Racal RA6790/GM A1 Pre-Amplifier / Overvoltage Protection Module

  

For sale is a Brand New A1 Pre-Amplifier / Overvoltage Protection system for the Racal RA6790/GM receiver. It includes all necessary cables and connectors including mounting plate to install in any Racal RA6790/GM receiver. Full installation instruction are provided on CD.

The A1 Amplifier / OVP modules are comprised of receiver muting and RF input overload protection, followed by a RF pre-amplifier which may be included or by-passed by connection of liking plugs. The RF signal then passes on to the existing Low Pass filter module before entering the fist mixer stage of the receiver. The design of the overload and pre-amplifier circuits follow the original Racal A1 design methodology providing an additional 10 db of RF gain. It incorporates all of the Racal design upgrades and improvements that were implemented to the circuitry during its operational lifetime. The system comprises of two units, the OVP unit that attaches to the Antenna input connector J1 and the Pre-amplifier unit that is mounted into the accessories area of the receiver. The A1 module can be installed above any existing A5 ISB board and installation kits are available. The incoming RF signal passes from the antenna connector A1J1 into the OVP device containing a Lightning overvoltage protection GDT/ Arrestor circuit and then on to the main A1 unit. Entering Capacitor C1 and the fuse F1 providing additional front end receiver protection. R1 and R2 establish the bias conditions for diodes CR1, CR2 and CR3.

These diodes provide further input protection with CR2 additionally providing negative half wave rectification of the input signal. This negative voltage is limited to 0.6V below the 0V ground rail and is smoothed over C3 before being applied to Q1. R4 and R5 bias Q1 into conduction that energises reed relay RLA-1. This closes the relay and allows the incoming RF signal to pass into the receiver. If the incoming RF signal is greater than 6V rms, then the voltage provided by CR2 will turn off Q1 de-energizing relay RLA-1 and disconnect the high input RF signal level.

R6 discharges C3 quickly to allow for fast recovery from the RF overload conditions. External Muting is also possible by grounding the E2 input which intern switches off Q1 via CR4. CR4 protects Q1 from the external application of positive voltages. The RF signal is then passed through an optionally connected RF Pre-Amplifier and then out of the A1 module via E6 on to the existing Low pass filter unit. The RF Pre-Amplifier has a fixed gain of 12 db and consists of (Q2, 2N3866) and (Q3, 2N5160) in a complementary configuration.

The OVP module has an insertion loss of -2 db that combines to produce an overall gain of 10 db. The Pre-Amplifier is bypassed by removing linking plugs 3 & 4 and inserting a link into the plug 2 position. (The pre-amplifier is included in the circuit, when links 3 & 4 are in and link 2 is out). The A1 upgrade is "plug and play" and can be installed without any drilling or changes to the existing receiver.

The item "Racal RA6790/GM A1 Pre-Amplifier / Overvoltage Protection Module" is in sale since Saturday, October 17, 2020. This item is in the category "Mobile Phones & Communication\Radio Communication Equipment\Ham/Amateur Radio\Ham Radio Receivers". The seller is "philla6a2" and is located in Haverfordwest.

This item can be shipped to all countries in Europe, United States, Japan, Canada, Australia.

1. Model: Racal
2. Type: Pre-Amp / OVP
3. Brand: A6A2