MMDVM HS HAT not receiving weak signals
Posted: Sun Apr 25, 2021 8:33 pm
Hello,
According to Spec, the ADF 7021 can receive well in the -100dBm range. My pi-star is showing a different behavior: When my radio is close to the MMDVM, everything is fine. BER is well below 0.3%. The RSSI is indicated in the range of 45-50. When I increase the distance, in the range of about -70dBm the BER increases to 5% and more. If I increase the distance more, the signal is no longer detected.
To track that down, I created the following test setup:
[Radio] --- [Attenuator -40dB on Antenna plug] --- [Rubberducky] -------------------- [MMDVM HS DUAL HAT with the two supplied antennas.]
Results:
When the radio is within few centimeters around the antenna, I get around -50dBm signal. In ca 1m distance, I get around -70dBm, according to MMDVMHost log. Further away, MMDVMHost is not picking up a signal, so I can't tell RSSI in greater distance.
With Pi-Star, in close distance, everything is fine. In ca 1m distance, the BER rises and quickly the signal drops out when I increase the distance further.
I tried the same with MMDVMcal, and the weird result is, that in mode "b" the MMDVM HS DUAL HAT can receive the signal with BER below 0.5% from a distance of up to 3 meters and probably more.
I already tried using a simplex HAT - same behavior.
So my question: Why is MMDVMcal showing a low BER even on weak signals, while MMDVMHost can't receive below -70dBm and in more that 1m distance?
Remember - this is a heavily attenuated test setup to reproduce the problem without taking a walk In reality without attenuator on the radio, the problem starts in a distance of several hundered meters, even if connecting the MMDVM to my big Diamond station antenna.
Thanks in advance
DB9CR Christian
According to Spec, the ADF 7021 can receive well in the -100dBm range. My pi-star is showing a different behavior: When my radio is close to the MMDVM, everything is fine. BER is well below 0.3%. The RSSI is indicated in the range of 45-50. When I increase the distance, in the range of about -70dBm the BER increases to 5% and more. If I increase the distance more, the signal is no longer detected.
To track that down, I created the following test setup:
[Radio] --- [Attenuator -40dB on Antenna plug] --- [Rubberducky] -------------------- [MMDVM HS DUAL HAT with the two supplied antennas.]
Results:
When the radio is within few centimeters around the antenna, I get around -50dBm signal. In ca 1m distance, I get around -70dBm, according to MMDVMHost log. Further away, MMDVMHost is not picking up a signal, so I can't tell RSSI in greater distance.
With Pi-Star, in close distance, everything is fine. In ca 1m distance, the BER rises and quickly the signal drops out when I increase the distance further.
I tried the same with MMDVMcal, and the weird result is, that in mode "b" the MMDVM HS DUAL HAT can receive the signal with BER below 0.5% from a distance of up to 3 meters and probably more.
I already tried using a simplex HAT - same behavior.
So my question: Why is MMDVMcal showing a low BER even on weak signals, while MMDVMHost can't receive below -70dBm and in more that 1m distance?
Remember - this is a heavily attenuated test setup to reproduce the problem without taking a walk In reality without attenuator on the radio, the problem starts in a distance of several hundered meters, even if connecting the MMDVM to my big Diamond station antenna.
Thanks in advance
DB9CR Christian