HF Multicoupler Build
With only two antennas and many receivers I needed to have some type of Multicoupler I could connect all the radios to so I didn't have to keep reaching behind radios and connecting/disconnecting antennas. I've had a copy of Phil Atchley's LF-HF Receiver Multicoupler for some time and decided it was time to build this Multicoupler.
|First thing needed was to determine what to build this into. I had an old Jerrold Modline-12 TV Filter laying around that I was probably never going to use and decided to build it into this chasses.||
Here's the schematic of Phil's circuit he designed. I did some performance checks during and after this project and this design is an excellent Multicoupler design, well done Phil. I will present that data later.
I have since learned that Steve AA7U and Phil collaborated together on the Multicoupler design. Steve did the original Paint diagram for Phil and also originally bread boarded the circuit and tested it on the bench for Phil, making some changes to arrive at the final circuit. great job by both of these guys.
I decided to make 8 outputs and make the BCB filter in/out switch able. I also decided to modularize the construction so BCB filter would be a circuit board, input driver would be a separate ckt brd, each of the 8 outputs would be a separate ckt brd, and the power supply would be a separate ckt brd.
|I worked on the BCB Filter first. Before etching a board I wanted to check the performance of the BCB Filter so I bread boarded the filter and swept it. Above are the results, very impressive, great job again to Phil and this design. I have marked the frequencies for the markers shown in the trace.||Thought you might be interested in the test setup I used for sweeping. I used an HP8601A Sweep Gen, HP8600A Marker Gen, Heath 337 Demod Probe, Heath IO-4550 O'Scope and an attenuator I made because I needed to control the level of the sweep sawtooth to the Horz input to the scope. Above are the pieces.|
Here's the basic test test setup. The Demod probe is a negative detector so it produces a negative output voltage proportional to signal level. In the waveform shown above you can see that the positive part of the waveform is actually the BCB attenuation, this is why the above waveform shows a positive going attenuation trace.
|Here's a couple shots of the completed BCB Filter board.|
|Driver Brd was next.||
Next was the output boards. Yes, I made 8 of them. Above shown in various states of assembly. Heat sinks are definitely required and Phil specifies this in his design. The Outputs are emitter follower circuits that are biased so that half Vcc is on the emitter and you will have about 120ma of static current flow through the output transistor. So, with about 6.5 volts across the transistor and 120ma flowing through it P=EI says that statically the transistor will need to dissipate about 780mw. They do get warm so I would not chance doing without the heat sinks.
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