I’ve posted it above.
Mig21Bis Pilot’s manual clearly states the SPO10 picks up SRC and TRK, from an airborne H-J band radar, which commonly occur at MPRF/HPRF.
PRF can’t be higher than radar’s freq. (which is within SPO10’s op. bandwidth), so I’d really love to hear from those who “concluded” anything, how does the product of their “concluding” work.
Obviously, GJ copied figures from ED and it would be interesting to know where they come up with those figures for a PRF range.
The F-4J’s radar operates at a PRF of 300,000 Hz, which is well above the 8,000 Hz PRF the SPO-10 can apparently detect.
I don’t know where they got the performance figures from, but it was certainly not uncommon for early RWRs to be incapable of detecting pulse doppler emissions, so it seems entirely believable.
I doubt it since PRF of 300kHz wouldn’t give the radar more than 500m of range.
But still, do you have any source for that SPO10’s PRF “range”, other than what some dudes “concluded” on DCS forum?
Thanks for sharing this.
Well that confirms it then. The maximum PRF the SPO-10 can detect is 8,000 Hz, which means there is no way it can detect HPRF radars (which are by definition all over 30,000 Hz).
Here is the F-4J Weapons System manual:
The Pulse Repetition Interval (PRI) is 3.3 microseconds (0.0000033 seconds). The formula for PRF is:
PRF = 1/PRI
So:
PRF = 1/0.0000033
PRF = 303,030Hz
But this is just a velocity search.
You don’t get to fix the contact position, because the radar returns ambiguous range.
In 300kHz PRF, you get mere 500m of unambiguous range.
Everything farther is ambiguous range.
So, the most common ACM mode range is about 20km, which is about 8kHz PRF.
If you wanna scan further, you need to decrease PRF even further.
So you see, if you wanna launch you need to come down to SPO10’s PRF range, especially when it comes to SARH, because of fusing…at least with these radars.
Thx, now all makes sense.
Velocity search is the only pulse-doppler search mode the F-4J’s radar has.
The F-4J’s radar does not obtain target range during tracking by lowering the PRF, it would cease to be a HPRF radar if it did that. It achieves ranging by modulating the HPRF waveform:
And that modulation is only 85 Hz (SPO-10 won’t be detecting it - not that it would be able to even if it were higher):
Can you upload that manual?
So, what does the manual say about the max. range in that mode, at that PRF?
Thx, but I meant range for target distance reading.
Well that is the range info for track based on the PRF
Target is between 17.5nm to 26.5nm PRF 3 & 4 are used with a 85Hz modulation for ranging. The same 85Hz modulation appears to be used for any PD track. This allows for a velocity calculation and ranging. When in search there is no modulation and its only able to provide velocity and azimuth.
Either way, all of these PRF’s are well outside the SPO-10’s ability to detect.
Yeah, well, what I’m trying to determine the track accuracy, since apparently FM ranging isn’t actually ranging, but a range approximation.
Several U.S. fighters use a technique
called linear-FM ranging, where the PRF remains constant and
radio frequency is swept linearly upward. A crude range
estimate is then determined by comparison of the transmitted
and received RF.
Maximizing noise-limited detection performance in medium PFR radars by optimizing PFR visibility | IEEE Conference Publication | IEEE Xplore
Now, there’s a very interesting posting by the guy who claims to have been working on APG59s in F4J/S.
He mentions PD freq. of 40 usec, which corresponds to 6kHz PRF and a tracking range of 25km.
So, anything beyond 25km is of unambiguous range and the plane probably displayed VS tracks.
This is more appropriate for my Aim7 thread, but is connected.
Well, he got some of it right. Both short pulse and chirp were triggered by a 0.65 uSec pulse; however in Chirp mode, the 0.65 uSec pulse was run through the delay line (basically just a coil that was grounded at one end) resulting in the transmitter firing for about 65 uSec. The received pulse was run back through that same exact delay line for pulse compression. It wasn’t perfect; the compressed pulse was 0.8 uSec wide - but it was a heck of a lot stronger than the return from short pulse would’ve been. Best resolution was somewhere around 150-200 feet - but when you’re lobbing a missile at someone, that’s close enough
So, this is how the PD actually worked and the big reason for the abysmal Pk of the Aim7.
There’s more to read here, but I didn’t have time to, so we’ll see what’s going on in more detail.
Also, SPO10 can physically pick up any PRF from its op. band. That’s beyond the discussion.
The 1-8kHz filter is, probably, just set to avoid being triggered by an iPhone, or whatever, but filters can be removed and changed depending on the situation.
No it cannot, the manual for it states as much, I cannot find any reference for the filter being able to be turned off or adjusted, the system just isn’t that advanced. Just being “in band” isn’t enough, early RWR’s specifically had issues with detecting HPRF PD signals. Russian RWR during the SPO-10 to SPO-15 period was particularly poor.
There are early British RWR’s, that cannot detect a PD signal in band either.
Ok, I don’t think you understand the issue here…if a receiver can pickup J band (and SPO10 can) then it means it can pickup a wave of a frequency as high as 20GHz.
PRF is just the amount of those (20GHz) waves “fired” in bursts of certain lengths, which are BY DEFINITION, shorter than a carrier wave frequency.
So, there’s absolutely no physical limit for the receiver to receive this wavelength, only artificial and that’s most probably the filter.
F15s in Germany had velocity gate set to >150kmh because their Doppler wouldn’t screen BMWs and Porsches speeding on the autobahn. It doesn’t mean APG63 can’t track targets slower than 150kmh, but a matter of filtering.
Neither can early US systems, since they were a stop gap rushed into Vietnam to detect the SA-2’s and assorted Surface to Air threats, and even then there were still significant limits on them as well.
Though it is worth noting that this is a specific variant of the RWR which may well have been changed by the time the implemented configuration of the airframes in game as it only only specifically relevant to the F-4E(Blocks 31 though 42) and F-4J(Block 24 to 35, which may include those sent to the UK before they were modified, though I’m not sure what tail codes were sent) after consulting the Block chart for F-4s
Yes also long as that signal is in a PRF the RWR supports and won’t filter out. In the case of HPRF signals the SPO-10 is filtering out those higher PRF’s. Just as the video above demonstrates for US RWR. The manual for the SPO-10 has a PRF limit. So no it cannot warn you for those signals because it isn’t capable of doing so. If you want more simplified RWR mechanics than play Air RB where only the band coverage matters.
Can you share the source please?
