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Azur Electronics

The HP 8418A Auxiliary Display Holder is also called Auxiliary Power Supply. Intended for use with the HP 8410C Network Analyser, but can also be used with the HP 8407A Network Analyser with Option H03, and the HP 8412B Phase - Magnitude Display, HP 8413A Phase - Gain Indicator or HP 8414A Polar Display Units. The original cost was $1,800 in 1980.

This 8418A is unusual as it has a remote-controlled 0 to 75dB Attenuator fitted, this is Option H01 and cost an extra $2,000 in 1980. The later 8418B had the attenuator fitted as standard.

Front view showing space for plug-in unit
Rear view showing connections

Rear Panel
POWER [CEE22 Plug]
TEST PHASE [BNC] from Network Analyser
TEST AMPL [BNC] from Network Analyser
REF [BNC] from Network Analyser
BLANK [BNC] from Network Analyser
ATTENUATOR CONTROL [14 way Amphenol Blue Socket] to Attenuator Control Unit

Amphenol Blue 24 way Connector for 8407A, 8410C, 8418A Mainframes and 8412B, 8414A, 8414A Plug-Ins, see Network Analyser Internal Connections for details. 

January 2008

Bought the 8418A (S/N 1708A) on eBay IT together with a 8414A.

February 2011

Downloaded Operating & Service Manual, A & B versions. The 8418A was completely stripped down to assembly level, cleaned up, labels removed and re-assembled.

The rear panel BLANK 4mm socket was damaged so this was replaced with a BNC socket.

The 8418A requires 4 signals from the Network Analyser: Reference; Test Amplitude; Test Phase; and Blanking.

Only the 8414A Polar Display does not require the Test Phase signal.
Rear connections
The A4 Attenuator Assembly 08418-60019 is fitted to the left hand side and is in circuit after the A3 Amplitude Vernier Assembly 08418-60004 (in the screened box). This provides the Test Amplitude output to the Display Units.

The A2 Phase Vernier Assembly 08418-60003 (in the screened box) provides the Reference output.

Both the Test Phase and Blank signals are fed direct to the Display Units.

Attenuator Assembly
The Attenuator Control socket provides +20V supply (via a current limiting resistor and protection diode) to one or more inputs (also diode protected) to select the attenuation required. This was intended for use with the 8409A Semi Automatic Network Analyser. Without any remote control connected, the attenuator is set to 0dB. With the remote control connected from 0dB to 75dB attenuation in 5dB steps is available.

 Pin No  Wire

Function  A4 XA4 
1 WH/OR 10dB Enable 6
4 GN 5dB Enable 7
7 WH/YL 40dB Enable 2
8 WH/RD 20dB Enable 4
11 BK 0V Ground 14
14 OR  +20V Remote Enable  9
I have made up a basic switch controller (Azur ACU109 Attenuator Control Unit) from scrap parts. It also has a LED at the back to indicate power is on. Not pretty but built for no cost! 
Azur ACU109 Attenuator Control Unit
Started on Performance Tests, power supplies ok but no display on the 8414A. Found that A2 & A3 pcb's had been swopped over inside the RF screened box. Luckily no lasting damage and after correcting this now have a display. Completed tests ok.

Tested Controller with another attenuator in the TEST AMPL circuit and magnitude dot on 8414A is controlled correctly.

Performance Testing
Network Analyser System
After modifying the 8407A, have now got this working with the 8418A to enable 2 Displays to be used at the same time. Tested with all combinations of the 3 Display Units and all ok. All 3 Display Units 8412B, 8413A & 8414A require the REF and TEST AMPL signals. The TEST PHASE signal is only required for the 8412B & 8413A. The -20V BLANK signal is not necessary as this has the same unblanking effect as no signal. This is supposed to blank the trace when phase-lock is not achieved, so maybe this is a fault with the 8407A or maybe is only a function of the 8410C.