Jujupilote wrote:
They could at least try to measure the amount of non txp traffic comparing primary and secondary radar data.
Not many UK ATSU have both PSR & SSR and when they do they are not necessarily in-sync for range, idents and min surveillance altitudes
Doing this experiment at large scale would require a herculean effort, it will amount to having a joined UK airspace from patched ATSU units nationwide: this is the cause why CAS busts are problem in the first place 
for start, what Farnborough sees as 200ft CAS bust on SSR altitude differs from what London Control sees due to dodgy altimetry practices, Thames SSR probably have no clue what Luton squawks are and no one want to scan it’s nearby Class G….
For sure a local UK ATSU don’t give a cent about primary returns outside lateral boundaries of their CTR, only those above it and also they don’t give a fuss about primary returns above, bellow, even inside CTA as they are deemed by default outside their CAS unless they send an altitude…
Maybe project for UK military (assuming budget) but they don’t have a clue about civvy SSR/Squawks and they filter out anything that flies bellow 250kts, remember even military pilots talking to Mil ATC in Northholt/Lakenheath do end up in Gasco when they nip Luton/Stansted airspace, only CAT airliners pilots seems to be off the hook on this campaign 
In the US, we now have the ADS-B mandate. As part of this, some of the secondary radars are supposed to be discontinued in low traffic areas. However, the FAA is keeping 100% of its primary radars. Primary radars can be used when ADS-B and secondary radar is not available. The controller sees a fused location of traffic being surveilled, including the ADS-B position, the transponder position of multiple radars, the primary target, and any multilateration systems input.
Someone did some slick software to merge primary with ADS-B.
the resolution would be 1-2° in azimuth, about the same in elevation
Do they have elevation? That would be extremely unusual. With a phase array radar (military) you get that easily but not with a normal rotating dish.
Peter wrote:
Do they have elevation? That would be extremely unusual
I am sure one that works to flag non-txp CAS vertical busts would require a lot of money, besides it’s “geometric-elevations” not “baro-altitudes”, in complex airspace with QNH, RPS, QFE, STD altimeters this matters a lot…
Of course with a federal budget you can get one of these in London Information room to monitor all traffic in/out/inside UK traffic rather than asking us that famous “1177, mooode Carlieeyyy, remain outside controlled airspace”
https://www.radartutorial.eu/19.kartei/03.atc/karte028.en.html
Peter wrote:
Do they have elevation? That would be extremely unusual. With a phase array radar (military) you get that easily but not with a normal rotating dish.
Do they actually used rotating dish?
I thought everything uses AESA these days. (https://en.wikipedia.org/wiki/Active_electronically_scanned_array)
Joined up radar services in the UK have been talked about for 15 years, if not more.
The services have not improved while airspace complexity and infringements continue to rise or remain constant.
They could at least try to measure the amount of non txp traffic comparing primary and secondary radar data.
I put this Q to a NATS/CAA (there is a revolving door between the two) guy last year and he said, basically, that the non-txp % is negligible.
Obviously to anyone who flies with TCAS, that doesn’t reflect reality at all (with the TAS605 since 2013, I would put the % at 50% below 3000ft, 75% below ~1500ft, and only a few % above 4000ft) but I can’t say with certainly that
Note also that the < 1500ft crowd will be invisible to much civilian primary radar so ATC won’t have useful data on non-txp % there anyway. And more thorough research on this would need collecting military radar data, which they do for an infringer who did a serious bust, turned off his txp and dived down, but it isn’t something one will be doing for a casual bit of research.
Schools tend to like INOP transponders, or INOP altitude encoders.
Ultranomad wrote:
Primary radars are fairly ubiquitous – those big radomes or big latticework antenna reflectors are all primary; secondary radar antennas look like narrow horizontal beams.
There are about 160 civil primary radars in Europe plus some military ones. Maximum range is typically 100-250 NM for enroute radars or 30-60 NM for approach surveillance radars, and the resolution would be 1-2° in azimuth, about the same in elevation, and 0.1-0.3 NM in range. The main problem in use is the lack of reliable identification of aircraft. It also costs a lot to operate, and a significant part of that cost is electric power. Power consumption grows very steeply with maximum range, as the required radiated power increases as the fourth power of range, whereas for a secondary radar it’s only the square of range.
Thank you.
In terms of identifying seperation from CAS it is relatively inaccurate?
To what extent is primary actually used? In other words is it running routinely, and who is actually using the information? I had assumed that we had largely fallen back on secondary and it is this the controller sees most of the time. Is it the case that controllers can typical switch to primary or do they regularly overlay primary over secondary?
Obviously for a rogue or genuinely hostile aircraft primary is going to be the sole means of identifying the bandit.
Primary is synthetically overlayed on the screen.
