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"?)...!

wrote in message

Direct conversion (DC) won't be effective on this
application for reasons of the civil aviation band
being AM with no pilot carrier or other reference.

SNIP - [lots of good information]

VOR (Very high frequency Omnidirectional radio Range)
was designed only for aircraft obtaining bearing
information to a fixed ground station. That's a
limited application although extremely important to
pilots. A half century ago it was a quantum leap
above older raw-DF-style radionavigation. GPS it
ain't, nor never was...



Well, that was certainly a very informative and well thought
out response! But GEEZ, Len, you're starting to take all the
fun out of this by insisting on injecting reality!!!....8-)

Here I was - with soldering iron warmed up and pile of odd
looking components (SA-614, MC1350, NE567, inductors,
IF transformers and all kinds of other "stuff" that's unfamiliar)
and now my hopes are dashed............

I even checked Mouser, Digikey et. al. - and they're fresh out
of goniometers - so there goes *that* approach...8-(

But seriously - let's look at the potential utility of a fairly "mindless"
NAV receiver as it might apply to the non-instrumented-rated,
day-VFR "Sport" or "Recreational" pilot. First off, these guys
believe that GPS coupled to a simple moving map display represents
not only the holy grail - but they'd be willing (foolishly) to bet their
lives on this sole-source nav capability (never mind simple "dead
reckoning" or other elementary - e.g. "follow roads" forms of
navigation). If the batteries run out on the GPS - or the guys at
Cheyenne Mountain pull the big red lever marked "scramble GPS"
for whatever reason - they're in big trouble. Standard VOR-based
equipment would give them a way out - but they don't have it ('cause
it costs too much) and they wouldn't know how to effectively use it
anyway ('cause they aren't instrument rated). Some form of relatively
simple (albeit far from accurate) NAV capability would at least give
them a last chance to drag out the sectional and try to determine roughly
where they are - hopefully close enough to find a place to put down.

My ridiculous little experimental project is to try and come up with a
"poor man's" (and perhaps "stupid man's 8-) nav capability based on
VORs which is inexpensive and SIMPLE. There's no OBS nor any
other "normal" features (e.g. ability to drive a CDI) - but it kicks out
enough info relative to a few nearby VORs so that you can at least
determine what planet you're on 8-).... and provide a few hints as to
*where* you are on that planet...

GPS replacement? Absolutely not. TSO'd NAV receiver replacement?
Nope - not that either. Inexpensive (enough so that you might actually
install one) and simple (enough so that you could derive some useful info
with little training) - that would be the goal.

In the meantime, it's really a personal educational and entertainment
toy to play with, and nothing more ("amateur", "homebrew", etc. - so
it's relevent here, right?)......8-)

I appreciate your thoughts and comments, Len! You obviously have a
wealth of experience to draw upon and I thank you for sharing it. Despite
more than 25 years in product development, most of this is new territory
for me (and I'm enjoying the learning experience!). I've never done an
RF design - well - at least not "deliberately"!!!

Regards,
Bill

Netgeek wrote:

snip

But seriously - let's look at the potential utility of a fairly "mindless"
NAV receiver as it might apply to the non-instrumented-rated,
day-VFR "Sport" or "Recreational" pilot. First off, these guys
believe that GPS coupled to a simple moving map display represents
not only the holy grail - but they'd be willing (foolishly) to bet their
lives on this sole-source nav capability (never mind simple "dead
reckoning" or other elementary - e.g. "follow roads" forms of
navigation). If the batteries run out on the GPS - or the guys at
Cheyenne Mountain pull the big red lever marked "scramble GPS"
for whatever reason - they're in big trouble.

If that happened, and that's a pretty big if given the US government
is forcing GPS as the defacto navigation standard for just about
everything, the accuracy would be reduced to such that it would be
impossible to make a precision approach.

The remaining accuracy would be more than enough to find an airport,
especially since Sport and Recreational are limited to day VFR.

Standard VOR-based
equipment would give them a way out - but they don't have it ('cause
it costs too much) and they wouldn't know how to effectively use it
anyway ('cause they aren't instrument rated). Some form of relatively
simple (albeit far from accurate) NAV capability would at least give
them a last chance to drag out the sectional and try to determine roughly
where they are - hopefully close enough to find a place to put down.

Sporty's sells the SP-200 NAV/COM handheld for $299.00 with a $14.95
rebate if you use your AOPA credit card. It has VOR and LOC with a
digital CDI display and 2,280 channel COM. You still would have to
know what 235 FROM means.

IMHO anyone not flying a big turbine with multiple redundent everything
that doesn't have a handheld just in case is foolish.

My ridiculous little experimental project is to try and come up with a
"poor man's" (and perhaps "stupid man's 8-) nav capability based on
VORs which is inexpensive and SIMPLE. There's no OBS nor any
other "normal" features (e.g. ability to drive a CDI) - but it kicks out
enough info relative to a few nearby VORs so that you can at least
determine what planet you're on 8-).... and provide a few hints as to
*where* you are on that planet...

GPS replacement? Absolutely not. TSO'd NAV receiver replacement?
Nope - not that either. Inexpensive (enough so that you might actually
install one) and simple (enough so that you could derive some useful info
with little training) - that would be the goal.

In the meantime, it's really a personal educational and entertainment
toy to play with, and nothing more ("amateur", "homebrew", etc. - so
it's relevent here, right?)......8-)

I appreciate your thoughts and comments, Len! You obviously have a
wealth of experience to draw upon and I thank you for sharing it. Despite
more than 25 years in product development, most of this is new territory
for me (and I'm enjoying the learning experience!). I've never done an
RF design - well - at least not "deliberately"!!!

Regards,
Bill

Decoding the bearing can be done with a PLL running as a 360X frequency
multiplier on one 30 Hz signal and using the other to gate a counter
which is feed the multiplied signal.

I built such a beast in '75 as a senior project with a NIXIE tube
display. Available compenents have improved a lot since '75.

If I were to do something like this today, I think I would look for
someone's receiver module and use a microcontroller to control the
receiver and do most (maybe all with DSP) the decoding, feeding it all
to a PDA with a database of VOR frequencies and locations and use the PDA
to generate a map display.

It would be a fun project.

--
Jim Pennino

Remove -spam-sux to reply.

On 16 Mar 2005 12:58:44 -0800, wrote:

Direct conversion (DC) won't be effective on this
application for reasons of the civil aviation band
being AM with no pilot carrier or other reference.

If you are running an I/Q DDS feeding I and Q demodulators (mixers)
and low-pass filter the quadrature demodulator, producing a DC voltage
proportional to the phase error. This could be used through an ADC to
control the phase modulator input (or the phase accumulator addend) of
the DDS to track the signal. However, DDS chips with only serial input
might be too slow to track the signal. The I demodulator output would
provide the amplitude modulated information.

Paul OH3LWR

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"?)...!

The Mini-Circuits SRA-2H comes to mind...............Level 17, which
requires 50mW of LO injection.

Pete

"Paul Keinanen" wrote in message
...
On Tue, 15 Mar 2005 12:49:01 -0500, "Netgeek"
wrote:

It's my understanding (and I
mean a fairly fuzzy understanding) that direct conversion has many
benefits but is limited to lower bands (unless you're the military with
a big budget)??? What are the trade-offs in doing a downconversion
followed by DDS-based conversion?

My suggestion of using a DDS for direct conversion in the 10-20 MHz
range is based on the assumption that DDS chips running with 50-60 MHz
clock frequency should be available at a quite a reasonable price,
compared to similar chips running at 400 - 500 MHz, which would be
required for direct synthesis in the VHF band.

However, translating the whole band down to HF requires a strong down
converter, especially due to the nearby strong signal broadcast band.
Some flimsy NE602 type converter will not survive very well in such
environment, but a high current preamplifier followed by a diode ring
mixer might be a better converter.

Paul OH3LWR

"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.

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