Jeff, the "earth ground" shown in the schematic is symbolic only for a
common connection. The circuit DOES NOT have to be connected to an
actual earth ground. In this case, the symbols represent a common
connection only. Saves drawing a few lines is all. Common practice in
schematics to avoid having too many confusing lines.
I would not worry at all about "earth" grounds, especially for r-f
purposes. A lot of myths about the subject. Unless you are being
troubled with "rf in the shack" don't sweat it. If you are, let me know
and we can talk about that.
You need to be sure that your station is connected to an adequate POWER
ground (60 hz) for safety purposes. If your shack is properly wired with
3-prong plugs and receptacles, you will be ok.
Thanks for posting this, by the way. Saves me a little futzing about to
find the right component values!
Jeff & Bea Hahn wrote:
>
> ICOm sent me the following project to make ICOM rigs operate at QRP
> levels. I would appreciate it if someone would tell me how to do an
> earth ground with the battery, R2 and the cable (my shack is on the
> second floor). I have tried to find the answer in books from the
> library but can find no discussion. One reference seemed to suggest
> that they should just be taped so there will not be a short and
> forgotten.
>
> *********
>
> QRP MOD FOR ICOM HF TRANSCEIVERS
> (from ICOM, dated 6/1/94)
>
> /
> |-------------/ *----/\/\/\/\----|
> (-) | S1 R1 | to
> *-----| | ALC
> < jack
> 9 volt alkaline battery R2 > <--O ---------O----->
> < | shielded |
> *-----| > | cable |
> | < | |
> | | | |
> | *----| |
> | | |
> ----|---- ----|---- ----|----
> ----- ----- -----
> --- --- ---
>
> With this circuit connected to the radio, the power output is
> adjustable between 0 to 100 watts. For best results, leave the RF
> power at maximum and adjust for desired power using R2.
>
> S1 is used to turn off circuit when radio is not in use or QRP
> operation is not desired.
>
> Radio Model: R1 Value R2 Value
>
> IC-761, 765 47K Ohms 20K Ohms
>
> IC-720(A), 735, 740, 2M Ohms 1M Ohms
> 745, 751(A), 275A/H
>
> IC-725, 726, 728, 729, 220K Ohms 100K Ohms
> 736, 737(A)
>
> *********
>
> Thanks,
>
> Jeff Hahn, KR4YS
-- 73, George Amateur Radio W5YR QRP-L #1373 AutoPOWER Systems Fairview, TX
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