[Elecraft] JT65A output power variations.

[Matt Zilmer]

Since you're using USB, you might want to be sure you have the TX EQ
"flat".  Or use DATA A, where the EQ doesn't apply.

73,
matt W6NIA

On Wed, 11 Nov 2009 11:28:36 +0100, you wrote:

>Hi Julian,
>
>Thank you for your fast answer!
>A 1st point, as with the FT857, i'm using
>USB mode for JT65A. For the filter used,
>i ordered a 8 poles 2.8k with my K3,
>but i'm not sure if the 5 poles 2.7k "original"
>and always installed as FIL2 is not
>selected during TX???; next week-end, when
>active at my "external" shack, i will look how
>to remove the 2.7k filter, as i've also problem
>with center filter when i adjust the HI LO
>filter controls; when the 2.7k filter is (automatically)
>selected, i've a big discontinuity  with filter setting.
>
>As you say, i will look if the 2.7k is not selected
>during TX. I read also the "problems" when in
>DATA A mode, but as said, i'm working in USB
>(as recommended for JT65A for all RF bands)
>and VOX work at perfection too.
>
>My best 73, Rudolf
>HB9ARI
>
>PS As i expect to get 50W output when i set
>the control to 50W, i've adjusted the audio input
>level for max bars on ALC. For PSK31, i work
>with ~ 10 to15W max for 100W selectes with
>the control and "local" receiving give me an "acceptable"
>-24 to -28dB IMD.
>
>
>Julian, G4ILO wrote:
>> hb9ari wrote:
>>   
>>> Hello,
>>>
>>> As i use principally JT65A (snice ~ 2years),
>>> i've remarked transmit output power variations
>>> depending where the audio is located in the waterfall,
>>> as i'm not speaking English, it's difficult to explain correctly;
>>> if i'm ~ in the middle of the waterfall (~ 1200Hz)
>>> i get over 3dB in output power variations; for an expected
>>> 50W output power, between some tones of the JT65A
>>> modulation, the output level can vary from 20W
>>> to 60W; if i'm working away from the "middle",
>>> variations are lower and acceptable but most
>>> of time, "central" frequencies are used...
>>> I've always worked with this "problem" as i
>>> expect some AGC effect by the receiving side...
>>> I would appreciate to have an explanation
>>> of this effect.
>>>
>>>
>>>     
>>
>> This topic has been brought up before in the context of RTTY. The reason is
>> that there is no automatic level control in DATA A mode (or rather, there
>> is, but it is very slow acting to avoid causing IMD on PSK31 signals) so
>> there is no compensation for ripples in the roofing filter passband. It has
>> been suggested that the problem is less when using the 8-pole SSB roofing
>> filter as it has less ripple than the standard 5-pole filter.
>>
>> The output should not vary as much as you suggest while working within the
>> normal passband for JT65A operation so I'm wondering if you have correctly
>> adjusted the audio input level in DATA A to get 5 bars on the ALC scale.
>> This will not prevent the power varying for different tones during a
>> transmission but it should help maintain a constant average level when
>> working at different places within the passband.
>>
>> -----
>> Julian, G4ILO. K2 #392  K3 #222.
>> * G4ILO's Shack - http://www.g4ilo.com
>> * KComm - http://www.g4ilo.com/kcomm.html
>> * KTune - http://www.g4ilo.com/ktune.html
>>
>>   
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