[jdavis6809]

Marconi 2022 2955 replacement for OM345 OM360 Feedback please

Please let me know what other Marconi Instruments use these devices so I can check they are compatible to be replaced.

Does anybody know what the 1db compression point for the OM345 ? (not in the datasheet I have it is blank ).

Does anybody know what the 1db compression point for the OM360 ? (not in the datasheet I have it is blank).

Replacement for OM345

I have a Marconi 2022c which was faulty found three OM345’s faulty (bias voltages were miles out)

I did find a supply for the OM345’s from someone in South Africa wanting £25 each (not Philips modules) but decided to make my own. The AB1/2 board uses 7 OM345’s which would have been a total cost of £175 to replace all 7.
On the internet there was a design using a MAR6 but this has too much gain with bias current of 12mA having to replace resistors on the AB1/2 board. This is the wrong MMIC device to use for a drop in replacement.

I have made one prototype board with a MMIC and two 1.2k resistors in parallel to prove that the gain was 12dBm at a supply voltage of 12v. The bias voltage is 5v and the bias current is 12mA for a 12v Supply.
This led to building three prototype boards to put in the Marconi 2022c in IC positions IC8 ,9 and 10 on the AB1/2 board assembly .
Tests proved that the unit was working correctly also made no changes to the EAROM values.

I would like to explore the idea of making a PCB and supplying a built and tested modules please give me feedback so I can see that there is a demand to produce the OM345 replacement module. This would be a drop in replacement with no other modifications.
The overall height will be slightly higher due to the thickness of the plastic of the 0.1” header. This module will be far more reliable than the OM345’s

The contents are
1. PCB size approx 13mm x 8mm x 0.6mm double sided with ground plane
2. MMIC
3. 1.2k smd 0802 resistor x 2
4. 0.1” header x 5 round pin or flat pin no sure yet


Replacement for OM360

No tests carried out yet but I do have a MMIC in mind to get 24dBm gain. One problem faced with the replacement module is the bias voltage. In the Marconi 2022 the output load is open collector which feeds an inductor 2u2 (L26) to a 12v supply. Thus not a direct drop in replacement when using a 5v bias MMIC.
In the case of the Marconi 2022
There are 2 options
1. At the 12v supply end of the 2u2 inductor L26 insert a resistor in series with the inductor L26 so to give 5v bias.
2. Remove 12v supply end of the 2u2 inductorL26 and feed 5v from the nearest point on the board (in case of the Marconi 2022 there is another 2u2 inductor L33 nearby that is fed from 5v).

I would like to explore the idea of making a PCB and supplying a built and tested modules please give me feedback so I can see that there is a demand to produce the OM360 replacement module. The overall height will be slightly higher due to the thickness of the plastic of the 0.1” header. This module will be far more reliable than the OM360’s

The contents are
1. PCB size approx 26 mm x 8mm x 0.6mm double sided with ground plane
2. MMIC
3. 0.1” header x 10 (with 2 missing pins) round pin or flat pin no sure yet

Regards

John Davis
(RF design engineer by trade) Location UK