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SL-30 monitor mode

Scott Will

Scott Will

Well Known Member
My SL-30 works grreeeeaaaatttt when I don't use the monitor frequency function. When I monitor a frequency, the freq being monitored pulses. Any way to fix that?

It didn't do this in the past. I know pulsing can be related to engine monitor but I have absolutely no pulsing when listening on the main com. Only when I put the monitor on does the 2nd freq pulse. The first stays clear.

Just in case I made sure the NAV side wasn't monitoring as well. RG-400 throughout.

Any ideas?
 
SL30 monitor function

Scott--I think that is by design. Mine "pulses," and always has. I've flown other aircraft with Apollo radios and they behave the same way.

My understanding of the way the monitor functions is that it rapidly switches back and forth between the two frequencies, unless there is a transmission on the "active" freq, which temporarily deactivates the standby monitor function.

Since there is only one radio, I don't think it can really simultaneously monitor two active frequencies. If it didn't toggle back and forth even while there was a transmission on the standby freq, you'd potentially miss transmissions on the active freq.
 
I always run my SL-30 in monitor mode, and I have no pulsing whatsoever. I have to look at the radio to see the little 'M' in the window to be sure I'm monitoring when the radio goes 'quiet'. For what it's worth, I fly with Lightspeed 20XL headsets. I'm sorry I can't offer anything to help fix your problem but no pulsing here at 2500+ hours. Rosie
 
SL30 Monitor Freq Pulsing

This thread got my attention as I'm planning am SL-30 for my RV-10. I'm also a 25 year amateur radio op, so have some questions, comments.

The only way to have true dual receive is with two receivers. Everything I've read about the SL-30 indicates a single receiver with a monitor function, that checks the monitored freq at some rate/interval. Need check manual or with Garmin to see if this rate is adjustable, or if pulsing is normal under certain circumstances described. Also, is this pulsing problem happening on all freqs, only certain combos, or?

I also wonder if this pulsing is prop or engine RPM dependent. This could be tested in flight easy enough. Ditto for airplane's orientation to station. There could be a multipath interference situation being created between the comm antenna and propeller. There could be a frequency in the engine, likely ignition system, that is beating with the SL-30 receiver oscillator so as to create a rhythmic, intermittent signal strong enough to open the squelch on the monitor or primary side.

Speaking of squelch, there could be an Automatic Gain Control (AGC) setting that is out of whack. We call this AGC pumping in ham radio, sometimes user adjustable in amateur radio equip, but almost always needs a pro with schematics, service procs, test equip, where aircraft avionics concerned.

Just some thoughts. I'll be following this thread, as this problem could be very annoying with an SL-30 in my RV-10.
 
Forgot to mention that the pulsing occurs whether the engine is off or on. Antenna is away from electronic ignition however there are some engine monitor wires in the vicinity (they cross perpendicularly). But as I mentioned above, I have no pulsing whatsoever when not monitoring.

Using Lightspeed 30-3G's.

Merry Christmas!!
 
SL-30 pulsing

Any way to power down everything but the SL-30 and see what happens? Airplane orientation to station should still be considered. If problem then goes away at power down, power back up one electrical device at a time. I would also talk to an avionics tech experienced with Garmin SL-30 before I went to too much more trouble. And, even if powering everything back up individually reveals a likely interference source, something could still be wrong, internally, in SL-30, i.e. poor ground, AGC, re interference/RFI rejection.
 
SL-30 / GX-60

Turn your stobes off then try it.

There is NO pulsing on my GX-60 and SL-30. I have at least one if not both monitoring another channel. SL-30 always has 'guard' tuned in.

I do not see this problem listed in the troubleshooting section of my SL40 Field Service Manual.

The only time I have NOISE on my SL-30 is when I press the ID button to listen to the NAV and forget that I selected another function.
 
Scott,

It's on purpose, you can't change it, and it's described in the manual. I found it a bit weird at first, but it's supposed to alert you that you're listening to a monitored frequency and head off a response transmission by you on the active frequency.

John Siebold
 
RV6_flyer said:
There is NO pulsing on my GX-60 and SL-30. I have at least one if not both monitoring another channel. SL-30 always has 'guard' tuned in.
Click to expand...

This is interesting. We have one GX65 equipped airplane that definitely does this, as well as my RV-8 and a friend's -8A with a GX60. It's subtle and I've never found it particularly troublesome.

Are we talking about the same thing?

All traffic on the active freq is always clear, with no pulsing at all. The only thing noticeable at all is about a 4hz "pulse" over transmissions on the monitored frequency. It is most noticeable on long transmissions with some background noise, like ATIS tapes. As far as I can tell, it's always at the same rate and intensity, and is independent of any other electronics in the airplane. It's exactly the same in all three airplanes I've experienced it in.

I think it's subtle enough that you might not notice it if you were'nt compulsive or were'nt going out of your way to look for it.
 
GX-60 No pulsing monitor mode

No pulsing, ever, in 400hrs with my GX-60 in monitor mode. Of course, as of yesterday, my GX-60 won't even turn on, crapped out inflight yesterday. :eek:
 
RV6_flyer said:
There is NO pulsing on my GX-60 and SL-30. I have at least one if not both monitoring another channel. SL-30 always has 'guard' tuned in.
Click to expand...
Pulsing is an exaggeration, but you CAN hear the sample rate. My GX-60 and SL-30 both do it. Then again I can hear the difference between 192kbps MP3s and CDs and some people can't.
 
Listening to ATIS or ATL center is where it gets really bad for me, personally. The audio drops out for about a 1/2 sec every 1 - 1.5 sec or so. I wonder if there's an internal setting because some people notice it and others say it's OK. Guess I'll just have to hop in another plane with similar radios to find out.

But if I was designing a radio like this, I'd probably do it just as they implemented. You have to check the other freq some way.
 
Scott Will said:
Listening to ATIS or ATL center is where it gets really bad for me, personally. The audio drops out for about a 1/2 sec every 1 - 1.5 sec or so. I wonder if there's an internal setting because some people notice it and others say it's OK.
Click to expand...
That's definitely not right. Either the active COM freq is breaking squelch momentarily, or there's something wrong with the radio or the setup.

FWIW, the "pulsing" I hear doesn't cause the signal to drop out. It's a rhythm more than a pulse... :rolleyes:
 
I have really bad hearing in certain freq ranges. If my GX-60 has been doing it, I've never noticed it. I guess I shouldn't say it has NEVER pulsed, but I can say I've never NOTICED it pulsing. FWIW.
 
Scott Will said:
Listening to ATIS or ATL center is where it gets really bad for me, personally. The audio drops out for about a 1/2 sec every 1 - 1.5 sec or so.
Click to expand...

Dan's right--that's definitely not right. What I hear is a split-second dropout 3-4 times a second. It's sort of like listening to somebody in a poorly tracked helicopter (think comedy traffic report). For short transmissions, it's not noticeable, and of course when there's no traffic on the standby freq, it's not evident at all.
 
tobinbasford said:
No pulsing, ever, in 400hrs with my GX-60 in monitor mode.(snip)my GX-60 won't even turn on(snip)
Click to expand...


Tobin--it's evident that 400 hours of pulses built up inside your radio and blew out your flux capacitor.

You need to replace your blue smoke :D
 
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James,

Where'd you get that smoke-in-a-jar. I've looked all over for that stuff. I think Advanced Auto parts used to carry it. I had a jar of that stuff once, but when I took the lid off to charge my wires back up all the smoke escaped into the atomsphere!! :D

BTW, it was the GPS fuse that blew on my GX-60, Comm fuse is still intact, but unfortunately I lost the whole screen so even if the radio is working I have no idea what freq it's on.
 
dan said:
Pulsing is an exaggeration, but you CAN hear the sample rate. My GX-60 and SL-30 both do it. Then again I can hear the difference between 192kbps MP3s and CDs and some people can't.
Click to expand...
Reading this thread I have come to the conclusion that I like a few others are not able to hear well. I cannot tell the difference between MP3 and CDs. The manual says click but I cannot and have not heard it. Must be AGE. They say that the mind is the 2nd thing to go and I cannot remember what the 1st is. Am starting to wonder if it is hearing.
 
Got back from flying today (first time landing in North Carolina!). My original estimation of the length and frequency of the "pulsing" was not accurate. It's much faster and not as long as I originally guessed. It's more of a moderate/fast ticking like sensation.

My radio system is fine, IMHO. I guess it's a phenomenon that I'll have to live with. My wife always says I have "super hearing" (and she should know since she has the MD degree to prove it, I guess). I'm gonna check out a few other airplanes and compare.
 
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