Posted by
Stephen W. Kercel on
Mar 17, 2009; 3:58am
URL: http://elecraft.85.s1.nabble.com/K3-Manual-change-suggestion-tp2479552p2489644.html
Don:
I'm glad to hear from you on this. I talked to Scott at Elecraft earlier
in the day, and he said that he had never heard of anyone using a tuning
pulser with a K2, but that if anyone would understand the possible
quirks it would be you.
In addition to the "one bar less than normal keying," I have discovered
another quirk. If I change bands, and then try to run the pulser, the
transmitter does not key. I hear the side tone, but the K2 power meter
shows no bars. Also, the peak reading Watt meter in series with my dummy
load shows no RF output. I can remedy the problem by reverting to the
regular keyer and tweaking the power level between QRP and QRO levels.
Somehow this seems to reset something in the rig. Once it transmits at
regular keying speeds, if I subsequently go to the tuning pulser, then
the K2 will transmit the pulses.
I have not yet looked at the RF output on a scope. What I have noticed
is that once the transmitter does turn on, the peak reading Watt meter
in series with the dummy load gives me about the same peak reading both
for the pulser and normal keying.
These various quirks do suggest to me that the the 12 ms "on" interval
is too short for the K2 to respond properly. Thus, your suggestion of
doubling the "on" interval sounds like a good possibility for
sidestepping these quirky behaviors. Both the "on" and "off" durations
are determined by a 0.1 uF capacitor in the timing circuit of the
pulser. If I change the capacitor to 0.18 uF (values of 0.2 uF seem hard
co come by), it would change the "on" interval to 22 ms and preserve the
33% duty cycle.
Unfortunately, the local Radio Shack does not carry these values, and
I'll need to order a new capacitor from Mouser. Thus, it will be a few
days before I can give this modification a try.
I'll let you know how it turns out.
BTW, for those who are curious, the Web page describing the pulser is
http://www.somis.org/D-a-09.GIFThe version that I built is the one transistor version.
TXN & 73,
Steve Kercel
AA4AK
Don Wilhelm wrote:
> Steve,
>
> I have not yet seen an answer on the reflector, so I will offer some
> comments. First, I do not think your pulser will hurt the K2 in any way.
> Secondly, I am at a loss to know why you do not see as many bars in
> the K2 LED display as you do in TUNE. The bargraph is relatively fast
> responding and should indicate the power level being transmitted. It
> may be that your pulser ON duration is too short and it causes a
> 'flicker' in the display that is not seen by the eye.
> It would be interesting to see what an oscilloscope connected across
> the K2 output would reveal (the oscilloscope display would react in
> even less time than the bargraph).
>
> So, bottom line, you may be seeing a natural result of the pulser ON
> time rather than an actual fault of the K2. Is there an easy way to
> double the ON time for your pulser? I find it hard to believe that 24
> ms of ON time would cause any problems for your amplifier - it
> certainly would not pose any problems for the K2.
>
> 73,
> Don W3FPR
>
>
> Stephen W. Kercel wrote:
>> Elecrafters:
>>
>> I built a tuning pulser to use with my K2/100 to tune an external
>> linear amplifier. The pulser is the AG6K design. The pulse is 12 ms
>> on and 24 ms off, and repeats about 28 times per second. This is (by
>> design) much faster than the normal 25 wpm or so keying out of the
>> keyer.
>>
>> The interface between the pulser and the K2 is a 2N2222 NPN
>> transistor used as a switch. The key line to the K2 is connected to
>> the collector of the transistor (nothing else is connected to the
>> collector), the switching data comes in through the base, and the
>> emitter is grounded both to the ground side of the pulser circuit and
>> the ground side of the keying line back to the K2.
>>
>> I notice what seems to me to be an odd phenomenon when I key the K2
>> with the pulser. When I first switch on the pulser, the power level
>> in the little LED power meter on the K2 shows the same power level as
>> I get in normal keying. However, after the first instant, the power
>> level indication drops one bar lower (and then stays there as long as
>> the pulser is on) than the power level indication under normal
>> keying. This effect occurs independent of the power level that I set.
>> It happens with the K2's 100 Watt amplifier both in and out.
>>
>> Is this simply an artifact of the metering circuit caused by the
>> peculiar duty cycle of the pulser?
>>
>> Most critically, will it harm the K2?
>>
>> Should I do as one alternative keying scheme shows, and use the
>> transistor to key a reed relay and use the reed relay (which would
>> simply hard short the K2 keying line on key down) to key the K2?
>>
>> TNX & 73,
>>
>> Steve Kercel
>> AA4AK
>>
>>
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