The place for technical discussions about GA and flying.
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By tsdesign
FLYER Club Member  FLYER Club Member
#1720711
I changed our GNS430 to 833 a while ago. Everything seemed fine, then recently trying to talk to Duxford (122.080) I found I could transmit to them but couldn't receive. Since then I've had to switch to box2.
I thought this was a problem with Duxford as every other station I spoke to was fine, then the same thing happened with Lydd.
Reverting to the old Duxford frequency 122.075 works fine on tx and rx. I understand (there's some very good threads on this forum) that the transmit frequency doesn't change between 25 and 833, but the receiver bandwidth is reduced on receive. So it seems my GNS430 has a problem with centre frequency on receive in some cases.
For now I'm reverting to the old frequency.
Has anyone else has this problem?
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By T67M
FLYER Club Member  FLYER Club Member
#1720883
It could be that Duxford's Tx frequency is slightly off, but as I believe ground stations are checked annually, and to a tighter tolerance than the equivalent check done on aircraft as part of the "radio annual", it might be worth getting your (presumably fairly old) GNS430 checked for accurate centre frequency in 8.33kHz mode.
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By Trent772
#1721233
Similar issues in our RV7.

Check aerial cable - needs to be RG400.

Do you have a USB outlet in your aeroplane - they spew out RF.

Try those and see, sorted us out.
By Peter Kelly
#1721254
This is a not an unusual problem when changing GNSx30 units to 8.33 mode.

The GNSx30 have different settings for RX squelch in 25KHz and 8.33KHz receive modes.

Check the RX squelch setting. It's in the set up menu - hold down the function key as you power-up.

That solves 90% of issues.

Otherwise, as per the previous poster, it won't help if you have some nasty spurious broad spectrum emiter (e.g. a poor quality USB power source). This will necesitate having the squelch set to high.

Poor quality coax cable, connectors and antenna more likley to degrade transmit function but worth checking. Should ideally be a single length of RG400 from box to antenna with no in-line joins.
By tsdesign
FLYER Club Member  FLYER Club Member
#1723249
It was the 833 squelch setting, thanks very much Peter Kelly, for saving me IRO of £800 - the cost of sending the 430 back to Garmin for checking. All working fine again now.