When will we get full TCS functionality?

[Southernbear]

3 hours ago, QuiGon said:

Well, I guess I have to try this myself, because I have the suspicion, that what @Southernbear described there might be an exploit, that allows you to get a radar lock on a target hidden in ground clutter with a 100% success rate.

My American's friend's Dad worked in the Navy on Submarines, had a F-14 RIO friend from the navy that told us about this. You keep the target locked at long as possible and if you do loose it through the notch and are close enough slap it into P-STT and while you'll get ground clutter the TCS allows the dish to ignore a lot of it allowing for much more reliable AIM-7 shots.

 

Haven't tried this with the AIM-54 but frankly at the ranges I'm talking about I'd only use one if I didn't have an AIM-7

It works because P-STT or the CW search mode doesn't have doppler notch gates...if you dive to the deck its still going to trash the lock, but at 20-40k feet if someone tries to do a lateral notch and go cold on you by switching it to P-STT but keeping the TCS locked to the target it prevents the radar loosing the target nearly as much as it might without the TCS's help

[QuiGon]

8 hours ago, Southernbear said:

It works because P-STT or the CW search mode doesn't have doppler notch gates

And that's why I don't understand why you turn off the clutter filter. If you have slaved the radar to the TCS and guide a Sparrow towards the TCS target by just blasting CW radar energy to where the TCS is pointing, then I don't understand what difference it makes if you have the clutter filter on or off.  Doesn't the clutter filter only apply to PD modes anyways?

[IVAN01rch]

2 hours ago, QuiGon said:

And that's why I don't understand why you turn off the clutter filter. If you have slaved the radar to the TCS and guide a Sparrow towards the TCS target by just blasting CW radar energy to where the TCS is pointing, then I don't understand what difference it makes if you have the clutter filter on or off.  Doesn't the clutter filter only apply to PD modes anyways?

Well, it can be night night or clouds or haze preventing TCS from working. PD works much farther compared to P or TCS. If the background to the target is clear sky than you will get much more reliable lock without the filter. 

[QuiGon]

1 hour ago, IVAN01rch said:

Well, it can be night night or clouds or haze preventing TCS from working. PD works much farther compared to P or TCS. If the background to the target is clear sky than you will get much more reliable lock without the filter. 

Why radar lock if the radar is slaved to the TCS and is just pointing the CW antenna to where the TCS is looking?

[iantron]

Why radar lock if the radar is slaved to the TCS and is just pointing the CW antenna to where the TCS is looking?

A pulse lock provides range for missile guidance. CW though shouldn't be able to range the target though. I think we're talking about the TCS keeping the radar pointed in the right direction until the RIO can obtain a supplementary pd-stt or p-stt lock to supply range.

Regarding the MLC conversation, turning off MLC would allow ground clutter and the real return in. If there was sufficient "contrast" maybe you could still get lock. I don't know. Alternately if you already have a PD-STT or a P-STT then the returns are filtered by the range gate, effectively eliminating the ground clutter unless the target is "very" close to the ground.

Anyone know how long the range gates are?

[iantron]

Also I think this is what the PD clutter knob is for. There may be situations where auto control is filtering too aggressively and you can just turn it down instead of off.

[DSplayer]

3 hours ago, iantron said:

Also I think this is what the PD clutter knob is for. There may be situations where auto control is filtering too aggressively and you can just turn it down instead of off.

Of course this doesn’t apply to DCS though.

[cheezit]

3 hours ago, iantron said:

Also I think this is what the PD clutter knob is for. There may be situations where auto control is filtering too aggressively and you can just turn it down instead of off.

 

Is this knob supposed to affect the width of the main-lobe clutter filter, or something else?  Doesn't seem sensible for it to affect the width of the zero-doppler-shift filter (ground clutter has a doppler shift roughly equal to that of the ground, not zero), and I don't have a good enough understanding of the system to think of anything else it might be doing.

 

The AWG-9 had a fully analog front-end and a programmable digital computer back-end, the latter consisting originally of the CDC 5400B with a 24-bit word size and 1 MHz clock speed, 24k NDRO memory, 8k DRO memory, and 140k replaceable tactical tapes that acted as ROM.  Were the doppler notches implemented in the analog front-end (eg. with band-reject/notch filters implemented with op-amps and passive components in the signal chain) or the digital back-end?  A turnable knob could easily adjust either - eg. a trimpot could adjust the resistance of one part of a voltage divider in a filter circuit, or a rotary encoder could adjust filter parameters in a digital system.

 

It's funny, by the way, just how many digital computers were in the "all analog" F-14A.  You've got the MP944 in the CADC that everyone knows about, the CDC 5400B in the AWG-9 that I just mentioned doing target tracking and generating steering commands and keeping track of launch parameters and driving the TID and DDD, also the smaller CP-1050 in the AWG-9 that I think was used for stores management and a few other things.  Were there more?

[Naquaii]

45 minutes ago, cheezit said:

 

Is this knob supposed to affect the width of the main-lobe clutter filter, or something else?  Doesn't seem sensible for it to affect the width of the zero-doppler-shift filter (ground clutter has a doppler shift roughly equal to that of the ground, not zero), and I don't have a good enough understanding of the system to think of anything else it might be doing.

 

The AWG-9 had a fully analog front-end and a programmable digital computer back-end, the latter consisting originally of the CDC 5400B with a 24-bit word size and 1 MHz clock speed, 24k NDRO memory, 8k DRO memory, and 140k replaceable tactical tapes that acted as ROM.  Were the doppler notches implemented in the analog front-end (eg. with band-reject/notch filters implemented with op-amps and passive components in the signal chain) or the digital back-end?  A turnable knob could easily adjust either - eg. a trimpot could adjust the resistance of one part of a voltage divider in a filter circuit, or a rotary encoder could adjust filter parameters in a digital system.

 

It's funny, by the way, just how many digital computers were in the "all analog" F-14A.  You've got the MP944 in the CADC that everyone knows about, the CDC 5400B in the AWG-9 that I just mentioned doing target tracking and generating steering commands and keeping track of launch parameters and driving the TID and DDD, also the smaller CP-1050 in the AWG-9 that I think was used for stores management and a few other things.  Were there more?

No, the PD CLUTTER and PD CLEAR knobs were settings for gain for the clutter and clear regions, i.e. the hot and cold sides of the MLC. The doppler filters in the AWG-9 were not controllable in this way.

[iantron]

I'm not sure what you mean by the clutter and clear region if not the actual MLC region. Is there an amplifier governing the area just outside of the MLC filter? Or are you saying that the returns within the MLC have an adjustable gain?

[Southernbear]

On 2/9/2022 at 7:45 PM, QuiGon said:

And that's why I don't understand why you turn off the clutter filter. If you have slaved the radar to the TCS and guide a Sparrow towards the TCS target by just blasting CW radar energy to where the TCS is pointing, then I don't understand what difference it makes if you have the clutter filter on or off.  Doesn't the clutter filter only apply to PD modes anyways?

The AWG-9 has a +/- 200Knot doppler notch filter when in PD search, it means when the target notches you and their relative velocity drops within that band, the lock is lost. By going to P-STT and turning this off, you can't notch the radar just by going abeam to it. Normally due to the ground return even at 20-30k feet it you can still loose the lock when the relative velocity nears 0...however if you have the target locked with the TCS you don't have to worry about the lock slipping onto a ground return or getting confused by some other artefact and it can guide the AIM-7 through the notch.

Keep in mind you can do it without the TCS by just going into CW, but locking them up with the TCS helps keep the target locked up AND if you happen to loose lock you hit the STT button again and since the TCS is already making the dish point at the target it instantly relocks the target. 

[QuiGon]

20 minutes ago, Southernbear said:

The AWG-9 has a +/- 200Knot doppler notch filter when in PD search, it means when the target notches you and their relative velocity drops within that band, the lock is lost. By going to P-STT and turning this off, you can't notch the radar just by going abeam to it. Normally due to the ground return even at 20-30k feet it you can still loose the lock when the relative velocity nears 0...however if you have the target locked with the TCS you don't have to worry about the lock slipping onto a ground return or getting confused by some other artefact and it can guide the AIM-7 through the notch.

Keep in mind you can do it without the TCS by just going into CW, but locking them up with the TCS helps keep the target locked up AND if you happen to loose lock you hit the STT button again and since the TCS is already making the dish point at the target it instantly relocks the target. 

Thanks, that makes it a bit clearer. Especially the last sentence is an important bit of information that I was missing, because it says, that you have to manually hit the STT button to regain a lost lock. That wasn't clear to me before and I was under the impression, that the radar would somehow obtain a STT lock automatically if slaved to the TCS.

What I still don't understand is this:

20 minutes ago, Southernbear said:

The AWG-9 has a +/- 200Knot doppler notch filter when in PD search, it means when the target notches you and their relative velocity drops within that band, the lock is lost. By going to P-STT and turning this off, you can't notch the radar just by going abeam to it.

Why do you have to turn the doppler notch filter off, when you're using pulse modes?

Edited February 10, 2022 by QuiGon

[cheezit]

1 hour ago, Southernbear said:

The AWG-9 has a +/- 200Knot doppler notch filter when in PD search,

The main-lobe-clutter filter is +/- 133 kts (relative to Vg) and the zero-doppler filter is +/- 100 kts (relative to 0 Vc)  in all PD modes, no?

[cheezit]

16 hours ago, Naquaii said:

No, the PD CLUTTER and PD CLEAR knobs were settings for gain for the clutter and clear regions, i.e. the hot and cold sides of the MLC. 

I'm sure it'll never happen, but I really want to see the schematic for the circuit that implements this, as the normal/straightforward way one would implement a band-reject filter would preclude this.  I'm mostly a firmware guy, but I can think of a couple of more complicated ways to structure things to allow this functionality, and I'm curious whether the guys at Hughes took the same approach.  Especially considering that the AWG-9 was under development before packaged transistor-based op-amps became easily available, so the whole thing might be some clever MacGyveresque combination of a couple of BJTs and resistors.

Man, I'd love to have a poster of that schematic for the wall of my 'office'.

[Naquaii]

15 hours ago, iantron said:

I'm not sure what you mean by the clutter and clear region if not the actual MLC region. Is there an amplifier governing the area just outside of the MLC filter? Or are you saying that the returns within the MLC have an adjustable gain?

It's not an amplifier and it's not in the MLC. I mistakenly said gain when I really meant thresholds and those can be set independently for the regions above (clutter) and below (clear) the MLC.

1 hour ago, cheezit said:

I'm sure it'll never happen, but I really want to see the schematic for the circuit that implements this, as the normal/straightforward way one would implement a band-reject filter would preclude this.  I'm mostly a firmware guy, but I can think of a couple of more complicated ways to structure things to allow this functionality, and I'm curious whether the guys at Hughes took the same approach.  Especially considering that the AWG-9 was under development before packaged transistor-based op-amps became easily available, so the whole thing might be some clever MacGyveresque combination of a couple of BJTs and resistors.

Man, I'd love to have a poster of that schematic for the wall of my 'office'.

As above I said gain when I really meant thresholds. The doppler filter banks used to determine what rate a return has have two threshold settings, one for the region above MLC on the DDD (Clutter) and one for the region below MLC (Clear). All you see on the DDD is really synthetic returns representing the doppler filter banks having a detected return, that's why the PD returns are small squares unlike pulse. So the threshold knobs are really the level at which the filter is regarded as having a return detected.

This isn't really possible to model in DCS in any realistic fashion as this depends on a lot of factors not present. IRL they were recommended to be left in the detent where the computer controlled them.

[cheezit]

28 minutes ago, Naquaii said:

This isn't really possible to model in DCS in any realistic fashion as this depends on a lot of factors not present. IRL they were recommended to be left in the detent where the computer controlled them.

Send Nicholas Cage to steal a copy of Tactical Tape 116D while I work on a CDC-5400B emulator based on this outdated spec from before the subassembly was even named .  We'll get this done 

[Badger1-1]

Will jester be able to use these tricks and and switch off the filters? Or at least will we be able to tell him?

[LorenLuke]

What's the status on this capability?