Two nearby ASOS broadcasts on the same frequency: Why no squeal?

[Peter R.]

For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
Wellsville, NY (KELZ), two small, uncontrolled airports in southwestern NY
state that are about 60 nm apart, share the same ASOS frequency.

For pilots flying to Dunkirk from the east, retrieving the current ASOS
broadcast is not possible until about 25nm east of the airport, due to the
more powerful KELZ broadcast. This is not so much a problem when
conditions are VFR, but when they are IFR I prefer to retrieve the ASOS as
early as possible in order to choose and prepare for a particular
instrument approach.

In any case, I am curious how it is possible for two transmissions to be
heard over an aviation frequency without the squeal (I forgot the
appropriate technical term for this).

--
Peter
























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[john smith]

Peter R. wrote:
> For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
> Wellsville, NY (KELZ), two small, uncontrolled airports in southwestern NY
> state that are about 60 nm apart, share the same ASOS frequency.

This is a classic situation to file a ASRS form.
Use this form to get action. It does work.

[JohnH]

Peter R. wrote:
> For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
> Wellsville, NY (KELZ), two small, uncontrolled airports in
> southwestern NY state that are about 60 nm apart, share the same ASOS
> frequency.
>
> For pilots flying to Dunkirk from the east, retrieving the current
> ASOS broadcast is not possible until about 25nm east of the airport,
> due to the more powerful KELZ broadcast. This is not so much a
> problem when conditions are VFR, but when they are IFR I prefer to
> retrieve the ASOS as early as possible in order to choose and prepare
> for a particular instrument approach.
>
> In any case, I am curious how it is possible for two transmissions to
> be heard over an aviation frequency without the squeal (I forgot the
> appropriate technical term for this).

They might just be lucky in that their transmitter oscillators happen to be
so closely matched that the beat frequency is subaudible. Good old AM
modulation! ;)

[Peter R.]

john smith > wrote:

> Peter R. wrote:
>> For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
>> Wellsville, NY (KELZ), two small, uncontrolled airports in southwestern NY
>> state that are about 60 nm apart, share the same ASOS frequency.
>
> This is a classic situation to file a ASRS form.
> Use this form to get action. It does work.

After five months of flying to Dunkirk every Monday, I am ashamed to admit
that it finally dawned on me last week to do this.

Interestingly, I asked Buffalo Approach, who controls approaches into
Dunkirk, if anyone else had complained that it is not possible to retrieve
the ASOS from the east until very close to the airport because of the
Wellsville ASOS sharing the same frequency. The controller responded that
no one had mentioned this before.

--
Peter






















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[Steven P. McNicoll]

"Peter R." > wrote in message
...
>
> For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
> Wellsville, NY (KELZ), two small, uncontrolled airports in southwestern NY
> state that are about 60 nm apart, share the same ASOS frequency.
>

What makes you think it's known only to the FAA? Whatever the reason, I
would expect it to be known to the FCC. In fact, it may be better known to
the FCC than the FAA.

It's probably because there isn't another suitable frequency available.

[Peter R.]

"Steven P. McNicoll" > wrote:

> What makes you think it's known only to the FAA? Whatever the reason, I
> would expect it to be known to the FCC. In fact, it may be better known to
> the FCC than the FAA.

Remember the time not so long ago when you used to post meaningful answers
to poster's legitimate questions? I recall a few years back when even I
received some genuinely helpful advice from you.

These days it seems you respond for no other reason than to exercise your
extremely dry and bland wit.

> It's probably because there isn't another suitable frequency available.

And why, assuming you can even take my question seriously, would there not
be a more suitable frequency available in a relatively quiet part of the US
(about 7 or so ASOS-equipped, uncontrolled airport in a 60nm mile radius)?

Of all the candidate ASOS frequencies (below 121.75 or so, perhaps?), what
would cause the FAA to choose the same one for two nearby airports?

--
Peter
























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[[email protected]]

>>>Of all the candidate ASOS frequencies (below 121.75 or so, perhaps?), what
would cause the FAA to choose the same one for two nearby airports? <<<

For that matter, why do Long Island's Easthampton and Montauk have the
same CTAF? (16nm apart) That's a real pain in the arse on a busy
weekend day... or under IFR... I know there are only so many freqs
available - maybe make MTP's PCL freq the CTAF? Just my .02

[Gene Seibel]

The frequency of the squeal is equal to the difference between the
carrier frequencies. Many of the TV transmitters I work with are now
required the be within +/- 3 Hz of their assigned frequency. We do that
by locking the oscillators to a reference derived from a GPS receiver.
They could easily be doing the same thing.
--
Gene Seibel KB0NNN
http://pad39a.com/gene/broadcast.html
Because I fly, I envy no one.

[kontiki]

When airports are really close together its a good thing to share
CTAF frequencies... so you know what's going on at each place because
the airspaces basically merge. You really appreciate the situational
awareness.

There is a point though, when traffic is very heavy that it becomes
detrimental.

wrote:

>>>>Of all the candidate ASOS frequencies (below 121.75 or so, perhaps?), what
>
> would cause the FAA to choose the same one for two nearby airports? <<<
>
> For that matter, why do Long Island's Easthampton and Montauk have the
> same CTAF? (16nm apart) That's a real pain in the arse on a busy
> weekend day... or under IFR... I know there are only so many freqs
> available - maybe make MTP's PCL freq the CTAF? Just my .02
>

[Neil Gould]

Recently, kontiki > posted:

> When airports are really close together its a good thing to share
> CTAF frequencies... so you know what's going on at each place because
> the airspaces basically merge. You really appreciate the situational
> awareness.
>
While that may be true of CFAF in some cases, it's not true of ASOS. For
example, in my vicinity there are 2 towered airports (as well as a Class B
and another Class D about 20 nm away in opposite directions). One ASOS is
located on a lake shore (600 ft. ASL) and another inland 10 nm away at 900
ft. ASL. The conditions at one is often not the same as the other. If both
ASOS were on the same frequency such that one steps on the other, it would
not be good.

Regards,

Neil

[Icebound]

"Peter R." > wrote in message
...
....
>
> In any case, I am curious how it is possible for two transmissions to be
> heard over an aviation frequency without the squeal (I forgot the
> appropriate technical term for this).
>


The "squeal" that you refer to, is the absolute difference in frequency
between the two base carriers of the two different transmitters. This
"difference" is known as the "beat" frequency. If the two base-carrier
frequencies are exactly correct, then the difference would be zero and no
"beat" sound would be produced. Today's equipment... it is normal to
maintain transmitter frequencies very, very accurate.

The human ear does not hear very well below about 20 hertz, so a tiny
difference of 5 or 10 hertz would not produce any "sound", either...
although it may manifest itself as a quick "pulsing" in the volume of the
signals as your receiver attempts to handle the interfering signals.

[[email protected]]

The squeal heard when two pilots key up on the same frequency is called
a heterodyne. I assume this is similar?

[RST Engineering]

Yes. The heterodyne effect occurs because both transmitters differ in
frequency by some audio tone. The allowable frequency error (from the
center of the design channel center) is +/- .003%. Assuming a transmitter
on 123.0 MHz. this means that one transmitter can be about 3700 Hz. (3.7
KHz.) high and one can be 3.7 kHz. low and still be within specification.
The beat note (heterodyne) between them is (3.7+3.7) 7.4 kHz. and this is
the tone you hear.

The odds of two radios being off to the limits at opposite ends of the
limits is very low; most of the heterodynes you hear will be in the 500-3000
Hz. range.

Having said that, since power consumption for a ground station is not a
primary concern, you can put the electronic device that controls frequency
into a temperature chamber (crystal oven) and expect that day in and day out
it will be within a few Hz. of where it was originally set. The same is
true of the other ground (ASOS) station, so the beat between them will be
very low and probably subaudible in an aviation headset. You may, if you
listen carefully hear a low rumble or (if they are very close) a wha-wha-wha
at one wha per second or so.

Wha is a technical term. You'll pick it up as you go along.

Jim



> wrote in message
oups.com...
> The squeal heard when two pilots key up on the same frequency is called
> a heterodyne. I assume this is similar?
>

[Ron Parsons]

In article >,
"Peter R." > wrote:

>For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
>Wellsville, NY (KELZ), two small, uncontrolled airports in southwestern NY
>state that are about 60 nm apart, share the same ASOS frequency.
>
>For pilots flying to Dunkirk from the east, retrieving the current ASOS
>broadcast is not possible until about 25nm east of the airport, due to the
>more powerful KELZ broadcast. This is not so much a problem when
>conditions are VFR, but when they are IFR I prefer to retrieve the ASOS as
>early as possible in order to choose and prepare for a particular
>instrument approach.
>
>In any case, I am curious how it is possible for two transmissions to be
>heard over an aviation frequency without the squeal (I forgot the
>appropriate technical term for this).

It's not unusual for a chain of transmitters to broadcast on what
appears to be the same frequency. They are actually all set about 5khz
apart and aviation radios filter out the squeal. That filter also makes
it more difficult to hear the higher pitched female voice.

[RST Engineering]

Say what? So far as I am aware, that is just not true.

Jim

"Ron Parsons" > wrote in message
...
>>
> It's not unusual for a chain of transmitters to broadcast on what
> appears to be the same frequency. They are actually all set about 5khz
> apart and aviation radios filter out the squeal. That filter also makes
> it more difficult to hear the higher pitched female voice.

[Dave Butler]

Ron Parsons wrote:
> That filter also makes
> it more difficult to hear the higher pitched female voice.

Where can I get one of those?

[john smith]

> Ron Parsons wrote:
>> That filter also makes it more difficult to hear the higher pitched
>> female voice.

Dave Butler wrote:
> Where can I get one of those?

Does it work on spouses and kids?

[RST Engineering]

You've got more than one spouse?

Jim




"john smith" > wrote in message
. ..
>> Ron Parsons wrote:
>>> That filter also makes it more difficult to hear the higher pitched
>>> female voice.
>
> Dave Butler wrote:
>> Where can I get one of those?
>
> Does it work on spouses and kids?

[Steven P. McNicoll]

"john smith" > wrote in message
. ..
>
> Does it work on spouses and kids?
>

If the plural of mouse is mice, why isn't the plural of spouse spice?

[Newps]

Dave Butler wrote:

> Ron Parsons wrote:
>
>> That filter also makes it more difficult to hear the higher pitched
>> female voice.
>
>
> Where can I get one of those?


Every man gets issued one at birth.

[Dave Stadt]

"Ron Parsons" > wrote in message
...
> In article >,
> "Peter R." > wrote:
>
> >For some reason known only to the FAA, both Dunkirk, NY (KDKK), and
> >Wellsville, NY (KELZ), two small, uncontrolled airports in southwestern
NY
> >state that are about 60 nm apart, share the same ASOS frequency.
> >
> >For pilots flying to Dunkirk from the east, retrieving the current ASOS
> >broadcast is not possible until about 25nm east of the airport, due to
the
> >more powerful KELZ broadcast. This is not so much a problem when
> >conditions are VFR, but when they are IFR I prefer to retrieve the ASOS
as
> >early as possible in order to choose and prepare for a particular
> >instrument approach.
> >
> >In any case, I am curious how it is possible for two transmissions to be
> >heard over an aviation frequency without the squeal (I forgot the
> >appropriate technical term for this).
>
> It's not unusual for a chain of transmitters to broadcast on what
> appears to be the same frequency. They are actually all set about 5khz
> apart and aviation radios filter out the squeal. That filter also makes
> it more difficult to hear the higher pitched female voice.

Guess every aviation radio I have ever used was broken 'cause they all
squeal. I think you need to review basic radio theory as it applies to our
dear old AM aviation radios.

[RST Engineering]

One sheriff, several sheraphim
One kleenex, several kleenesces
One moose, several meese

....we can keep going if you like {;-)


Jim



"Steven P. McNicoll" > wrote in message
nk.net...
>
> "john smith" > wrote in message
> . ..
>>
>> Does it work on spouses and kids?
>>
>
> If the plural of mouse is mice, why isn't the plural of spouse spice?
>

[George Patterson]

Steven P. McNicoll wrote:
>
> If the plural of mouse is mice, why isn't the plural of spouse spice?

It is. It gets *real* hot if you have more than one.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

[George Patterson]

Newps wrote:
>
> Dave Butler wrote:
>
>> Ron Parsons wrote:
>>
>>> That filter also makes it more difficult to hear the higher pitched
>>> female voice.
>>
>> Where can I get one of those?
>
> Every man gets issued one at birth.

The natural filter can be enhanced by extensive use of a rifle range without
hearing protection. In a pinch, a circular saw or a router will do the same, but
it takes longer.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

[W P Dixon]

For a Man,
The plural of spouse is ALIMONY ;)

Patrick
student SPL
aircraft structural mech

"George Patterson" > wrote in message
news:P1SKe.6112$lK2.3883@trndny01...
> Steven P. McNicoll wrote:
>>
>> If the plural of mouse is mice, why isn't the plural of spouse spice?
>
> It is. It gets *real* hot if you have more than one.
>
> George Patterson
> Give a person a fish and you feed him for a day; teach a person to
> use the Internet and he won't bother you for weeks.

[Morgans]

"RST Engineering" > wrote

> Having said that, since power consumption for a ground station is not a
> primary concern, you can put the electronic device that controls frequency
> into a temperature chamber (crystal oven) and expect that day in and day
out
> it will be within a few Hz. of where it was originally set.

Is this still commonly done today? What is a crystal oven, how big, and how
is the temperature regulated?

What? (wha) I (wha) can't (wha) hear (wha) you! (wha) <g>
--
Jim in NC

[RST Engineering]

The etymology of the word "alimony" is from the Latin, meaning to drag a
man's wallet out through his testicles.

Jim



"W P Dixon" > wrote in message
...
> For a Man,
> The plural of spouse is ALIMONY ;)

[Morgans]

"Dave Butler" > wrote
>
> Where can I get one of those?

Cut off your testicles, and start taking hormones.

Sorry gang, I typed it and hit send before I realized my alter ego did it.
<g>
--
Jim in NC

[RST Engineering]

Oh, it is common and fairly easy. You simply say, "the temperature here
will never exceed (some number say) 60d C. You then calculate the
parameters for the crystal oven for a fair margin of error (say, 65d C)

The crystal is about the size of two dimes held face to face. The oven is
about the size of four quarters held face to face with a cutout in the
middle to accept the crystal. On one side of the face of the quarters is a
fairly large resistor (1-5 watts) bonded with thermal epoxy to the face of
the outside quarter. On the opposite face is the temperature sensor,
similarly bonded to the quarter (thermistor or diode; I prefer diodes)

A controllable heater heats the resistor. When the temperature of the
quarters exceeds the temperature set of the thermistor/diode, the heater
shuts off. It is a bang-bang servo. There are a THOUSAND refinements that
you all can have.

>
> Is this still commonly done today? What is a crystal oven, how big, and
> how
> is the temperature regulated?


Jim

[Morgans]

"RST Engineering" > wrote

> Oh, it is common and fairly easy. You simply say, "the temperature here
> will never exceed (some number say) 60d C. You then calculate the
> parameters for the crystal oven for a fair margin of error (say, 65d C)

Who'uda thunk I'd learn something new today, when I got up? Not me, and not
here! <g>

Thanks! (I bet that makes yur life wurth liv'n) ;-))
--
Jim in NC

[Mike Money]

Spice spouse.
Steve, I always appreciated your candor, but humor too! You're the man.

[Steven P. McNicoll]

"George Patterson" > wrote in message
news:P1SKe.6112$lK2.3883@trndny01...
>
> It is. It gets *real* hot if you have more than one.
>

That's something that's always amazed me. I can understand why a guy gets
married the first time, he doesn't know any better. But after going through
the experience once some guys get married again. What the hell are they
thinking?

[George Patterson]

Steven P. McNicoll wrote:
>
> That's something that's always amazed me. I can understand why a guy gets
> married the first time, he doesn't know any better. But after going through
> the experience once some guys get married again. What the hell are they
> thinking?

I don't remember, but it seemed like a good idea at the time. :-)

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.