N201MKTurbo Posted August 13, 2018 Report Share Posted August 13, 2018 The last time I flew to Cali a couple of weeks ago the Avidyne would not change to VLOC on the ILS and I had to complete the approach using the KX155. I figured I was doing something wrong. On a flight the other day I just tried to dial up a few VORs on the 550 and it wouldn't pick up any of them. So the NAV receiver wasn't working. I dusted off my old Cushman CE50A service monitor from the garage and took it to the hangar. I fired it up and confirmed that it was mostly working. I set it to 113.7 with a 5Khz tone at 50% and max output with an ELT antenna hooked to it. I could hear a solid quiet tone on the KX155 and a very weak and noisy signal on the Avidyne. Next I ran a cable from the generator to the antenna input on the NAV splitter. I could detect the signal on the KX155 at 0.5uv and it quieted to ~20db SINAD at 1.5uv. This is quite good. With the Avidyne I could detect the signal at 3mv and it got quiet at about 5mv. So the Avidyne was about 2000 times weaker then the KX155. Next I connected the generator directly to the Avidyne which caused my arm to bleed from a wayward ty-wrap tail. It was much better! I could detect the signal at 3uv and it quieted at 6uv. So it must be the splitter or the cable from the splitter to the radio. I replaced the cables and re-connected the generator to the splitter. Now I was getting the same performance as when jacked directly into the radio. No amount of connecting and disconnecting or bending the cables would make it quit! Stupid cables... I was still concerned that the sensitivity of the Avidyne was about 4 times worse than the KX155. I opened the install manual for the Avidyne and looked at the specs for the NAV receiver. It says the NAV flag will go off at 10uv. That is a pretty crappy spec. In reality it is quieting at ~6uv so it is performing better than its spec. The bottom line is the Avidyne has a crappy NAV receiver. But then again it is advertised as a GPSCOM not a NAVCOM. Just some radio porn for you radio geeks. 1 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 13, 2018 Report Share Posted August 13, 2018 Rich, Did it stop working over time, or never quite worked from the beginning? @Piloto is pretty good with Antenna and receiving ideas... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 13, 2018 Author Report Share Posted August 13, 2018 It worked great until I noticed that it didn't work at all. 1 Quote Link to comment Share on other sites More sharing options...
jackn Posted August 13, 2018 Report Share Posted August 13, 2018 You have some nice toys! Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 13, 2018 Author Report Share Posted August 13, 2018 3 minutes ago, jackn said: You have some nice toys! My wife likes to classify them as junk! Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 13, 2018 Report Share Posted August 13, 2018 Looks like the NAV rx spec for the KX155 is 1/2 flag at 2uV, so, yeah, the spec and/or performance for the IFD apparently aren't as good. Garmin apparently publishes their specs in dBm, which makes a lot more sense to me but isn't comparable. Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 13, 2018 Author Report Share Posted August 13, 2018 7 minutes ago, EricJ said: Looks like the NAV rx spec for the KX155 is 1/2 flag at 2uV, so, yeah, the spec and/or performance for the IFD apparently aren't as good. Garmin apparently publishes their specs in dBm, which makes a lot more sense to me but isn't comparable. 2uv = -101DBm Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 13, 2018 Report Share Posted August 13, 2018 (edited) 6 minutes ago, N201MKTurbo said: 2uv = -101DBm It depends on the active impedance in the receiver, so it's never really 100% comparable. Not that the specs are ever really accurately comparable even if they're in the same units, but, still. The GNS530 VOR receiver sensitivity spec is -103.5 dBm. I couldn't find a specc for the GTN units, maybe that means they're not great, either. My TKM specs 1/2 flag at 1.5uV, and seems to pick stuff up about the same time as the IFD540. I was expecting the IFD to be a bit more sensitive, and sometimes it is and sometimes it isn't. I'm in SoDak now and will compare them some more on the way back now that there's a reason to play with them. Edited August 13, 2018 by EricJ Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 13, 2018 Author Report Share Posted August 13, 2018 7 minutes ago, EricJ said: It depends on the active impedance in the receiver, so it's never really 100% comparable. Not that the specs are ever really accurately comparable even if they're in the same units, but, still. The GNS530 VOR receiver sensitivity spec is -103.5 dBm. I couldn't find a specc for the GTN units, maybe that means they're not great, either. My TKM specs 1/2 flag at 1.5uV, and seems to pick stuff up about the same time as the IFD540. I was expecting the IFD to be a bit more sensitive, and sometimes it is and sometimes it isn't. I'm in SoDak now and will compare them some more on the way back now that there's a reason to play with them. That was assuming 50 Ohms of course. Watts, volts what ever... It looks like we are all in the same ball park. I'm anxious to see your data. 1 Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 13, 2018 Report Share Posted August 13, 2018 Just now, N201MKTurbo said: That was assuming 50 Ohms of course. Watts, volts what ever... It looks like we are all in the same ball park. I'm anxious to see your data. These days the LNAs in the receiver front ends are often optimized for things other than impedance control (e.g., Noise Figure, whatever), and the impedance characteristics wind up being frequency dependent more than in the past. Doing link budgets in power units still works, but people tend to build test benches without power meters or spectrum analyzers, so often test equipment and test setups are still spec'ed with uV levels to keep the test stand simple. I prefer to keep everything in power units, but when the manufacturers give you the specs in uV, it just muddies the waters a bit. I suspect for avionics the uV specs may be from legacy methodologies to keep testing cheap and easy. Nobody wanted to buy power meters or spectrum analyzers in the 50s and 60s, and the test equipment will still be cheaper today if it can be avoided. Anyway, having different receivers side-by-side makes a/b testing reasonable, assuming the cables aren't crap on one side or the other. Quote Link to comment Share on other sites More sharing options...
Piloto Posted August 14, 2018 Report Share Posted August 14, 2018 The reality is that the electrical noise level is higher than the radio sensitivity. Too much sensitivity makes the receiver prone to intermodulation interference specially near broadcast FM/TV stations. José 3 Quote Link to comment Share on other sites More sharing options...
jhbehrens Posted August 16, 2018 Report Share Posted August 16, 2018 I've had an IFD540 that had very poor VOR reception when compared to a KX155 and I sent it back for a new one. Avidyne doesn't seem to test units very well before they send them out. So you should get a replacement. You installer should have checked VOR and ILS reception as part of the post-install checks if he had followed the install manual by the way.... Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted August 16, 2018 Author Report Share Posted August 16, 2018 6 minutes ago, jhbehrens said: I've had an IFD540 that had very poor VOR reception when compared to a KX155 and I sent it back for a new one. Avidyne doesn't seem to test units very well before they send them out. So you should get a replacement. You installer should have checked VOR and ILS reception as part of the post-install checks if he had followed the install manual by the way.... The VOR receiver performed better than spec. I was the installer. The problem was a bad connection in the cable between the radio and the nav splitter. Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 16, 2018 Report Share Posted August 16, 2018 Currently sitting in Moab waiting out the weather, but I did try several VOR sensitivity a/b tests getting here from Rapid City today. In all cases the IFD540 had much better sensitivity than my TKM, which has a better paper spec. I left my notes in the airplane, and I'll try to do some more tests tomorrow on the way home, but I was cruising at 10,500' and in a couple of instances the IFD either obtained or held lock on a VOR about 20 miles better than the TKM. The G5 doesn't show a flag, but it'll drop the deviation indicator bar when it loses lock, and I was comparing that loss of the indicator with the loss of the flag on the CDI connected to the TKM. I've no idea of the condition of the two cables from the splitter to the receivers, as those are being tested as well. That said, my IFD540 has to go back to the factory eventually because the BT and WiFi were confirmed by the avionics shop as fubar'd. So, yeah, maybe their production testing isn't what it might be. Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 17, 2018 Report Share Posted August 17, 2018 Quick update: today's trip verified what I saw yesterday, that in my airplane the IFD540 VOR has a LOT better sensitivity than the TKM MX-170C. I outbound tracked two different VORs until loss of signal on each unit and the IFD lost lock much later (about 20nm) than the TKM. This may just mean that my TKM setup is especially crappy, so take it for what it's worth. I wrote down the distances to the next waypoint in my route that each failed at, if anybody cares for actual data. 1 Quote Link to comment Share on other sites More sharing options...
Browncbr1 Posted August 21, 2018 Report Share Posted August 21, 2018 (edited) Did you check to verify your GS signal splitter or diplexer didn’t go bad? The ILS gs didn’t work on my gtn until I got a new one. PArt number was in the install manual. Needs a different one that kx155 uses Edited August 21, 2018 by Browncbr1 Quote Link to comment Share on other sites More sharing options...
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