Firstly, 108 to 118 MHz is the international civil
aviation radionavigation band. It's not all that
interesting to listen to unless a local tower is
also repeating voice comms over a VOR or Localizer
radionav transmitter nearby on the ground. The
civil aviation voice band is 118 to 137 MHz.

Firstly, the tower does NOT repeat voice comms over a VOR. The local Flight
Service Station MIGHT, but in the days of crystal controlled navcoms, the
amount of voice traffic on a VOR is next to nothing.

Secondly, the tower/FSS will never in HELL repeat something on a localizer
frequency.

You are correct; the civilian aviation voice band is 118.000 to 136.975 MHz.



Jameco sells the MC145151 PLL IC (On Semiconductor
the Motorola spin-off still makes them) which, with
a prescaler, can make a good, stable LO that is
channelized at 50 KHz increments for precise tuning.
MC145151 is parallel-load for division, no extra
IC needed to get the right division ratio as in
some serial-input PLL or DDS chips.

The 145151 is OK if you don't mind spurs every 25 kHz. from dc to daylight.
The 145152 is a much better dual-modulo prescaler that gets rid of a lot of
trash and garbage from single modulo prescaling that you probably don't
want.

Jim

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

From: "RST Engineering" Mon, Mar 14 2005 8:11
pm

Firstly, 108 to 118 MHz is the international civil
aviation radionavigation band. It's not all that
interesting to listen to unless a local tower is
also repeating voice comms over a VOR or Localizer
radionav transmitter nearby on the ground. The
civil aviation voice band is 118 to 137 MHz.

Firstly, the tower does NOT repeat voice comms over a VOR. The local
Flight
Service Station MIGHT, but in the days of crystal controlled navcoms,
the
amount of voice traffic on a VOR is next to nothing.

Now, now, Jim. They do.

My residence is a mile and a half from BUR, roughly
eight miles from VNY here in the San Fernando Valley
area of Los Angeles.

Agreed, tower operators SELDOM repeat their transmissions
over the VOR but it is there in case it is needed. I've
heard them often enough.

VOR has an almost enormous bandwidth between 30 Hz and
the 9.96 KHz subcarrier phase reference...which was
INTENDED to carry voice as a conventience to the tower.

BUR, now the Bob Hope Airport, USED to carry the taped
weather broadcasts over their VOR but stopped several
years ago.

Secondly, the tower/FSS will never in HELL repeat something on a
localizer
frequency.

Calm down. I may still vote for you next election,
but not if you act like Arnie... :-)

Hokay, I may have spoken hastily on the voice over
Localizer. Color me "probably wrong" there.

You are correct; the civilian aviation voice band is 118.000 to
136.975 MHz.

Thank you. Sigh, I was only in the business of making
civil avionics and their test sets once. :-)

Jameco sells the MC145151 PLL IC (On Semiconductor
the Motorola spin-off still makes them) which, with
a prescaler, can make a good, stable LO that is
channelized at 50 KHz increments for precise tuning.
MC145151 is parallel-load for division, no extra
IC needed to get the right division ratio as in
some serial-input PLL or DDS chips.

The 145151 is OK if you don't mind spurs every 25 kHz. from dc to
daylight.

Sorry, I don't agree there. "Spurs" with an ordinary
PLL happen when the loop filter component values are
incorrect...and/or a higher frequency pole is used
(via an extra R and C in loop filter)to reduce higher
frequency components out of the PFD.

I've made a few PLLs with that MC145151 for homebrew
projects and not had any spurs from "DC to daylight"
or within the band of interest.

The 145152 is a much better dual-modulo prescaler that gets rid of a
lot of
trash and garbage from single modulo prescaling that you probably
don't
want.

I've not tried the 145152 but, back a number of years
before On Semi split from Motorola Semi, a Motorola
factory person said the 152 is essentially the same as
the 151 except for the serial data interface. I can't
vouch for that but that's what I remember.

Single modulus prescaling (putting a simple divide by
8 or divide by 10 in series with the VCO and PLL IC
signal input) doesn't produce any more #$%^&!!! stuff
than going direct into the PLL IC signal input. That
is said PROVIDED the loop filter output line to the
VCO it is controlling is "clean" and doesn't pick up
other circuit signals. Such garbage pickup is the
common cause of "spurs" and is layout dependent, NOT
dependent on whether or not any prescaling is done.
There's some dependency on proper supply rail decoupling
for the phase-frequency detector and any active op-amps
used between the loop filter and VCO control input.

By the way, I've used the MC1350 down to 10 V supply
rails with no problem although I do agree with it
running optimally (for gain and noise figure) at 12 V
supply. There's a lot of internal constant current
sources on that IC and that causes the dependency on
supply voltage. The same with the MC1349 which I'm
working with now as both gain blocks and as mixers.
I've worked with the MC1590 metal can original 34
years ago and the plastic package 1350 since 31 years
ago. I like it as a little block of gain which has
low distortion when running balanced input to balanced
output...on up to 70 MHz with hardly any gain rolloff.

On Sun, 13 Mar 2005 16:42:18 -0500, "Netgeek"
wrote:

I'd like to build some homebrew VHF-AM receivers - specifically a receiver
for the VHF 108-118 Mhz band.

Note that the FM broadcast band is just below that band with lot of
strong transmitters, so any configuration with low side local
oscillator injection and the more or less standard 10.7 MHz first IF
is most likely going to give image frequency problems from FM
broadcast stations in the 86.6 .. 96.6 MHz range. To avoid this, a
good narrow tunable filter is required in front of the first mixer,
which can be a problem if good frequency agility is required.

One approach would be to use a much larger first IF or put the local
oscillator above the desired band (which also swaps the sidebands)
with image responses in the rest of the aviation band.

One idea would be to use a fixed downconverter e.g. with a 98 MHz
crystal frequency, mixing the VOR band down to 10-20 MHz, filter out
the strong mixing products from the FM broadcast band that is on
frequencies below 10 MHz and use a DDS with I/Q outputs to get I/Q
demodulation of the signal.

Paul OH3LWR

wrote in message

Neither the range nor the accuracy of VORs is all that great on
the ground.

What do you intend to do with this doo-dad other than experiment if
I may ask?

For now it is strictly entertainment/education. If it works out, however,
I plan to use it as part of a complete FMS for something like this:

http://members.eaa.org/home/homebuil...ng%20flea.html

Good point about the range/accuracy on the ground - I'll do a special
version for Moeller and Bede products 8-).....

From: "Lawrence Statton N1GAK/XE2"

HAH! I did **EXACTLY** that project back in 1996 or so.
snip
Used a 68HC000 for the CPU, and had a database of VOR stations burned
into the ROM.
All in all it was a fun project -- with lots of cool learning
experiences.

Sounds like a cool project! *MANY* years ago (circa 1984 or so?)
I had a plan to tear off the front panel of an RST radio I built and
replace it with a display, some controls and a zillion parallel bits to
replace all the thumbwheels switches - all driven by a Z80. I
eventually decided it would take way too long and didn't
accomplish much, besides just being a generally stupid idea 8-)..
So I sold the radio...

Now, twenty years later I'm playing with *this* project! All of
which proves that I now have way too much time on my hands and
I'm getting more stupid as I age 8-)......

Would like to hear more about your experiences. So, what would
you do differently if you were starting over?

I'm thinking that something like a cheapo DSP (or one of the new
dsPIC widgets) might be real handy. But first - I have to get past
the part where I have a reasonable RF front end! I really doubt that
the $40 Ramsey kit is going to do much but I bet I'll learn a few
things 8-)........

"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-)

"Paul Keinanen" wrote in message

One idea would be to use a fixed downconverter e.g. with a 98 MHz
crystal frequency, mixing the VOR band down to 10-20 MHz, filter out
the strong mixing products from the FM broadcast band that is on
frequencies below 10 MHz and use a DDS with I/Q outputs to get I/Q
demodulation of the signal.

Thank you Paul - I'd like to look into this. Can you point me to some
practical examples or reference materials to start with? Quite some
time ago I ran across the articles from the flex-radio.com guys and
was very interested in their approach. 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?

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

From: "Netgeek" on Tues, Mar 15 2005 12:49 pm

"Paul Keinanen" wrote in message

One idea would be to use a fixed downconverter e.g. with a 98 MHz
crystal frequency, mixing the VOR band down to 10-20 MHz, filter out
the strong mixing products from the FM broadcast band that is on
frequencies below 10 MHz and use a DDS with I/Q outputs to get I/Q
demodulation of the signal.

Thank you Paul - I'd like to look into this. Can you point me to some
practical examples or reference materials to start with? Quite some
time ago I ran across the articles from the flex-radio.com guys and
was very interested in their approach. 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?

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.
Look into the allowed carrier tolerances and you will
see that, unless you can definitely LOCK onto the
incoming carrier, there will be a great change in the
modulation information, both in frequency and phase.

That is particularly true with VOR. The ground
station antenna pattern is (now) electronically
rotated at 30 Hz and the reference phase
(representing magnetic north) is FM on the 9 KHz
subcarrier. Without a proper phase relationship,
the bearing signal will be very inaccurate.

The VOR system was designed/innovated/invented over
a half century ago and was elegant in simplicity
for simple circuitry in vacuum-state hardware. The
first lightweight VOR receivers in light aircraft
used a (very old technology) small goniometer as
part of the OBS or Omni-Bearing Selector and their
accuracies were dependent on how well the goniometer
was designed and manufactured. [a goniometer is a
coaxial spherical toroid pair, best illustrated in
"Lowfer" or low frequency - below AM BC band -
small handbooks and some websites] More modern
versions use an electronic equivalent of phase
shifting at 30 Hz as part of the OBS subsystem.

A VOR antenna pattern rotation results in about
30% AM at a 30 Hz rate. The magnetic north phase
reference is 30 Hz FM on the 9960 KHz subcarrier.
The FM demodulation will have a limiter stage ahead
of it to effectively wash-out the 30% AM of the
ground station antenna pattern rotation. In
between the 30 Hz of the ground antenna pattern
rotation and about 8 KHz or so of the lower limit
of the 30 Hz FM on subcarrier phase reference is
"empty space" that was reserved for optional AM
from a local Flight Service Station (FSS) or tower
transmission. In short, the elegance of the
concept was ideally suited to vacuum tube circuitry,
that being an almost ultimate simplicity at the
time...and very light weight necessary for aircraft.

The "big bucks" of military electronics doesn't go
wild over fancy schmancy arrangements of the very
"in" modern complications. Those "big bucks" are
spent in making the hardware work over the totally
gargantuan range of temperatures and physical shock
and vibration that would tear apart consumer
electronics style structures. The civil avionics
market is not, nor has it ever been, large compared
to consumer electronics products, hence their costs
appear high.

There IS room for experimentation in ways to
demodulate the VOR information, don't get me wrong.
What you must do is to FIRST concentrate on the
characteristics of how the bearing information is
conveyed...along with all the problems introduced
by multi-path distortion from ground objects around
you. Those problems aren't there in the aircraft
flying a few thousand feet above all those reflecting
objects. [an exception is a VOR in a helicopter and
its own rotors...but that is another story in itself]

Just because the FM BC band upper end is at 108 MHz
doesn't automatically mean there WILL be RFI to the
receiver. That's a matter of checking a local area
to find where all those fixed FM BC carriers are and
how strong they are. Aircraft VOR receivers have
been overflying all sorts of FM BC stations for a
half century all over the world and there aren't
any stories (except invented horror tales) of terrible
interference from FM. Simpler civilian receivers,
not the "big bucks" of military aircraft.

Just offhand, I'd say a simple, even tube-based,
bearing information receiver can be hacked together
to get +/-5 degrees accuracy using the simplest
circuitry with minimum test equipment to check it out.
Anything better is just finesse, bottoming out at the
basic accuracy of whatever VOR ground station is used.
That would be +/-1 degree but worse from any ground
reception multi-path effects.

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...