The AM Forum

Well, after a bit of work, here is the completed and working AM detector audio monitor.

It features Steve/QIX's low distortion detector circuit.  I added four selections of RF resistive attenuation (pick-up) to sample directly off the 50 ohm coax inner conductor. It accepts any power level from 10 watts to 1500 watts.  It has a buffer and phase reversal after the detector.  I also built in a 7 watt audio amplifier to drive the headphones.

It will accept audio input from either the HPSDR or FT-1000D and PTT switches it so I hear either receive audio or my monitored transmit audio in the headphones.

Notice all boards and parts are readily removed and accessible for easy servicing. Lots of room in there. The two signal diodes are on stand-offs for easy replacement.

So far it sounds very FB.  It is painted white and black lettered in the same shack style as the other HB gear.

Built from recycled scrap yard aluminum at $1/ pound.

T

The Disco Duck:


To follow the circuit and technical details, goto:
http://amfone.net/Amforum/index.php?topic=33280.msg257639;topicseen#msg257639

Kewl Beans man!..
Got a closer shot here..

Very nice Tom.
I no keep up wid u.  Too many prorects. Too many.  How you do?

Disco Duck!   ;D ;D ;D

HA!  Jeff you are officially promoted to official JJ shack art director.  For Your first project please make up new color logos for each rig. (Fabio, Rico Suave, Dr. Love, Disco Duck, Mr. Clean, etc)    ;)


Rick, it's now on to the next project!  I just tore down all the control wiring in the shack. What a mess. After 20 years there were too many add-ons and I was forgetting what the hell was going on when something broke.  So starting from scratch.

I've come up with a unique idea (at least for me)  where I will build a universal control box. Instead of a custom control and power supply for each situation, I will now have jacks for 5V, 12V, 24V, -12V available.  In addition, there will be MANY sets of N.O. contacts, NC contacts, 24V keyed, 12V keyed, etc.   In total, there will be 27 different phono jacks that can be routed to any rig for any purpose.  Easy to change around. Before, I had to get out the soldering iron and custom make stuff up whenever a new rig was added or changed around.  No more.  I've found we never know what a rig will need for keying, voltage or control. They're all different, thus needing a universal approach to prevent rat nests.

I should have it working in a day or so and will post some pics.

T

It looks great. What is the connector for the RF input? BNC?

Yo Op,

Glad you like it.

I'm using just a simple RCA phono jack and plug for the RF input. (with coax)  The main sampling resistor at the 50 ohm pick-off is a 5 watt 2K and isolates it. When in the 1500 watt mode, there is an addtional 50K resistor in series. So there is hardly any voltage or current involved at the input to the AM detector unit.


T

The Universal Station Controller is a good thing to have.  I made the one I am still using today, back in 1975 or thereabouts.

It has 2 output types:

Output 1) When going from Receive to Transmit mode - immediate action, When going to Transmit to Receive mode - delayed action  24VDC and 120VAC outputs.  These voltages are immediately active when put into transmit mode, but are subject to an approximately 1/4 second delay when going to receive.  The T/R relays, receivers mutes, VFOs and RF DRIVERS are hooked to this circuit.

Output 2) When going from Receive to Transmit mode - delayed action, When going from Transmit to Receive mode - immediate action.  These 24V and 120VAC outputs are delayed for a small bit of time (about 100ms) to give everything that was connected to Transmit Immediate (above) time to settle and become active.  Things like HV power supplies, transmitter output enables, etc are hooked to these circuits.  When going to receive, these outputs are immediately turned off.

All of the audio in the station also routes through a central audio patch panel, so anything can be patched to anything.

Without this type of setup, at least for me, the station would be unmanageable.  I have no fewer than 4 transmitters set up at any one time, along with NUMEROUS experimental transmitters, receivers, modulation monitors, recording devices, input sources (microphones, etc). etc, etc. etc. etc.  It would be a nightmare to have to try to handle all of the possible interconnects without the audio patch panel.

Another feature are separate mixers for everything BEFORE the audio processing, and another for everything AFTER the processing.  This is important for being able to play back recordings without going through the audio chain, which would obviously alter the original audio in some way.

It did take time to set up, but the whole thing, along with the audio processing fits in a 3 foot table rack.  When I have had to move this equipment around - for whatever reason there might be, the whole rack stays as one unit, so nothing has to be disconnected or otherwise dismantled.

Also, there is a central playback/receiver audio system for the station with 5 inputs for various receivers and other patchable sources, separate level, bass and treble controls - one set of each for the loudspeakers and headphones, and switches to turn either or both (speaker and headphones) off or on at any time.  There is a relay to switch between the mod monitor output on transmit, and the selected receiver output on receive - of course, there is a switch to override this if you wants to listen to one of the receivers instead of the mod monitor when transmitting  ;)

You will definitely NOT regret building such a system for your station!!

Regards,

Steve

Fantastic work Thom!  I have been using Steve's REA modulation monitor with his low distortion audio detector for years!  So what you hear is what you got!  

I will likely do something similar to what you have crafted for some of the other stations around here.  

Steve, since the REA mod monitor is no longer available it may be worth doing a small board set up for just the RF detector and audio monitor.  You could offer it just like you do with your other boards and let folks build their own and package it the way they see fit.    

Monitoring one's signal properly is a must.  

Joe, GMS    

Hi Joe, a new version of the Modulation Monitor is forthcoming!  It will have a good audio monitor (with AGC built in!) and some other features too  8)

Great Steve!  I know you were working on a software version, but with me I still do not allow computers in the Ham Shack  ;)! 

Joe, GMS