Radarbox - RF specifications?

[Fenris]

Does Airnav provide any specifications for the Radarbox in terms of noise figure, RF sensitivity, SNR for a reference BER on the recovered data? I have looked about, but can't find anything of this nature.

I'd like it to do some system calculations with respect to antenna gain, height, cable loss, benefit of preamplifier etc.

Thanks!

[Fenris]

I note that the SBS-1 data sheet indicates a sensitivity of -90dBm at its RF input connector.

Is Airnav able to comment on whether the Radarbox sensitivity is of a similar level?

[tarbat]

-105dBm.  Posted on a previous thread - http://www.airnavsystems.com/forum/index.php?topic=256.msg1881#msg1881

[Fenris]

Ah, thanks for that. I hadn't found that thread despite a search.

I'm wondering what is the effective bandwidth of the Radarbox receiver now. The sensitivity figure should be thermal noise level + bandwidth correction + receiver noise figure + required demodulator SNR. It's interesting to note that the -105dBm figure is 15dB lower than the SBS-1 data sheet quotes, that in itself should translate into a range improvement of a factor of 5.6 which seems much too large.

[Allocator]

I think that with so many possible influences - location, antenna, obstructions, aircraft attitude relative to the antenna etc - judging performance by the specification alone is going to be somewhat pointless.  After all, it is the manufacturer that publishes the figures in the first place.  Also, is this a minimum figure or an average to be expected if 100 boxes were to be tested?  If you read the "other" forum, then you will see that users really wanted the new version to be better than the last one, but other than a general feeling that it was better, nothing was really proved.

When I compare the performance of my RadarBox, I see a noticeable difference during high and low pressure periods.  Of course, even this might be a coincidence as the low pressure days might just have been low traffic intensity days and everybody may have been flying when the pressure was high - who knows :-)

[Fenris]

I quite accept that there are a lot of influences, and one that is not well understood is the effect of multipath and signal collisions on what is a very old and unprotected modulation scheme. It's very different receiving a line of sight signal to receiving a signal that is suffering from multipath and hence has inter-symbol interference.

What I'm getting at is that I'd like to know that a Radarbox sent a test signal at a known signal level from a quality signal generator will correctly decode at the relevant error rate.

I found another paper which quotes a required SNR of 11dB for a Mode S receiver. With a receiver bandwidth of just over 4MHz, that equates to 77dB (66 + 11) above thermal noise, which gives -97dBm. Now since a receiver can't have a 0dB noise figure that will actually degrade a little more, so let's say -95dBm is the best possible sensitivity. So we have 10dB to find to get to the figure from the thread that Tarbat mentioned, and that's a lot!

Specs can be notoriously difficult to create and to comprehend, I don't doubt that a Radarbox works in reality, I just like the numbers to add up correctly, after all I'm an RF Systems engineer!

[Allocator]

Brian,

Can't you carry out these tests yourself, as you sound like you know your wiggly amps :-)

[Fenris]

Brian,

Can't you carry out these tests yourself, as you sound like you know your wiggly amps :-)

I'll have to see if I can create the correct modulation format. I have access to signal generators which will transmit arbitrary waveform data, but actually creating that data is more difficult, the software I use is more angled towards creating OFDM for WiFi signals.

[flightchecker]

Does Airnav provide any specifications for the Radarbox in terms of noise figure, RF sensitivity, SNR for a reference BER on the recovered data? I have looked about, but can't find anything of this nature.

Good question Brian,
"sensitivity figures" a big nonsense of course (exept for sales arguments) without a REFERENCE to be coupled with.
By checking commercial transponder specs. you may find a 90% reply rate to be the reference mentioned. Sensitivity -74dbm only !!! (BW 3MHz@3db b.t.w.)
That's what one would call an "honest statement".
Technical literature regarding "secondary radar" typically specs -90dbm for a ground station receiver and -77dbm for its airborn counterpart. Reference the above "90 % reply" again. (BW 6MHz@3db this time)
Strange enough, whether one nor the other party is making use of the reference as described before or any other one. So, as long as there is none: forget about sensitivity !


Karl

[viking9]

Hey guys. This is getting to be like the photography sites where tyros argue about diffraction, pixels per micromillimeter, MTF and other technical stuff. In my 30 odd years as a licensed radio ham I never measured anything but SWR. I got my antennas as high as possible with the lowest loss cable I could afford and worked over 180 countries on HF. I think the same applies to Radarbox.

BTW, on the photography sites the people who discuss the technicalities ad infinitum don't seem to publish any photographs. Not that I'm drawing any parallels in this case.

[Fenris]

I've spent all my professional life (and yes, I've also held an amateur radio licence for a month short of 30 years) needing to measure the RF systems I design and build, otherwise no one else will believe that they perform as I say they do.

One of the things I'm interested in is being able to use the specifications of the Radarbox, the antenna gains, cable losses, and known line-of sight path losses to be able to predict and confirm the actual performance that I see from the installed system. Much as I would (and do to the best extent I can) with any HF or non-HF amateur system that I use. And yes, it's a lot harder with HF propagation because the path losses are much more difficult to quantify.

I'm not trying to catch anyone out here, but surely Primetec's manufacturer has a production test spec that is applied to the Radarboxes coming off the line to ensure that they have been correctly built and that they meet the specified performance? Otherwise you're handing over a lot of cash on a promise that is not that easy to confirm.

If you've seen the gyrations at the Kinetic forums where the 3dB sensitivity improvement of the SBS-1e is being questioned because some people can see it and others cannot, then you can see why I'm puzzled by what appears to be a 10dB discrepancy.

[flightchecker]

Seems it's not "tyros" discussing here as you might have noticed Tom, and as long as they don't harm anyone else, why not let them do so? That's what a forum is supposed to be for, isn't it?, and if one does not want to participate in a posting like the above, he's not urged, not even to read it.
On the other hand, there might be "techies" that are most likely interested if it comes to technical details about this our hobby, (I'm a confessing one) as well as "non techies" that might be willing to learn "one or the other".
 
My opinion, that I'm probably not alone with,

Karl

[Cumulus]

My opinion, that I'm probably not alone with,

Karl

You are definately not alone on this Karl, probably one of the most interesting threads I have read on this forum.

Regards,

Peter

[viking9]

Karl,

I was just making a comment. I would not want to stifle technical discussion but I feel that it might make non-technical people feel that they had to have technical knowledge to get the best out of their RadarBox.
 
I'm actually a retired techie myself - avionics, airframes/engines and IT networks. As the RadarBox, like a camera, is essentially a passive piece of equipment (OK so somebody is going to tell me it radiates) then surely there is really no need to know anything other the operating frequency and the impedance.

Tom

[Fenris]

Tom

Please don't think I was complaining at you either, I wasn't. We all have different views of the level of interest to be found with a slightly technical hobby!

If you think about the system, one thing that I'm trying to get a handle on is the effect of a preamp on sensitivity. In theory, since something like the ELAD preamp claims a 0.9dB noise figure and 12dB gain, it should be possible with knowledge of the Radarbox sensitivity and noise figure and the cable loss to work out what the system performance is, and thus determine for a given installation how much sensitivity can be clawed back with the preamp. In other words, is it worth stumping up 155 quid extra?

There's some method in my madness you know :)