Avidyne 550 vs Bendix/King Aeronav

[N201MKTurbo]

Just now, EricJ said:

Let me know if you want another set of eyes on it.  

I will, thanks.

[Baker Avionics]

11 hours ago, N201MKTurbo said:

It works fine, Cushman’s never go out of calibration. Besides, the problem isn’t with the signal generator, it is the radio.

Fair enough, so in your expert opinion, what caused this issue and why are most of the rest of the units produced working fine?  Further, in the STC installation as a singe radio, the Transmit interlock is not used, you are correct.  You will notice, by doing research that while it doesn't show in the manual it being hooked up, it also doesn't referenced being installed in a dual radio system especially with the KX155.  This issue is widely known in the Avionics Industry, at least in the places I have been and the ways I have been taught.  Several instances, especially with the KX155, it shows this problem and in every airframe, virtually.  You do not have to believe me and can try and discount this advice, that is fine and I have heard this rhetoric before.  That IS most likely the issue.  You are right, it will not matter which radio is installed, but instead of discounting the advice, try installing that line, as it should be, and then try it. you will be happy with the results.  I really don't care what the bench test equipment says. I've been doing this way too long from big iron to part 23.  It is what it is.  I want to let everyone know that this is not in haste or with any bad emotion, I am as cool as the other side of the pillow on this.  I just want to help.  

[Marauder]

1 hour ago, Baker Avionics said:

Fair enough, so in your expert opinion, what caused this issue and why are most of the rest of the units produced working fine?  Further, in the STC installation as a singe radio, the Transmit interlock is not used, you are correct.  You will notice, by doing research that while it doesn't show in the manual it being hooked up, it also doesn't referenced being installed in a dual radio system especially with the KX155.  This issue is widely known in the Avionics Industry, at least in the places I have been and the ways I have been taught.  Several instances, especially with the KX155, it shows this problem and in every airframe, virtually.  You do not have to believe me and can try and discount this advice, that is fine and I have heard this rhetoric before.  That IS most likely the issue.  You are right, it will not matter which radio is installed, but instead of discounting the advice, try installing that line, as it should be, and then try it. you will be happy with the results.  I really don't care what the bench test equipment says. I've been doing this way too long from big iron to part 23.  It is what it is.  I want to let everyone know that this is not in haste or with any bad emotion, I am as cool as the other side of the pillow on this.  I just want to help.  

Is that your picture on your website? If so, why is it all avionics guys are completely bald or have shaved heads? 

It is unfortunate that many of these avionics tidbits need to be learned through experience rather than by documentation. I know Garmin has a pretty extensive service bulletin process that keeps shops informed. Is Avidyne in the same category of managing these things or do they leave this stuff up to tribal knowledge?

[N201MKTurbo]

1 hour ago, Baker Avionics said:

Fair enough, so in your expert opinion, what caused this issue and why are most of the rest of the units produced working fine?  Further, in the STC installation as a singe radio, the Transmit interlock is not used, you are correct.  You will notice, by doing research that while it doesn't show in the manual it being hooked up, it also doesn't referenced being installed in a dual radio system especially with the KX155.  This issue is widely known in the Avionics Industry, at least in the places I have been and the ways I have been taught.  Several instances, especially with the KX155, it shows this problem and in every airframe, virtually.  You do not have to believe me and can try and discount this advice, that is fine and I have heard this rhetoric before.  That IS most likely the issue.  You are right, it will not matter which radio is installed, but instead of discounting the advice, try installing that line, as it should be, and then try it. you will be happy with the results.  I really don't care what the bench test equipment says. I've been doing this way too long from big iron to part 23.  It is what it is.  I want to let everyone know that this is not in haste or with any bad emotion, I am as cool as the other side of the pillow on this.  I just want to help.  

I'm not trying to discount your advice, but there is no information in the install manual that indicates that it is doing anything at all. I have to assume from the note (Unused) that that signal is indeed not used in the Avidyne. I assume that signal is listed because it is used in the Garmin 530 and Avidyne being pin compatible with the Garmin just listed it for reference. 

Can you point me to any other reference material that indicates that it is used in the 550?

[Baker Avionics]

3 minutes ago, Marauder said:

Is that your picture on your website? If so, why is it all avionics guys are completely bald or have shaved heads? 

It is unfortunate that many of these avionics tidbits need to be learned through experience rather than by documentation. I know Garmin has a pretty extensive service bulletin process that keeps shops informed. Is Avidyne in the same category of managing these things or do they leave this stuff up to tribal knowledge?

Hahaha!  Yup, guilty!  Most of my lack of hair comes from kids, marriage and trainees.  LOL.  Garmin addresses a lot via SB processes that are mainly founded by and from tribal knowledge, to be honest.  Avidyne is the same.  However, most of the time it is about understanding HOW things work over time and WHY things are there.  Mark, a good friend for many years (PS Engineering), has many references about "Transmit Interlock" connections and why they are necessary.  People can rely on manuals but they are JUST guidance and not the Bible for the units.  They are strictly a depiction of what the certification hook ups were.  Common sense and experience has a lot to do with the industry not to mention Avionics.  People, these days, try and use the "book knowledge" to their advantage when really, it is, like the FARs, guidance.  As Lt. Sam Weinberg states in A Few Good Men:

 

you keep after the way you did suddenly our great cross looks like a bunch of fancy lawyer tricks, there's a difference between paper law and trial law

The same applies here.  There is a difference between the basic hookups and how it should be in the real world.  We tell the kids who come out of A&P School and the military the same thing.  Everything you have read in the manuals and learned in school, forget, figuratively, this is where you learn and figure out how things REALLY work.

[Baker Avionics]

7 minutes ago, N201MKTurbo said:

I'm not trying to discount your advice, but there is no information in the install manual that indicates that it is doing anything at all. I have to assume from the note (Unused) that that signal is indeed not used in the Avidyne. I assume that signal is listed because it is used in the Garmin 530 and Avidyne being pin compatible with the Garmin just listed it for reference. 

Can you point me to any other reference material that indicates that it is used in the 550?

I totally understand where you are coming form and just want to help.  I will try and find the justification, but part of it is just experience.

[tmo]

Excuse my ignorance, but a quick search didn't turn anything useful up - how is the transmit interlock supposed to be connected?  I have a GNS430 on which I sometimes hear a garbled version of what my KY197 is transmitting, so perhaps I too am missing a wire...

Thanks!

[EricJ]

On 12/23/2019 at 11:40 AM, N201MKTurbo said:

I’ve done all that. The interference goes away when I power down the Avidyne. The Avidyne makes the KX155 unusable on 119.4 also.

I took my signal generator and spectrum analyzer to the hangar today, and hooked them up so that I could send the same signal through a splitter to both the IFD540 and my TKM MX170C at the same time.   The signal feeding that splitter was split from the signal generator to also feed the spectrum analyzer to calibrate output power.   I checked fourteen different frequencies from 118.4 up to 133.725, including 119.4 and did not find any significant frequency dependence.   For the most part my IFD breaks auto-squelch at around -97 dBm (3.1 uV) and if you defeat the squelch you can hear the signal down to about -104dBm (1.4 uV).    The TKM breaks squelch pretty consistently at about -87dBm (10 uV) and if you defeat the squelch with the "test" button you can hear the signals pretty well down past about -105 dBm (1.26 uV).   The squelch on the TKM is adjustable, so I should probably crank that down a bit as it appears to just be adjusted quite high.    Otherwise those sensitivity levels are more or less what I would expect for an AM voice radio.  Digital stuff I've worked on these days can get down to -115 to -120 dBm or better, but that's a pretty serious radio with some significant processing gain.

So other than the squelch being a bit misadjusted on the TKM, they're reasonably similar, with the TKM being more sensitive, and neither showed any significant frequency dependence or issues around 119.4 MHz, and I had the entire panel on for all of the testing.   This was in my hangar with everything powered by my GPU.   The audio filtering on the TKM appears to maybe be a little better, or at least the audio AGC, as it was easier to hear a small signal on it than on the IFD, mostly because the IFD was amplifying the background noise more.   The IFD was more annoying with a small signal with the squelch defeated, but I could still hear the signal at the levels indicated.

I also put a sniffer antenna up next to both of my 7 antennas with the radios on and they're both clean, i.e., no local oscillator spurs coming out when tuned to 119.4, which is one way that tuners have frequency-specific problems.   I also put the antenna up behind the radios under the panel, and while there's fair amount of crap radiated back there (as expected), there was nothing notable at 119.4 anywhere, even near the IFD.   I don't have a good DC block fitting right now that I trust well enough to protect my spectrum analyzer, or I'd have looked at whether there was any suspicious noise on the power supplies.   Since the sensitivities don't appear to be problematic on mine and there doesn't seem to be any frequency dependence, there's no smocking gun to look for there, anyway.  

This suggests that the issues you're experiencing probably aren't endemic to IFDs, but may be due to an issue with your particular radio or installation. 

Anyway, since I have an IFD540 I thought it would be worth checking.   Since yours in an IFD550 there may be a possibility that the AHRS is generating interference, but who knows.

Just wanted to pass it along.   Not very helpful, but it's something.

 

Edited December 27, 2019 by EricJ

[N201MKTurbo]

1 hour ago, EricJ said:

Just wanted to pass it along.   Not very helpful, but it's something.

I’ve thought it was my install, and the other guy’s too, just can’t figure out what it is. The grounding seems proper. I’ve replaced the coax, I’ve changed antennas, swapped the coax between the front and back antennas, nothing has made it go away. 

I put the 550 in another plane and it didn’t have the problem. I put a 530 Garmin in my plane and it worked perfect. (Troy offered to make an even swap). I wish it would just go away.

If you are available Saturday we could get together and see what we can see.

[EricJ]

4 minutes ago, N201MKTurbo said:

I’ve thought it was my install, and the other guy’s too, just can’t figure out what it is. The grounding seems proper. I’ve replaced the coax, I’ve changed antennas, swapped the coax between the front and back antennas, nothing has made it go away. 

I put the 550 in another plane and it didn’t have the problem. I put a 530 Garmin in my plane and it worked perfect. (Troy offered to make an even swap). I wish it would just go away.

If you are available Saturday we could get together and see what we can see.

Can definitely do that.   Let me know when.   Might drive down instead of fly, or you can fly up, either way.

[bradp]

On 12/24/2019 at 12:52 PM, Baker Avionics said:

I totally understand where you are coming form and just want to help.  I will try and find the justification, but part of it is just experience.

@Baker Avionics @Mscheuer

Doesn’t transmit interlock need to be disabled for certain PS engineering split com functions? 
 

Woul proper antenna farming / placement be the first defense against dual com transmission bleeding over? 
 

thanks and take care

brad