DME Audio IDENT Doesn't switch

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Oracle427
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Re: DME Audio IDENT Doesn't switch

Post by Oracle427 »

Original Q (asked by Dave): Then what is the purpose of the DME push button?
A: I assume you are referencing the button on the KMA-24? The answer is that it will allow you to listen to the DME ident audio.

Different Q: (asked by Rob): "With neither of the NAV audio buttons pushed and only the DME audio button activated, should the audio ID change from NAV 1 to NAV 2 within the DME audio system, when the DME info selector on the panel is changed from NAV 1 to NAV 2?" It does not...is that a bug or not?
A: This Bendix King manual does not appear to provide a clear answer to this question. https://www.bendixking.com/content/dam/ ... -guide.pdf
The DME system can only be tuned to one station at a time, therefore it must output the DME ident audio for currently turned station on the KDI 574 panel.

Hopefully this is precise enough for you now? I am unable to find an installation manual for the KDI574, but I honestly can't think of any other scenario that would make sense. None of the RW aircraft I have flown are equipped with DME and I rely on GPS in lieu of DME. I do not have practical experience with the matter of listening to DME audio to positively ident DME. I do not know if one would hear the DME audio for the station selected on the KDI 574 no matter which button is pressed for Nav 1 and Nav 2 on the KMA-24.

Based on what I have read from these manuals and the Avweb article, I would consider the scenario as described to be a bug.

Thinking about this a little further, I believe that the behavior should be modeled as follows for this specific installation.
1) Selecting NAV 1 on NAV 2 on the KMA-24 will only play the audio of the respectively tuned VOR
2) Selecting DME on the KMA-24 will only play the audio of the selected/held DME on the KDI-574
3) If a NAV source is selected and DME is not selected on the KMA-24, then no DME audio will be heard
4) If only the DME source is selected and both NAV sources are not selected on the KMA-24, then no NAV audio will be heard
5) If both a NAV source and DME is selected on the KMA-24, then both NAV and DME will be heard.
Flight Simmer since 1983. PP ASEL IR Tailwheel
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Nick - A2A
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Re: DME Audio IDENT Doesn't switch

Post by Nick - A2A »

Thanks for the posts here guys.

We've investigated and there is indeed a bug with the current implementation of the DME selector and audio panel in the V35B. As described by the OP, the DME morse ident for the NAV1 frequency is played if tuned, regardless of the position of the DME selector. We'll fix this behaviour with an update, although please bear in mind that the morse ident playback in frequency hold mode will most likely not be supported.

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Nick
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Oracle427
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Re: DME Audio IDENT Doesn't switch

Post by Oracle427 »

Is the change to stop the playback of the DME audio unless the DME button is selected on the KMA-24?
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Re: DME Audio IDENT Doesn't switch

Post by Nick - A2A »

The update will make the DME ident match whichever NAV frequency is selected via the DME selector. So, for example if the NAV1 and NAV2 radios are both tuned to separate VOR/DMEs, it will be possible to hear the NAV1 ident tone if the NAV1 ident button on the KMA 24 panel is depressed, along with the NAV2 DME ident tone if the DME selector is in the "N2" position.

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Nick
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Re: DME Audio IDENT Doesn't switch

Post by Oracle427 »

OK, that makes sense. Thanks!
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dsand2618
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Re: DME Audio IDENT Doesn't switch

Post by dsand2618 »

Thanks NICK. That is indeed he behavior that I expected. But with respect to the HLD position, if NAV1 and NAV2 are tuned to different frequencies and only the DME push button is depressed, what IDENT (if any) will be heard?

Dave

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Re: DME Audio IDENT Doesn't switch

Post by dsand2618 »

I failed to be clear. I mean when the HLD function is selected.

Dave

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Re: DME Audio IDENT Doesn't switch

Post by Oracle427 »

The audio is always going to be from the DME station that the DME system is locked onto.

DME is a completely separate system from the VOR/ILS stations that they are commonly, but not always paired with.

If one locks the DME system to a particular station using the hold function and then tunes the NAV radios to other VOR/ILSs, the DME system will continue to interact and receice from the locked DME station.

The audio heard from the DME stations is on a different frequency and received by a different antenna on the aircraft from that used by the NAV radios.

It is a matter of convenience that may be creating this confusion. The pairing of VOR/ILS and DME stations and their different frequencies is used to automate the tuning of the DME radio of the aircraft. It is a separate radio and one can only hear the audible ident audio signal when one presses the DME source, or equivalent, on their audio panel to permit that audio to be heard.

Prior to this standard of pairing VOR/ILS and DME frequencies, one would have had to manually tune the DME frequency in addition to the VOR/ILS frequencies which are not the same.

With automatic tuning one can have the impression that the audio is coming from a single source, when in fact it is not and what the pilot is hearing is the audio from multiple input channels.

Hope this helps to clarify what is happening under the covers. I also suggest a careful re-read of that Avweb article as it really does provide the insight into what is happening and will help you understand why these are the answers to the questions.
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dsand2618
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Re: DME Audio IDENT Doesn't switch

Post by dsand2618 »

I understand how it works in the real world. I am asking the developer what he meant when he said that the DME HLD function would not be supported. Will you hear nothing? Will you hear the Nav1 as you do now? Will you hear the last tuned DME? (As you should)

Dave

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Nick - A2A
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Re: DME Audio IDENT Doesn't switch

Post by Nick - A2A »

dsand2618 wrote: 21 Dec 2020, 21:08 I am asking the developer what he meant when he said that the DME HLD function would not be supported. Will you hear nothing?
Yes, that's what I meant.

Thanks,
Nick
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dsand2618
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Re: DME Audio IDENT Doesn't switch

Post by dsand2618 »

Thanks Nick.

Dave

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