GTR200B not breaking squelch

RV74ME · #1 05-24-2021, 02:05 PM

Noticed lately missing radio calls from ATC because they weren’t breaking squelch. If I turned squelch OFF (press power knob), I could hear their calls loud and clear. Turn it back on, and nothing. Doesn’t happen all the time, but enough to where I can’t trust it. And it’s usually an ARTCC frequency. Today in was ATL and JAX center at 10,500’.

For those not familiar with this radio, there is an RF squelch setting in configuration mode. Settings are 0-10. The default is 0, and is most sensitive (should let even the weakest transmissions thru) and where mine is set. In normal mode, the only squelch control is either ON or OFF. No in between.

Anyone else having similar issues or have suggestions on what to try?

Thanks

Longez · #2 05-24-2021, 03:42 PM

Steve,

One quick check is to make sure that pin 5, TX Interlock In is not grounded.

TX Interlock In is an active low input that desenses (protects) the COM receiver when a 2nd COM radio in the same aircraft is transmitting.

Having this input permanently grounded would significantly impact your receiver range.

Steve

RV74ME · #3 05-24-2021, 04:05 PM

Thanks Steve, i will check. Looking at my wiring diagram, I don’t have a wire going to pin 5. I’m single radio, so that makes sense. But I will pull the radio to verify

deene · #4 05-24-2021, 06:48 PM

RF squelch is set in the configuration mode which is very easy to use. Get a GTR200 install manual for details.

If you don’t have access to the manual, contact me via email and I’ll send a copy.

Deeneogden(at)Gmail(dot)com

RV74ME · #5 05-25-2021, 06:14 AM

Quote:

Originally Posted by deene

RF squelch is set in the configuration mode which is very easy to use. Get a GTR200 install manual for details.

If you don’t have access to the manual, contact me via email and I’ll send a copy.

Deeneogden(at)Gmail(dot)com

I have the manual, and RF sq is set to zero

RV74ME · #6 05-25-2021, 10:22 AM

Just took to avionics shop to do a vswr check. Reading was about 1.6 (good/normal) throughout normal freq range, so that tells me we can eliminate the coax and antenna. Stumped

bjdecker · #7 05-25-2021, 11:01 AM

Systems and Dynamics Questions:
What type of antenna (mfg, make, model) are you using? Where is it installed? Type of cable/terminations?
On which frequency are you missing calls? Have you tracked it down to a particular sector/transmitter/RCO location?
Propeller Type? RPM when issue occurs? Flight attitude - climb, descent, etc.?
Aircraft Lighting? Other RF sources active?

I ran into similar issues with my GTR200; at a certain distance and altitude from the tower, with a certain prop RPM I could not receive and my transmissions were not received. Changing aircraft attitude, RPM, altitude, combination of all three would resolve the issue.

I rationalized/explained it to myself as some kind of blanking effect by the propeller disc and the line of sight + signal polarization (antenna is a bent whip) issue .

RV74ME · #8 05-25-2021, 11:55 AM

Quote:

Originally Posted by bjdecker

Systems and Dynamics Questions:
What type of antenna (mfg, make, model) are you using? Where is it installed? Type of cable/terminations?
On which frequency are you missing calls? Have you tracked it down to a particular sector/transmitter/RCO location?
Propeller Type? RPM when issue occurs? Flight attitude - climb, descent, etc.?
Aircraft Lighting? Other RF sources active?

I ran into similar issues with my GTR200; at a certain distance and altitude from the tower, with a certain prop RPM I could not receive and my transmissions were not received. Changing aircraft attitude, RPM, altitude, combination of all three would resolve the issue.

I rationalized/explained it to myself as some kind of blanking effect by the propeller disc and the line of sight + signal polarization (antenna is a bent whip) issue .

Delta Pop comm antenna, mounted bottom of fuselage underneath pilot seat. BNC connecters. All looks good.

It's weird. There's no rhyme or reason. Yesterday it happened while at 10,500' talking to ATL center, then again with JAX center. Only reason I knew they were calling me was a relay from another aircraft. As soon as I turned the squelch "OFF", by pushing the power button, I could hear them 5x5. Loud and clear. And I've never had a transmit issue. I'm always told my transmissions are loud and clear.

I should also mention that Garmin just sent me another brand new GTR200B to try, and it happens with this one too. That tells me it's not the radio, unless it's software issue (squelch sensitivity). But not sure, because I haven't heard yet of anyone else with similar issue.

bjdecker · #9 05-25-2021, 11:59 AM

PM sent .........

baumrick · #10 06-05-2021, 09:19 AM

Same issue withy recently installed GTR200. I have a bent whip antenna mounted on the bell aft of the baggage compartment. Check connections and everything appears in order. I'll need to get in and have a more detailed inspection soon. I would greatly appreciate any info if someone comes to a conclusion on what the issue is.