morinmau

On 07/11/2020 at 18:07, Geminids said:

Hi Morinmau,  a pretty basic question but are you sure of the frequency of that signal and that it is GRAVES?  I do not know the Noolec NESDR SMArTee v2 dongle but the ubiquitous FCDP+ can be a few hundred Hz off frequency - having said that, I have just looked at your last spectrumlab plot and the meteor ping is around 900 Hz with the "GRAVES" signal is just below.

Hi Mike, the Noolec was already frequency calibrated, so the signal is indeed GRAVES. Below you'll find two examples of genuine captures along with a spell of GRAVES beacon.

Cheers

Maurizio

20 hours ago, Geminids said:

Your reasoning for elevation angle is sound, but if you are still getting the main beam signal directly as it seems you are, then I would suggest that you are seeing the main beam through one of the antenna side lobes.  Try higher angles of elevation, changing antenna polarisation or pointing away from GRAVES.  From your location I would think you get very strong pings from meteors wherever you point.

By the way where did you get the map that you have drawn your directions on?

Mike

Hello Mike,

i'll try all alternatives bearings and see what happens.
I'm sure I dowloaded the map from some forum o blog, i just added the two coloured lines. I can attach the original one, but i don't remember the source.
Cheers

On 06/11/2020 at 01:21, wxsatuser said:

The double traces and diverging ones are more than likely aircraft returns.

Hello wxsatuser,

Ok but why i don't get the 'usual' streaks at low speed/doppler shift that means a reflection from a plane (as I see in waterfalls from other radio stations) ?

Hello guys,

I recently set up a meteor echoes detection station using GRAVES radar as transmitter. I have a problem with the signal from GRAVES, i'd like to know your opinion.

I live in Northern Italy, about 80km south of Milan (44.988211N, 9.124843E). Initial antenna (yagi 5 elements) bearing was toward GRAVES radar, so azimuth 314° and about 25° elevation (in order to cross GRAVES beam at 100km height), horizontal polarisation. Distance from GRAVES is 384km. I use HDSDR going to SpectrumLab through virtual cable. Receiver is Noolec NESDR SMArTee v2 dongle.

GRAVES beacon is always present, I would say 70-80% of the time on 24h basis, from strong to medium weak. Furthermore, the signal drifts in frequency from its main location, and often doubles. Some waterfall examples below.

As you can imagine, when the signal is strong enough, i can get as much as 50% false positives on the total hourly captures. I implemented several test in SpecLab CA to filter the beacon out, but essentially without success. I even set up two frequency bands for trigger (each with different thresholds), but since the signal is drifting sometimes, the 'rejection' band spell should be too large to be effective, so to remove GRAVES beacon but I also miss genuine captures.

So, I moved antenna orientation toward west, azimuth about 270° and lower elevation, around 10°. In the map below you see original antenna setting (in green) and this 'west' position (yellow line). I thought that is the most extreme position you can pick up in order to be still in GRAVES radiation area.

The situation slightly improved (GRAVES a bit weaker in average) but nothing changed in term of false positives.

My impression is that I'm too 'close' to the radar, but honestly i don't understand (technically) how the signal (that comes from tropo reflection) could be sometimes so strong and persistent, since I don't see the TX directly, and tropospheric conditions are far from ideal this period.

Any suggestion is welcomed.
Maurizio IU2JWG

Hello Steve & Blue Stragger, first i wanted to start a new topic, but it would have been a clone of this one: I have exactly the same issue you Steve experienced.
I live in Northern Italy, about 80km south of Milan (44.988211N, 9.124843E). Initial antenna (yagi 5 elements) bearing was toward GRAVES radar, so azimuth 314° and about 25° elevation (in order to cross GRAVES beam at 100km height), horizontal polarisation. Distance from GRAVES is 384km.

GRAVES beacon is always present, I would say 70-80% of the time on 24h basis, from strong to medium weak. Furthermore, the signal drifts in frequency from its main location, and often doubles. My waterfall is very similar to your Steve. Some examples below.

As you can imagine, when the signal is strong enough, i can get as much as 50% false positives on the total hourly captures. I implemented several test in SpecLab CA to filter the beacon out, but essentially without success. I even set up two frequency bands for trigger (each with different thresholds), but since the signal is drifting, the 'rejection' band spell should be too large to be effective, so removing GRAVES but also (most of) genuine captures.

I move antenna orientation toward west, azimuth about 270° and lower elevation, around 10°. In the map below you see original antenna setting (in green) and this 'west' position (yellow line). I thought that is the most extreme position you can pick up in order to be still in GRAVES radiation area.

The situation slightly improved (GRAVES a bit weaker in average) but nothing changed in term of false positives.

Now .. Steve, did you solve the problem ? In case, what did you do to achieve that ?
My impression is that we are 'too close' to the radar, but honestly i don't understand (technically) how the signal (that comes from tropo reflection) could be so strong and persistent, since I don't see the TX directly, and tropospheric conditions are far from ideal this period.

Any suggestion is welcomed.
Maurizio IU2JWG