Dale Manquen posted:Bob, I would think that you would either use the 51K resistor to turn the current into a voltage that is read with DC volts, OR
Use only the capacitor and read the current directly with the meter set to microamps,
But not both resistor and current measurement.
Perhaps the meter's low resistance in the current measurement mode just swamps out the effect of the 51K resistor (which is in parallel with the meter), hogging almost all the current.
In the chip's data sheet there is a designation near the RSSI meter that is 100KV, which might have been an attempt to say that the RSSI meter movement should be a 100K ohm/Volt meter - more properly written 100K/V. A 100K/V meter that is 5V full scale would be a 50 uA movement.
None of this is critical for us if we just chose a circuit configuration and all use it. I suggest the 51K, .1 cap and the meter set to 2V DC. My gut feel is that we aren't going to get anything stronger than 2 volts for our whimpy pickup antenna.
(An improvement might be to use a ferrite-rod "loopstick" connected between the antenna input and ground to get a better signal, but this would also introduce a lot of directionality to the signal pickup, which might be different than the antenna plate of a diesel or the handrails of a steamer.)
FWIW, I used a 9V battery to power my R2LC. That way I just need to run a ground wire to the trucks - no rollers required. I just realized that I also used one of the 2411 PW metal flatcars, which might have a different characteristic than a plastic gondola. I did take care to rigidly mount the antenna, which is a chunk of brass rod.
Dale
I am sure there are several ways this can be implemented. I just followed what the specs indicated for the MC3372 IC, to get a RSSI output, using a 51K resistor & .1u cap. It gave us at the club what we needed, which was a way to measure signal strength as we tried different ways to improve the earth ground portion of the signal and get real time results.
Also, this all originally came from a post that Gary Emmich posted over a year ago on how to get signal reading off of the Lionel radio board, which I took the info and made up the signal car.
I can't find my original write up, so putting the pieces together again as we speak and I will sent out a post shortly with all the information I have on the signal car.
Bob D
