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When flying in beautiful VFR weather, I often search for a quiet frequency so I don't listen to a lot of chatter.

Guard (121.5) sometimes works, but sometimes has "Guard"-ians on it.
("Yer on gaaard")

Many frequencies end up being a distant CTAF that have garbled transmissions.

Short of turning my radio completely off, is there a frequency within the US (or even an ARTCC) that will always be silent, but can easily swap back to a working frequency?

Some have suggested just turning the volume down and back up. That is functional, but not quite as easy as pressing the XFER button, since the volume may be too loud or too soft after adjusting it.

I like the idea of trying the low-power frequencies that I'm less likely to hear; but I am ultimately hoping to learn of a frequency marked "do not transmit on".

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    $\begingroup$ Uhm .. turn down the volume of your radio? $\endgroup$
    – 60levelchange
    Commented Sep 25, 2017 at 16:25
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    $\begingroup$ You mean you don't always monitor 121.5 as required by NOTAM? ;-) $\endgroup$
    – Pondlife
    Commented Sep 25, 2017 at 16:34
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    $\begingroup$ A frequency marked 'do not transmit on' made me think of a sign I saw once on a door, which said This door must remain closed at all times. I wondered "Then why have a door there?" $\endgroup$
    – Steve V.
    Commented Sep 26, 2017 at 3:53
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    $\begingroup$ I have down-voted this question because I feel it is poor airmanship to intentionally remove the possibility of communicating with another aircraft or ground facility. $\endgroup$
    – Mike Sowsun
    Commented Sep 26, 2017 at 14:45
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    $\begingroup$ I consider that an inappropriate downvote: There is nothing wrong with the question, you just don't like idea; but downvotes are for literally bad questions. There are plenty of cases where it is appropriate to have a quiet cockpit; During flight instruction, it is common for the instructor to silence the radio for the student's benefit. $\endgroup$
    – abelenky
    Commented Sep 26, 2017 at 14:49

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From the document referenced by mongo,

Frequencies (MHz): 121.425 - 121.475
Use: Band Protection for 121.5

Frequencies (MHz): 121.525 - 121.575
Use: Band Protection for 121.5

It seems that these frequencies exist only to be silent space around Guard/121.5.

No one should transmit on them, and you should probably hear total silence there.

I think these are an excellent place to look for quiet space.

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You might want to check out this list of assigned frequencies. These look like good bets.

136.100 Reserved for future unicom or automatic weather observation stations

122.975 Unicom (high altitude)/U.S. Forest Service air operations

123.125 U.S. Air Force NAVAID flight check/NASA T-38 Interplane Nationwide

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  • $\begingroup$ @mongo I think that the list is just copied from the AC you referred to below. The AC is the more definitive source. $\endgroup$
    – JScarry
    Commented Sep 25, 2017 at 21:57
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I'd try 121.1 to 121.4. I am not aware of them having been assigned for routine use. There's no guarantee that an unassigned frequency won't be in use by someone, authorized or not.

Use of frequencies between 121 and 122 are typically limited to 'low power' or other restricted applications to avoid adjacent channel interference with Guard. This is why ground control frequencies are normally between 121.6 and 121.9.

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  • $\begingroup$ KAVL's CTAF is 121.1 $\endgroup$
    – Steve Kuo
    Commented Sep 25, 2017 at 17:33
  • $\begingroup$ @SteveKuo I'm not surprised. There are exceptions. Frequency assignment is a complicated engineering process. There are guidelines, but sometimes there has to be an exception. If you're looking for more info, try the FAA Spectrum Plan or Regs and Procedures. $\endgroup$
    – Gerry
    Commented Sep 25, 2017 at 18:48
  • $\begingroup$ Using that Spectrum Plan as a guide, I found that 121.7750 is for Search and Rescue Practice on ELTs, so is probably pretty unlikely to hear anything there. I'll try that frequency for awhile, and see if that is accurate. $\endgroup$
    – abelenky
    Commented Sep 25, 2017 at 19:56
  • $\begingroup$ @Gerry is correct about guard, in that it is given a 100kHz protection around 121.5. $\endgroup$
    – mongo
    Commented Sep 25, 2017 at 21:24
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    $\begingroup$ @Gerry I think the point of GND frequencies is that they are generally used on the ground, which limits their radiated area. The need for 121.5 near the airport remains the same as elsewhere, but 121.5 is given 100 kHz spacing. I don't have a modern transceiver rejection for 100 kHz off, but it's probably something like -95 to -105db. It is that rejection which protects 121.5. $\endgroup$
    – mongo
    Commented Sep 28, 2017 at 0:39
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The FCC publishes the frequency assignments for aeronautical radio usage (Part 87). You may wish to "listen" anywhere, but technically one should be monitoring guard when a receiver is available.

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC90-50D.pdf

https://www.gpo.gov/fdsys/pkg/CFR-2016-title47-vol5/xml/CFR-2016-title47-vol5-sec87-173.xml

Addendum #1 Protected frequencies, such as around guard, are implemented as "channels" which are effectively wider. From a practical standpoint, this allows "weaker" signals to be heard without splatter or bleed over from adjacent channels. In the case of guard, a time honored technique is to tune a radio off channel, and use that as a metric of how strong a signal is. This is helpful if flying a grid, looking for an ELT, as an example. I have never been in CAP, but I have located several downed aircraft, and participated in one manner or another of helping locate perhaps dozens of others over the years. If you want to practice the technique, you can use some continuous transmitter, such as AWOS. Newer radios have better off channel rejection than some of the radios which have been retired in recent years because they did not accommodate current channelization. So this technique may not yield the same information about the strength that an oder radio might. Nonetheless, knowledge of this method may prove helpful at some time.

And about all those downed aircraft? A large number of them were not crashes but rather planes tied down, and where no one apparently listened on 121.5 after that last hard landing. Higher flying aircraft would pick up an ELT, and advise center or in ancient times, FSS. They in turn would request aircraft in the vicinity to report whether they heard an ELT, and create a most probable map of where the ELT was. Most of the time, would find ELTs at night sitting on the ground at an unlit grass field, with a mercury vapor light nearby, lighting the aircraft.

Addendum #2: To answer the OP question more directly, tune to 121.475. If you hear anything there, you might go to 121.5 because there is likely a strong signal on 121.5. It could be a downed aircraft in your vicinity, or it could be a plane intercepting you, or something else possibly worthy of your attention. But this adjacent channel should be quiet most of the time, and should satisfy your need for a quiet frequency.

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