Charged the 7AH gel cell at somewhere around 250mA for about 6 hours and bingo, I can keep 11.8 volts? at a measured (cheap SWR meter measurement!) "5 W" output.??
With a CW signal at 3.510? MHz (LSB) I then worked sequentially through a series of additional attenuator pads to try and calibrate the ICOM 718 S Meter
FIRST -- I check for "bleed through" by searching with no connection at all to the ICOM718 reciever --- while I could hear the signal (not strong, but there) -- there was ZERO indication onthe SWR meter.? ?So I think there is little bleed through in my MEASUREMENT apparatus.
All measurements have approximately 50 dB contributed by the resistive divider I built into the BNC pickoff on theHeathkit Cantenna
PAD ATTENTUATOR? ? ? ? ? ? ? ?S Meter Reading
20 db? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? S9 + 25 dB
20 + 6 dB? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? S9 +? 20 dB
20 + 6 + 20 dB? ? ? ? ? ? ? ? ? ? ? ? S9? ? ? ? ? ? ?-- so the 20 and 25 db points on the scale above S9 seem reasonably relatively accurate
20 + 6 + 20 + 6? ? ? ? ? ? ? ? ? ? ? ?S 8 & 1/2
20 + 6 + 20 + 6 + 6? ? ? ? ? ? ? ? ?S 8? ? ? ? ? ? -- so the S unit between S8 and S9 is worth about 12 dB
20 + 6 + 20 + 6 + 6 + 6? ? ? ? ? ?S 7 & 1/2? ?-- continues the trend that an S unit is worth about 12 dB on this particular radio at? that frequency
=? 20 + (44 db)
Note that the last line is 20 +? 44 db -- roughly right at the FCC requirement if the fundamental is at S9+25 --- so if the fundamental is at S9+25, the goal is to get all spurious responses below S 7.5 on this meter.? ?
Within homebrew accuracy anyway.....
I think this is correct thinking....
Gordon Gibby
Gordon Gibby
