[RTTY] Heathkit SB-1000 On RTTY

[Larry Gauthier (K8UT)]

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 at 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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