OpenGD77

I have several FM (analogue) receivers and comparing it to radioditty they have much less background noise. If we look at the s-meter, they are very quiet while the GD77 signals S5, s7, both at home and in the middle of the country. It is most evident in VHF. The signals received from repeater stations, however, are very similar between all devices. This means that I have less dynamic bandwidth with radioddity and weak signals are heard with a lot of noise, compared to other walkies.

I have three GD77s, and with them all, the same.

I don't have a look if it happens with the stock firmware, but I'm scared that this noise will affect the weak DRM signals as well.

How do you look at the S meter on the official firmware ?

Did you connect a dummy load and observe the RSSI level on 2m and on 70cm ?

VK3KYY wrote: ↑

Thu Feb 27, 2020 11:15 am

How do you look at the S meter on the official firmware ?

Did you connect a dummy load and observe the RSSI level on 2m and on 70cm ?

I can't watch the S-meter with the stock firm, but I can hear the repeaters. Let's see if this weekend I can test and compare 2 gd77 in fm, one with the opengd77 and the other with the factory firmware.
And I will also look at the signals on a dummy load.

I'll tell you the result

The GD77 hardware does suffer from overloading of the front end by strong signals on nearby frequencies. This can make weak signal detection difficult. This is especially true on VHF. It is mostly noticed when using an external antenna but can also be seen sometimes on the stock antenna.

I am not sure if this applies to your tests. The basic GD77 when tested without strong signals is normally very good.

G4EML wrote: ↑

Thu Feb 27, 2020 1:16 pm

The GD77 hardware does suffer from overloading of the front end by strong signals on nearby frequencies. This can make weak signal detection difficult. This is especially true on VHF. It is mostly noticed when using an external antenna but can also be seen sometimes on the stock antenna.

I am not sure if this applies to your tests. The basic GD77 when tested without strong signals is normally very good.

could we say that the 5 FM commercial transmitters with 500w each that are about 3km in a straight line could saturate the receiver?

That would be an explanation. I understand that I may need some sort of filter at the input.
Something similar happens to the Icom 7300 on the 20-meter band, when the propagation is good and the broadcasting stations close are very strong. There I can attenuate the effects by inserting an antenna tuner into the RX line

That’s quite possible. The front end amplifiers are broadband so they are very prone to overload. The most likely culprit would be powerful FM broadcast stations.