I find that the drive level needed for the Herc II varies from band
to band, but not that much ... 160 needs more drive than any other
band; 12 and 10 also need more, but not as much. This seems to be a
function of the tuning of the bandpass networks and the gain
characteristics of the final amplifier transistors. The gain is
actually set at TT to suit the set of final transistors in any
particular Herc. When they worked on mine they had to re-make this
adjustment. I get 450-500 watts out with the RF gain at 12 o'clock,
plus or minus an hour or so. Mostly I get full power just before 12.
On 17 and 15 I actually need to back the control off to around 10 AM.
This is into a matched feeder, or into a dummy load. If there is a
mismatch, then all bets are off.
If there is a bad joint anywhere outside the Herc and RF can leak
directly back into its input, then it will oscillate ! I suggest you
do the dummy load test and the also check to make sure the barefoot
rig is actually delivering rated output on all bands. If all seems
well then check those ground returns, coax plugs and leads for a bad
joint.
By the way, I added a massive ground buss to the cable from the 9420
PSU. Its made from 120 ampere highly flexible pvc jacketed
grounding cable, as used in industry over here. I soldered lugs onto
the stuff to make a set of jumper ground connections between the
OMNI-V, the Herc II and the 253 ATU. Note that before I got the fully
shielded 253, I had a breadboard ATU on the wall, well clear (I
thought) from the rig. It too was on the ground buss. But although
there was no obvious problem on CW, I had RF feedback, into the mike
circuit on SSB .... All RF interconnections were and still are in RG-8
cable, using military surplus C connectors (very large BNC in other
words) but that was not enough to stop 500w creeping back across the
room to the mike. (TT have an RFI fix for their desk mike - its awful
hard to cram the capacitors and ferrite beads into the TT mike plug
though. I gave up on it because installing the shielded 253 tuner
solved the problem).
Good hunting --- John G3JAG
On 07-Mar-99 Carter Grabarczyk wrote:
>
> Rick,
> Possibly an rfi problem. Leave the Herc out of the picture for a
> moment,
> reproduce the problem running barefoot and then switch to a dummy
> load
> and see if the problem goes away.
>
> 73/Carter/K8VT
>
> Rick Williams wrote:
>>
>> I was working the ARRL contest today and noticed something odd!
>> When
>> I went to 10 metres and operated barefoot the mic drive required
>> was
>> almost full clockwise (approx. 5 o'clock)! (I usually operate
>> with
>> the drive at about 9 o'clock position). This was the only place I
>> could get significant ALC indication and significant SSB output
>> (80 to
>> 90 watts).
>>
>> When I turned on the Hercules II and transmitted I needed to back
>> the
>> drive WAY back to about 10 o'clock.
>>
>> I tried the same operation on 12 metres and it behaved in the same
>> manner. Fifteen meters and lower frequencies are normal??
>>
>> What's happening??
>>
>
> --
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----------------------------------
E-Mail: patents@dx0man.prestel.co.uk
To: <tentec@contesting.com>
Date: 07-Mar-99
Time: 21:05:33
John Crux
Consultant in product forgery - Asia and
Africa
----------------------------------
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