James Daldry W4JED
The voltage chart was written using the on-board "voltmeter".
Since it has a relatively low input impedance it will pull down
any voltage that has a high impedance source. Trust me - the
actual voltage on pin 3 of IC8, as with any op amp wired as a
voltage follower, is within a few microvolts of the voltage on pin
2. If you were to put a second voltmeter on IC8 pin 1 or 2 (they
are connected together) while checking pin 3 with the on-board
voltmeter you would find that all 3 pins would be at the same
voltage - within microvolts. The reason the on-board meter is used
is that that is the meter Hans knows that every QCX builder has on
These op amps used in these radios have a DC open-loop gain of 140 db. That's more than the path loss between the 50000 watt FM radio station you are listening to and your radio antenna. Any difference in DC voltage between pin 2 and pin 3 is magnified by 140 DB.
On 2/26/20 8:27 AM, John Brock wrote:
It seems to me the voltage measurement table in the instruction manual is off in a few instances. I am looking through the receiver function on my 20M QCX. It seems too quiet to me. Don't get enough volume. Hear a few faint signals. I will admit my Icom isn't hearing a lot on 20M either..