The Model 34-PNB noise blanker is a solid-state noise blanker to be used in  TR-4C transceiver above Serial Number 31320.
	Unlike noise clippers or limiters commonly found in communication equipment, the 34-PNB is an advanced noise blanker which actually mutes the receiver for the duration of the noise pulse. Between noise pulses, full receiver gain is restored. (The receiver AGC is affected only by the desired signal strength, not by the noise at the antenna.)
	The 34-PNB is most effective on strong, periodic noise impulses such as ignition noise. The blanker is least effective on random noise. This noise is continuous in time and the information it masks cannot be recovered by either blanking or limiting techniques. However, loss of communications due to random noise is a rare occurrence, generally impulse noise is responsible for such situations.
	Low level signals masked by noise impulses without the noise blanker can be copied when the blanker is used. The 34-PNB is a must for the mobile operator because he can now blank ignition noise due to trucks and other cars as well as his own car.

	At the output of the receiver mixer, the signal follows two paths. The main signal path is through a delay circuit, an amplifier, the gate, then to the crystal filter into the I.F.
	The balanced gate is a noiseless electronic series switch that opens for noise impulses but closes to allow the signal to pass.
	The other path is through the noise processor. Here the noise pulses are converted to 2.15 MHz, and travel through an amplifier into the gate driver, which opens the gate at the instant each noise pulse enters it, on the way to the receiver I.F. The noise is stopped before the highly selective crystal
	filter causes the pulses to lengthen and mask more of the desired signal.
	Installation of the kit is about a two hour job for the competent technician only. It requires use of the usual hand tools, plus soldering iron and electric drill.

	Disconnect the power connector from the TR-4C or TR-4. Remove the top half of the transceiver cabinet. Remove the 7 pin jumper plug located in front of the power amplifier cage. With the printed circuit side of the 34-PNB facing the outside of the transceiver chassis, carefully plug in the 34-PNB.
	After it is correctly seated in the socket, install a number 4 self-tapping screw in each comer of the 34-PNB bracket to secure it to the transceiver chassis. Replace the cabinet top.

The BLANKER switch on the transceiver is used to turn the accessory 34-PNB Noise Blanker on and off. The Noise Blanker may be left on except when there is a strong signal within 5 kHz of the received signal. A strong signal which falls within the 10 kHz wide crystal filter in the Noise Blanker, and outside the 2.1 kHz wide crystal filter in the transceiver, will operate the Noise Blanker gate circuit causing distortion products. This limitation in the Noise Blanker is caused by the necessity of having a band-width in the blanker wide enough to minimize stretching of noise pulses before blanking. Under normal operating conditions, this limitation is no problem.

CIRCUIT DESCRIPTION.

This noise blanker system is composed of the three major networks described below. Refer to the block diagram and schematic diagram to follow this circuit description.

TRANSMITTING PATH.

The transmitting path consists of a single RC coupled 9 MHz amplifier which passes the transmitter signal through the blanker. The signal then passes through the crystal filter pass band and into the transmitter mixer.

RECEIVER PATH.

The signal first passes through a crystal filter with a bandwidth wide enough to pass most of the noise frequency components but narrow enough to keep strong adjacent signals from overloading the noise blanker amplifier. The signal simultaneously enters the noise processor and the delay circuit, a reactive network which compensates for the inherent phase-shift of the noise processing section. The 9 MHz receive amplifier provides an overall system gain for the receive path. The balanced gate is an electronic series switch that opens for noise pulses but closes to allow the signal to pass.

NOISE PROCESSOR.

The signal passes through the tuned 9 MHz amplifier and into the balanced mixer. This mixer converts the 9 MHz noise pulses to 2150 kHz and prevents the high level 6.85 MHz oscillator signal from reaching the amplifier strip. The 2150 kHz noise pulses pass through the two amplifiers, the detector and into the gate driver. The driver reverse-biases the gate at the instant a 9 MHz noise pulse enters on its way to the receiver IF. The gate then is controlled by the same pulse it is blanking, enabling it to respond automatically to pulses of varying width.