2.假設有種雷達不受噪音干擾，那麼是否有方法可以讓他測到錯的距離？

How far the repeater jammer was able to move the false target away from the real one in the Fan Song s tracking was was the subject of intense research. Secret ELINT missions using C-97 transports flying in the Berlin air corridor recorded the Fan Song s antenna pattern, operating frequencies and power output. A radar (SADS-1) matching the intercepted characteristics was built and the jammer tested against it. Adjustments were made to the repeater jammer until it was able to move the false target a safe distance away from the real one.

System 13 and ALQ-51 was used effectively to protect the user aircraft on many occasions over China and North Vietnam. However, counter-counter measures were developed. First, the ChiCom introduced Lobe On Receive Only (LORO) on their Fan Songs in 1963. A dish antenna on top of the Lewis scanners sends a non-scanning beam to illuminate the target while the Lewis scanners scanned on receive only. The RWR only receives a non-scanning signal, the pilot may think that he is not being tracked and not switch the System 13 from stand-by to transmit. This was how the U-2 flown by Chang Li-yi was shot down over Paotow.

Worse still, missile fragments severed the wiring of the self-destruct charge for the System 13 on Chang s U-2. The system was compromised. The ChiCom realized System 13 was a deception repeater and the signals were entering through the Fan Song s side lobes. A Circuit 28 was developed that greatly reduced the effect of the deception jamming. This is almost certainly a side-lobe blanking system. The U-2 of Hwang Rong-pei was shot down in 1967 using a Fan Song equipped with this ECCM device. ChiCom accounts indicate that once it was switched on, the ECCM Circuit 28 blanked out the effect of the jammer. Later on, other more effective jammers were developed to defeat the improved Fan Songs. (ARMs also helped.)

Well, what do you think? Signal-to-Noise-Ratio (SNR) ... Automatic Gain Control (AGC) at the radar receiver ...

Here is what the text book says:

What is Range Gate Pulloff in radar?

Targets being tracked using range gates can attempt to employ a tactic known as range-gate pull off (RGPO) or range-gate stealing. The target uses a jammer to transmit the appropriate electromagnetic energy back to the tracking radar at the appropriate time and power level. Over the subsequent few pulses, the jammer progressively increases its transmitted power. This increased power is welcomed by the receiver circuitry and the receiver gain levels are progressively wound down to accommodate the increased received power. The receiver is, therefore, becoming increasingly de-sensitised to the real received energy. Once this process has continued for a short period of time, the receiver has become too insensitive to receive the real signal levels from the target alone. At this point, the target is said to have stolen or captured the range gates. Once the range gates have been stolen, the target can either switch the jamming off and force the radar to reacquire (taking valuable time for the AGc to adjust) or the jammer can commence transmitting false returns at ever increasing (or decreasing) time intervals to the tracking radar in an attempt to walk the tracker away from the target. Either way, the target has successfully performed deception jamming of the tracking radar.

Remember, even with high radiated power, a radar has to detect an echo reflected back from a distant target with signal propagation losses subject to the inverse square law. The jammer has less to do to produce a signal of sufficient gain to match that of an echo.

No, you cant, bro...:)

請問LORO系統是由PLA發展出來的嗎﹖

>A dish antenna on top of the Lewis scanners sends a non-scanning beam
to illuminate the target while the Lewis scanners scanned on receive only.
The RWR only receives a non-scanning signal, the pilot may think that he
is not being tracked and not switch the System 13 from stand-by to transmit.

小弟相關知識有限﹐有些疑惑
雖說碟形天線是送出non-scanning beam﹐但據您的說法是進行照明作用
那麼據小弟淺見認為照明是一種雷達波持續照射行為﹐RWR應該相當頻繁接收到這種
信號波﹐照理說應是更會警覺才是
還請指正小弟誤解之處

小弟有時沒空上網﹐先說聲謝謝

No, that was introduced by the Soviet Union. The first Soviet SAM system to use LORO for ECCM was the S-125 (NATO: SA-3 Goa). The RSN-125 fire control radar(NATO: LOW BLOW) had a single antenna that illuminated the target for two separate arrays to scan on receive. This system was developed in the late 1950s ChiCOM technicians sent to the Soviet Union for training on the V-75 (SA-2) would have been exposed to this technique. With the break down in Sino-Soviet relations, SA-3 and LOW BLOW was never transferred but the ChiCOMs developed their own LORO add-on for their FAN SONGs. The operational concept would have come from the Soviets but the ChiCOM developed their own version.

>那麼據小弟淺見認為照明是一種雷達波持續照射行為﹐RWR應該相當頻繁接收到這種
>信號波﹐照理說應是更會警覺才是

No, the illuminating radar uses pulsed signals to provide range data - it is not continuous wave (CW). The illuminaing beam would not be scanning and to the simple RWR of the period it would not appear to be locked-on and tracking.

Previously, the Lewis scanners of the FAN SONG would be sending beams sweeping left-and-right as well as up-and-down. When they lock on to their target, the sweeps would be concentrated around a narrower zone around the target and the pulse repetition factor (PRF) would increase to give more precise angular tracking and ranging. An RWR like System 12 would detect the increase in sweeps and the increased PRF and warn the pilot with a flashing light and a line trace on the display. The non-scanning signal from the illuminating dish would not appear to be an imminentthreat on the RWR and the pilot may not realize he is being tracked (on receive only) and would not take countermeasures in time.

PRF is not the only clue that an RWR gets when a radar is tracking. When tracking radars is trying to acquire a target, it scans over a wider area. For a conical scan radar like SON-9 the beam would be scanned in a wider spiral scan pattern. When they lock-on to a target, the scan patterns would be much narrower to generate more precise tracking in angle. The APR-25 RWR developed from System 12 gave audio indication of the scan rate so that the pilot can tell when the radar has locked on.

In the final engagement phase, the PRF of the fire control radar may be increased to give more precise tracking in range. System 12 had a 《High PRF warning light》 that gave warning when FAN SONG goes to the high PRF in preparation for launching missiles. Use a lower PRF radar to provide precision tracking before switching to the High PRF at the last minute to support missile launch and System 12 will not give enough warning time. That was how Terry Li (Nan-ping) was shot down.

For a Track While Scan radar like FAN SONG, the Lewis scanners would be sweeping its azimuth beam left-and-right and its elevation beam up-and-down over over a wide sector (20 degrees). The beams interect in a 10 degree by degree sector in the middle. If you find yourself in that sector (and the FAN SONG keeps you in that sector) then you know you are being tracked precisely and missile launch may be imminent.

The See-Sams receiver gives warning of when you are being centered in this Azimuth Sector and activates a warning light. This light is called the A.S. light and the pilots quickly nicked named it the《Aw Shit》light! When operating under LORO, ie. the ChiCOM version of the Soviet FAN SONG-E, the A.S. light would not give warning that you are 《centered》 and being tracked. That was how ... Chang Li-yi was ... etc.

SA-2 in command guided using a C-band uplink. When you receive THAT signal, you know missile(s) are on their way. The APR-26 was developed to detect the SA-2 command link signals. This was, again developed from a system first used by the CIA on U-2 (the WR-300). A warning light dubbed the O.S. - Oscar Sierra officially and 《Oh Shit》by the pilots - gave warning of the C-band guidance signal being transmitted.

Semi-active radar homing missiles use continuous wave (CW) illumination which has a completely different set of characteristics. If you are being tracked by a pulse radar eg. STRAIGHT FLUSH of the SA-6, and then a CW signal is detected, you know you are being illuminated for a missile launch.

> The APR-26 was developed to detect the SA-2 command link signals.

不客氣,覺得有點像寫武俠小說裡比武時「出招」、「解破」... 「中招」...

>>The APR-26 was developed to detect the SA-2 command link signals.

>Well, it rises another question. I know ROCAFs mirage 2000 having similar setup to detect the link between active radar AAM and the launching fighter. However, I did not learn such feature was equipped with any US fighter. Or I am wrong? mmm... most likely.
Thanks in advance.^^

ROCAF 戰機的電戰系統有甚麼功能不敢置評. Alfred Price 曾對「電戰」的報導有以下的評論:

「懂的不願說、願說的多半不懂」

我兩個都不是所以要承認 Whiskey Bravo Delta (WBD:「我不懂」! )

先進的電戰系統截收信號的能力很高，問題是截收到「信號」本身不等於得到有用的「資料」。要辨認出信號是甚麼作用就要依賴 ELINT 電子情報的「烏鴉」哥兒們。

某戰機的某型電戰系統能提供甚麼的警報多半是電子情報單位的功勞。俄羅斯先進戰機、雷達和飛彈的各種參數、資料等都已經洩漏給西方。某戰機的某型電戰系統能辨認出「羅宋」(Russian) 飛彈的中段導引指揮資料鏈的頻率應該不是意外的事。

這可能就是某廠商的「獨門暗器」。不過，誰有甚麼「暗器」、這些「傢伙」靈不靈就 ...