DMEs are UHF, but you tune them in on a VHF frequency

Posted by 1E-12@reddit | flying | View on Reddit | 22 comments

From what I've gathered, every VOR frequency has a UHF pair so that you can dial in a DME (which is UHF) by tuning the VOR's VHF frequency. Does this mean that planes with a DME also have UHF receivers? When you tune "114.4 MHz" are you actually tuning in the UHF pair for that frequency? Or is the DME signal transmitted over VHF as well?

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22 Comments

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djd565@reddit

It’s on UHF. You are transmitting and receiving pulse pairs over the paired UHF channel.

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1E-12@reddit (OP)

Have to look for that antenna on my next preflight

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jaylw314@reddit

You probably figured this out long ago, but they can look EXACTLY like any other UHF antenna, such as your mode C antenna!

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Fancy_o_lucas@reddit

You may not have an antenna unless you have legitimate DME, GA almost exclusively use GPS as a substitute for DME now.

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Rocketsponge@reddit

Not all VORs have a paired DME freq. Check out the SSF VOR for an example of one, and the VOR 32 into KSSF for a VOR approach where the missed approach point is denoted by timing only.

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1E-12@reddit (OP)

Right I didn't mean to imply every VOR has a DME, only that every VOR frequency has a predetermined UHF frequency pair. That still sounds ambiguous... But I'm just saying the pair exists for reference, not that it is used at every transmitter.

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Apprehensive_Cost937@reddit

Yes. When you tune a VOR or an ILS frequency, an associated DME channel is tuned on the DME receiver automatically, and DME operates on UHF (around 1000 MHz mark). Even when you tune an ILS frequency (e.g. 110.10), only the localizer will transmit on this frequency. Glideslope signal will be at around 330 MHz, which is UHF. The aircraft have plenty of UHF receivers: DME, glideslope, SSR (transponder), GPS - they all use UHF, but that doesn't mean you could use those devices for UHF voice communication.

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1E-12@reddit (OP)

You read my mind regarding UHF comms. Where did you find the UHF pair for the VOR frequency?

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Apprehensive_Cost937@reddit

Check [this](https://europe1.discourse-cdn.com/flex013/uploads/navigraph1/original/3X/7/8/78c023517c479fb3af215af93d258e4907dd2c60.jpeg).

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jedensuscg@reddit

Except don't trust that fully. That is STANDARD frequency pairing, however there are VORTAC's or VOR/DME stations use nonstandard pairing, in which case you have to manually enter the DME or TACAN channel. Modern systems generally know the pairing in the database, even if it's not standard, but older systems would pair with a channel based on that pairing list, but then require manually changing the channel to match what it plates or charts said. THAT is the only accurate way to know what channel to pair with, they are listed on charts and approach plates.

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kmac6821@reddit

Sounds like Spangdahlem AB.

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indecision_killingme@reddit

Never seen non standard in civilian world. Most civilians don’t have access to the TACAN/VORTAC side of the VOR DME

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indecision_killingme@reddit

Similar table is in the AIM

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Frederf220@reddit

DME isn't actually on 114.4 MHz. It's *actually* 1114 MHz and 1051 MHz. The whole thing is channel 91X and that channel is several frequencies bundled together. There are known pairings of frequencies so it's possible to tune in a TACAN or DME using the VOR frequency as a cue even though there was no VOR service on that frequency. Your VOR equipment gets static but the DME gets DME service by virtue of being on the DME service frequency associated. You might not have been around then but DME equipment in the plane often had the ability to divorce the DME from the VOR frequency. The X and Y channel numbers also can refer to ILS or even MLS equipment. Like 18X is 108.1 ILS or rather includes 108.1 ILS in addition to other frequencies on that channel/bundle.

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cazzipropri@reddit

The UHF receiver is paired to the VHF one, and the two frequencies are paired via a fixed table. You dial one in, you get the second one for free without having to know it or dialing it in.

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jedensuscg@reddit

Sometimes it's for free, nonstandard pairings do exist, and that is why the channel is always listed next to the frequency on charts and plates.

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banditoitaliano@reddit

https://www.casa.gov.au/sites/default/files/2021-09/operational-notes-of-distance-measuring-equipment-dme-booklet.pdf Check this doc for technical details, particularly pages 2-2 and 2-3. Yes DME is exclusively using UHF so if you have a DME you have a UHF radio built in to that.

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1E-12@reddit (OP)

Thank you for the reference!

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jtyson1991@reddit

Yes, look at PilotsCafe page 13, the IFH page 9-17, or AIM 1-1-7.

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1E-12@reddit (OP)

Awesome - thanks for the refs!

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propell0r@reddit

Yes. The DME signal is transmitted over UHF to a specific DME transceiver on an aircraft. The transceiver will tune its UHF frequency by way of the VHF pairing you tune the associate NAV radio to. (Ie. DME 1’s UHF freq is tuned by whatever pairing is associated with the VOR frequency you put into NAV 1). Similar to how you tune a LOC, and the GS signal is tuned by automatic pairing.

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rFlyingTower@reddit

This is a copy of the original post body for posterity: --- From what I've gathered, every VOR frequency has a UHF pair so that you can dial in a DME (which is UHF) by tuning the VOR's VHF frequency. Does this mean that planes with a DME also have UHF receivers? When you tune "114.4 MHz" are you actually tuning in the UHF pair for that frequency? Or is the DME signal transmitted over VHF as well? --- Please downvote this comment until it collapses. Questions about this comment? [Please see this wiki post before contacting the mods](https://www.reddit.com/r/flying/wiki/index/rflyingtower/). --- I am a bot, and this action was performed automatically. If you have any questions, please [contact the mods of this subreddit](https://www.reddit.com/message/compose?to=/r/flying).