[Elecraft] JT65A output power variations.

[hb9ari]

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
>
>