That raises the issue of "duty cycle" from a ham's perspective. 100% duty
cycle is the Alpha advertisement - put a brick on the key and leaving it
there overnight. We always considered the SB amps good for their rated power
at 50% duty cycle. My interpretation of that:
- RTTY contest, in practice 50% xmt, 50% receive: no power derating required
- RTTY Ragchew, long xmt monologs: derate power output by 50 to 75%
-larry (K8UT)
A former Ham from Heath
-----Original Message-----
From: Joe Subich, W4TV
Sent: Monday, September 24, 2012 10:27 PM
To: rtty@contesting.com
Subject: Re: [RTTY] Heathkit SB-1000 On RTTY
REPLY:
Aren't Eimac's data sheets for 100% duty cycle?
The data sheet specifies "CW or PEP" and does not give any pulse
duration specifications. By definition PEP can't be 100% duty cycle.
One could do a lot of mathematical gymnastics comparing RTTY to SSB
or CW but CW transmit is what, 60% duty cycle ... even heavily clipped
SSB has around a 6 dB "crest factor" (peak to average ratio) while
RTTY is 100% duty while transmitting. Even with the same proportions
of transmit vs. receive time RTTY will generate as much as 4 times
the heat as either CW or SSB without even considering the effects of
cooling lag (ability to move the heat out).
73,
... Joe, W4TV
On 9/24/2012 4:34 PM, Bill, W6WRT wrote:
ORIGINAL MESSAGE:
On Mon, 24 Sep 2012 15:49:26 -0400, W4TV wrote:
600W output is close to the safe CW output! Eimac's data sheet gives
600W CW or PEP as the "useful power output" for a single 3-500Z with
2500V on the plate.
REPLY:
Aren't Eimac's data sheets for 100% duty cycle? I don't have an exact
value for
RTTY contesting but I would guess the worst case is a string of unanswered
CQs
at around 80%.
I agree however, it wouldn't hurt to drop it back to 400-500 watts RF out
or so.
At the receiving end they probably would not notice the difference.
73, Bill W6WRT
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