Posted by
Dr. William J. Schmidt, II on
Oct 21, 2020; 2:48pm
URL: http://elecraft.85.s1.nabble.com/Amplitude-variation-on-K3S-with-JT65B-tp7665870p7665872.html
I have a K3 and a K3S at my Caribbean station... I see the same behavior on
my K3S but not on the K3. I've calibrated it several times but have not
diagnosed it past that. I've seen the power vary by as much as 50% at
times.
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-----Original Message-----
From:
[hidden email] <
[hidden email]> On
Behalf Of Conrad PA5Y
Sent: Wednesday, October 21, 2020 6:50 AM
To:
[hidden email]
Subject: [Elecraft] Amplitude variation on K3S with JT65B
Hello while I wait for feedback from the (no doubt overwhelmed) Elecraft
support I thought that I would ask the group about a problem that I have
with my K3S.
When I run JT65B and even to a lesser extent FT8 I see unacceptable
amplitude variation on both the 6m output and the transverter output (on
28MHz). If I put my E4406 Spectrum analyser on peak hold with a narrow span
and 10Hz RBW I see amplitude variations of a little over 1dB on the
modulation tones across the passband.
To save time.
1. On the ALC meter I have 4 bars lit up with the 5th occasionally
flickering - the audio drive level is correct; it is not an ALC issue
2. I calibrated the TX drive - the effect is observed at 1mw, 5W, 50W and
100W on 6m.
3. I am using DATA A so no TX EQ or compression
4. The audio has from WSJT-X been measured on a UPV audio analyser and
there is less than 0.1dB variation when using a UMC404HD sound card
5. The effect is observed with both Line input drive and the UMC404HD
soundcard and the internal K3S codec
6. My old TS2000X does not exhibit more than 0.1dB amplitude variation
with the same sound card providing audio and the same test setup
7. I have verified the amplitude variations at RF with a diode detector
and an oscilloscope
8. The effect is clearly visible on several power meters
9. This AM causes some spectral re-growth, although this is tolerable
So given all that I am beginning to wonder if the problem is due to filter
ripple in the standard K3S 2.7kHz filter? I cannot think of anything else. I
was considering buying an Inrad #718 filter.
This is very critical for EME when signals are weak at the RX side, if you
have amplitude variations and you are at the threshold of detection at the
receiving station this can cause decodes to fail. This is more important on
6m EME than 2m where I have more margin.
I think that this will be quite common, has anybody else got a K3S and the
equipment to check and verify my observations?
73
Conrad PA5Y
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