


In the meantime, any other suggested improvements or hints are
most appreciated (e.g. "up the IF from 10.7"?)...!

I would go directly from 45MHz to 455kHz..............this is typical in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz
crystal used with the on-board oscillator allows you to derive your 2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator.
This is also a good system and it will give you fairly good strong signal
handling capability.

Pete

"Netgeek" wrote in message
...
Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

"RST Engineering" wrote in message
...
I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF
frequency) or 70 MHz. (satellite IF frequency), and then downconvert to
either 21.4 or 10.7...there are cheap crystal filters at both
frequencies.

Jim


In the meantime, any other suggested improvements or hints are
most appreciated (e.g. "up the IF from 10.7"?)...!

"Pete KE9OA" ) writes:
I would go directly from 45MHz to 455kHz..............this is typical in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz
crystal used with the on-board oscillator allows you to derive your 2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator.
This is also a good system and it will give you fairly good strong signal
handling capability.

Pete

I'd hesitated to post since I wasn't sure of the sort of selectivity needed.

But yes, if the selectivity is available at 455KHz, there's no need to
have something in between that and 45MHz (or for that matter, if the
right selectivity can be had higher, gain is the only reason for going down
to 455KHz.

Old cellphones, the big and bulky kind, have IFs in the above 30MHz range
(the exact frequency has varied, but I think the majority of those that I've
stripped have had 45MHz IFs. And they tend to drop down to 455KHz after
that, meaning a scrap cellphone (the older the better because they
are cheaper and the parts are bigger) will generally provide a "roofing
filter" and the crystal to get down to 455KHz from there, and even the
455KHz filter if it doesn't have to be narrow.

Michael VE2BVW

"Netgeek" wrote in message
...
Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

"RST Engineering" wrote in message
...
I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF
frequency) or 70 MHz. (satellite IF frequency), and then downconvert to
either 21.4 or 10.7...there are cheap crystal filters at both
frequencies.

Jim


In the meantime, any other suggested improvements or hints are
most appreciated (e.g. "up the IF from 10.7"?)...!

From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am

I would go directly from 45MHz to 455kHz..............this is typical
in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a
44.545MHz
crystal used with the on-board oscillator allows you to derive your
2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./
demodulator.
This is also a good system and it will give you fairly good strong
signal
handling capability.

Pete

"Netgeek" wrote in message
...
Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

As a suggestion (too late if parts are incoming), a
single conversion to a 21.4 MHz IF is quite suitable.
Using a monolithic quartz crystal filter (available
from DigiKey for about $15 a pair of two) between
the mixer and first IF could eliminate ALL tuned
circuits in the IF following the 1st IF amplifier.
Those are available in 12.5 KHz bandwidth which will
be fine for a VOR signal. [DigiKey has a link to
download specs for the ECS-made monolithics]

This is now common in mobile radios, both new and
retrofit of older ones.

If a single-conversion scheme with 21.4 MHz is done,
the LO can be 86.6 to 96.6 MHz with an image at
65.2 to 75.2 MHz. That is a low enough frequency
to allow a simple L-C "top coupled resonator" fixed
bandpass filter for the front end at 108 to 118 MHz
(8.9 % bandwidth).

Doing double conversion with a first IF of 45 MHz
is, by itself, no problem. However the 2nd IF image
is a bit too close to the nominal bandwidth of any
45 MHz 1st IF tuning (it's only 0.91 MHz away). With
the second's image (on either side depending on 2nd
LO above or below 45 MHz), there's still a chance to
pick up part of the FM BC band locally. To avoid
that, the 2nd LO should be on the high side of 45.
Second IF image would then fall into the low end of
the 118 to 137 MHz comm band (also AM) and those
transmitters are much lower powered ones than BC
stations.

With a 10.7 MHz 2nd IF, its image would be 21.4 MHz
away and rather easy to attenuate in the 45 MHz 1st
IF. There's only a slight problem using stock
10.7 MHz IF components: Bandwidth of the whole 2nd
IF might be around 160 KHz; less discrimination to
nearby VORs and Localizers. A study of FAA sectional
charts might be called for to check on potential
interfering stations although those are assigned in
regards geographic locations to minimize normal
interference.

I agree about the 21.4MHz I.F. in a single conversion scheme. If the
required gain is achievable, this is a very good way to go. I remember one
of the Rockwell-Collins ADF receivers that had this setup.
As far as a 45MHz 1st I.F.............. these crystal filters seem to be
designed with a 455kHz 2nd I.F. in mind because a 910kHz rejection spec is
given. I have used that scheme over the years with a diode ring mixer as the
1st mixer. I follow the mixer with a series L, shunt C as the second leg of
a diplexer that matches the 50 ohm output of the mixer to the crystal
filter............ The first leg being is a parallel LC tuned circuit that
is in series with a 50 ohm idler resistor. With a reactance of the LC
elements of around 47 ohms, the selectivity at 6 db is approximately 15kHz.
The (2 time 2nd I.F. image rejection ) is about 60dB when using four poles
at 45MHz. I haven't done any in-band spur calculations with this scheme for
the aircraft band but I think that with high-side injection it would be ok.
Of course, if a 25kHz tuning step is used I am not sure how it would affect
the phase noise of the synthesizer if a Fractional N topology wasn't used. I
an NE602 is used as the 2nd mixer and just the I.F./ demodulator sections of
a TDA1572 were used, the only adjustment required would be a trimmer
adjustment of the 2nd LO in order to have a symmetrical adjacent channel
response.

Pete

wrote in message
oups.com...
From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am

I would go directly from 45MHz to 455kHz..............this is typical
in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a
44.545MHz
crystal used with the on-board oscillator allows you to derive your
2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./
demodulator.
This is also a good system and it will give you fairly good strong
signal
handling capability.

Pete

"Netgeek" wrote in message
...
Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

As a suggestion (too late if parts are incoming), a
single conversion to a 21.4 MHz IF is quite suitable.
Using a monolithic quartz crystal filter (available
from DigiKey for about $15 a pair of two) between
the mixer and first IF could eliminate ALL tuned
circuits in the IF following the 1st IF amplifier.
Those are available in 12.5 KHz bandwidth which will
be fine for a VOR signal. [DigiKey has a link to
download specs for the ECS-made monolithics]

This is now common in mobile radios, both new and
retrofit of older ones.

If a single-conversion scheme with 21.4 MHz is done,
the LO can be 86.6 to 96.6 MHz with an image at
65.2 to 75.2 MHz. That is a low enough frequency
to allow a simple L-C "top coupled resonator" fixed
bandpass filter for the front end at 108 to 118 MHz
(8.9 % bandwidth).

Doing double conversion with a first IF of 45 MHz
is, by itself, no problem. However the 2nd IF image
is a bit too close to the nominal bandwidth of any
45 MHz 1st IF tuning (it's only 0.91 MHz away). With
the second's image (on either side depending on 2nd
LO above or below 45 MHz), there's still a chance to
pick up part of the FM BC band locally. To avoid
that, the 2nd LO should be on the high side of 45.
Second IF image would then fall into the low end of
the 118 to 137 MHz comm band (also AM) and those
transmitters are much lower powered ones than BC
stations.

With a 10.7 MHz 2nd IF, its image would be 21.4 MHz
away and rather easy to attenuate in the 45 MHz 1st
IF. There's only a slight problem using stock
10.7 MHz IF components: Bandwidth of the whole 2nd
IF might be around 160 KHz; less discrimination to
nearby VORs and Localizers. A study of FAA sectional
charts might be called for to check on potential
interfering stations although those are assigned in
regards geographic locations to minimize normal
interference.

As a follow-up - I bought and assembled the really simple kit sold
by Ramsey - and described in detail he

www.sentex.ca/~mec1995/aviarx/avrxkitc.html

I wasn't expecting much - but was really surprised! It works really well
and has provided a platform that I can hack to death without feeling
bad about destroying it if it comes to that...

I'm about 8 miles from Washington National (DCA) with alot of "stuff"
in between. With a lousy 21" wire, I have no problems picking up both
Potomac Departure and Potomac Approach (with the first I heard being
Air Force One coming in to Andrews AFB).

The only modifications I've made are to increase the supply to 12V (from
9V - per Jim Weir's comments) and to replace the worthless 10k varactor
tuning pot with a 3-turn widget salvaged from some old Tektronix gear.

The thing works great!

Now I'm looking for suggestions on how to "improve" it. My list includes:

Replace NE 602 with SA612A mixer and add "real" tuning via National PLL
and Minicircuits VCO.

Replace 10.7 Mhz. ceramic filter with 4-pole Xtal-based filter.

Replace MC1350 with MC1349 (per Len Anderson) and rework AGC.

Add serious LP audio filter to output of AM detector diode.

Throw away or rework "squelch" circuit - as it is makes lots of noise and
is annoying (loud pops when switching in and out)...

Get a decent (e.g. dipole 1/2 wave antenna).

It seems to me that after attempting to improve the RF section the biggest
gains are to be had in tweaking the audio stages - so that's what I'm
focusing on. Just for fun - alot of filtering, noise gate, compression,
limiting, etc. seem to be areas where I can really play with the thing and
improve the performance. I've been looking at both Analog Devices
and THAT components as a step short of going to DSP. I think some
real improvements can be made. The basic signal is there (certainly at
levels which are "good enough") even with such a simple receiver. I'd
like to see what can actually be done (keeping in mind that this is a
"learning exercise"..)....

Any suggestions appreciated! (And, yes, there are plans to tweak the
IF per previous suggestions!)...

Thanks,
Bill

wrote in message
oups.com...
From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am

I would go directly from 45MHz to 455kHz..............this is typical
in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a
44.545MHz
crystal used with the on-board oscillator allows you to derive your
2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./
demodulator.
This is also a good system and it will give you fairly good strong
signal
handling capability.

Pete

"Netgeek" wrote in message
...
Parts are on the way...

First IF = 45 MHz
Second IF = 10.7 MHz

Any point in going further to 455 KHz for a third IF or just stick
with the 10.7 - (MC1350 plus IF transformer) scheme?

Bill

As a suggestion (too late if parts are incoming), a
single conversion to a 21.4 MHz IF is quite suitable.
Using a monolithic quartz crystal filter (available
from DigiKey for about $15 a pair of two) between
the mixer and first IF could eliminate ALL tuned
circuits in the IF following the 1st IF amplifier.
Those are available in 12.5 KHz bandwidth which will
be fine for a VOR signal. [DigiKey has a link to
download specs for the ECS-made monolithics]

This is now common in mobile radios, both new and
retrofit of older ones.

If a single-conversion scheme with 21.4 MHz is done,
the LO can be 86.6 to 96.6 MHz with an image at
65.2 to 75.2 MHz. That is a low enough frequency
to allow a simple L-C "top coupled resonator" fixed
bandpass filter for the front end at 108 to 118 MHz
(8.9 % bandwidth).

Doing double conversion with a first IF of 45 MHz
is, by itself, no problem. However the 2nd IF image
is a bit too close to the nominal bandwidth of any
45 MHz 1st IF tuning (it's only 0.91 MHz away). With
the second's image (on either side depending on 2nd
LO above or below 45 MHz), there's still a chance to
pick up part of the FM BC band locally. To avoid
that, the 2nd LO should be on the high side of 45.
Second IF image would then fall into the low end of
the 118 to 137 MHz comm band (also AM) and those
transmitters are much lower powered ones than BC
stations.

With a 10.7 MHz 2nd IF, its image would be 21.4 MHz
away and rather easy to attenuate in the 45 MHz 1st
IF. There's only a slight problem using stock
10.7 MHz IF components: Bandwidth of the whole 2nd
IF might be around 160 KHz; less discrimination to
nearby VORs and Localizers. A study of FAA sectional
charts might be called for to check on potential
interfering stations although those are assigned in
regards geographic locations to minimize normal
interference.

On Fri, 18 Mar 2005 06:36:33 GMT, "Pete KE9OA"
wrote:

I would go directly from 45MHz to 455kHz..............this is typical in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz
crystal used with the on-board oscillator allows you to derive your 2nd I.F.
Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator.
This is also a good system and it will give you fairly good strong signal
handling capability.

Pete

it is almost like the gunnplexer RX units we made around 1978-80,
wonder if the pcb's still exists for such receivers?

JM
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm