Space Line quit broadcasting SW Radiogram and KBC at this point, because "the cooling system is not economical to run for just one transmitter".
Cause: Faulty sound card in audio source.
Once notified, they fixed it in about 4 minutes!
Good work, Woofferton Engineers!
Despite being notified on April 17, 2019, the problem has not been fixed.
"Our engineer is out of the country at the moment", they said.
No reply to my follow-up emails. The problem continues!
This fault degrades reception, and severely degrades reception using AM Sync or SSB detectors (resulting in high amounts of "rumble").
Update: November 8th, 2019. Still hasn't been fixed.
Update: September 24, 2022. WINB 9265kHz was observed to be jumping off-frequency. See image at right.
This suggests the synth used to generate the 9265kHz carrier urgently needs repairs or replacement.
Update: October 15, 2022. WINB appears to be overmodulating during the Shortwave Radiogram program. See image at right.
Also: October 15, 2022. The severe carrier phase noise has not improved. See image at right.
To paraphrase the words
of an Engineer:
"Good AM shortwave reception
requires
AM sync detection. To not fix a high carrier phase noise problem is JUST
DUMB."
Above: Zoomed in spectrum, showing high phase noise.
Above: November 8th - Close-in carrier phase noise.
Above: Sep 24, 2022. The WINB 9265 kHz transmitter jumping off-frequency by at least 50kHz.
Above: Oct 15, 2022. The WINB transmitter appears to be overmodulating - generating harmonic sidebands.
Above: Oct 15, 2022. The WINB 9265kHz carrier still has high phase noise.
Notified WRMI May 4 by email. No reply.
Notified WRMI May 9 on Facebook (twice!). No reply.
Emailed WRMI QSL address May 11. No reply - except for the alligator QSL!
Emailed WRMI GM Jeff White May 11. Still no reply.
Finally, I directly emailed a WRMI Engineer (Bob) - who told me the sad story of modern shortwave broadcasters.
The problem can't be diagnosed until around June 20.
The problem may relate to weak PA and driver tubes.
September 25, 2019 - Statement from above Engineer: "Nothing was done to anything at WRMI".
The distortion continues...
UPDATE further down the page on 14/01/2023.
Above: Audio envelope on music then speech.
Above: Single MFSK tone, showing distortion (AM Sync Demod).
Above: Waterfall spectrum showing splatter
(frequency doubling due to asymmetric distortion).
Above: Comparison to a clean signal.
Happens on station ID and program audio.
Maybe excessive drive level from the playout system? (should be an easy fix)
Distortion sounds worse than normal peak clipping (wideband - noise-like, not harmonic).
This does NOT sound like processor distortion.
This appears to be happening before the processor, as it is limited to processor bandwidth.
This issue was reported to the above Engineer, who appeared to dismiss it.
More data will be gathered...
Sounds like overmodulation, with simultaneous carrier phase modulation.
Probably due to overmodulation or PA/Modulator linearity problems.
Sounds very bad on SSB or AM Sync, and better on a normal AM detector.
NIST have been informed by email. No reply as of June 10, 2019.
* Update: Some of the WWV transmitters had maintenance
during 2021.
KBC 9925kHz
KBC program due to start at 0000UTC started 7 minutes late at 0007UTC on a backup transmitter.
Transmission appeared to be back to normal at 0026UTC.
Some momentary modulation dropouts occurred during the program, but were only fractions of a second long.
Overall, a very fast response to a transmission problem.
KBC 5960kHz
Transmission appeared to be back to normal at 0025UTC.
Once again, a very fast response to a transmission problem.
KBC 5960kHz
Once again, a very fast response to a transmission problem... (I am told "a transmitter arc")
But this is happening too often!
No longer can I say "Never a problem at Nauen"...
This 29Hz signal is present continuously.
More data was gathered:
Confirmation 1: Recording via Twente WebSDR shows 29Hz sidebands.
Confirmation 2: Recording by a 3rd party using a GPS locked FlexRadio also shows 29Hz sidebands.
Confirmation 3: Multiple IQ recordings of the sign-off of 5850kHz and 9955kHz were viewed using Spectrum Lab, and show the 29Hz sidebands disappearing as soon at the transmitter shuts down. This proves the signals are not interference.
A retired Continental Electronics Engineer was
asked about this issue, and suggested it might be due to blower vibration,
due to it's "almost synchronous" frequency of 29Hz (60Hz mains).
Above: Waterfall spectrum of 5850kHz captured using a Flexradio SDR showing 29Hz sidebands.
Unclear whether the midrange buzzing is also phase modulation.
WRMI were contacted (via Bob) on 23/09/2019, but are denying there is a problem.
More data was gathered:
Multiple IQ recordings of the sign-off of 5850kHz and 9955kHz were viewed using Spectrum Lab, and show the 29Hz sidebands disappearing as soon at the transmitter shuts down. This proves the signals are not interference.
A retired Continental Electronics Engineer was asked about this issue, and suggested it might be due to blower vibration, due to it's "almost synchronous" frequency of 29Hz (60Hz mains).
Update Oct 15, 2022: The
audio buzz problem appears to have been fixed relatively quickly. The 29Hz
phase modulation is no longer present, but there is hum at 60Hz and 120Hz
which appears to be phase modulated - or perhaps a mix of AM and PM.
Above: Waterfall spectrum of 9955kHz showing 29Hz and 58Hz spectral lines
Above: Waterfall spectrum of 9955kHz at signoff.
This has been seen for at least a few weeks now.
At first, a demodulator DSP code problem was suspected. Then the IQ data was checked, and the FM was clearly visible.
Then the KiwiSDRs were suspected, but three different KiwiSDRs (2 in USA, 1 in UK) all showed the same synchronized wobble on the same signal at the same time. This can't be a KiwiSDR bug, and can't be from propagation either...
The only possible conclusion is the Nauen 5960kHz carrier has a slow (0.5Hz) frequency wobble of something like 1.5Hz peak-to-peak deviation.
More proof:
The fault was first seen on KBC 5960kHz on September
15th.
Two more SDR types were used for comparison.
The fault was seen on Nauen 15715kHz by two other
people.
In the UK using an Icom IC-7300, and in the USA
using an SDRuno. Pics to the right:
Nauen have been contacted, and are investigating.
November 3rd: Nauen have fixed the problem!
November 11th: Confirmed - Nauen "replaced the control transmitter/unit".
Above: Three IQ recordings from two USA and one UK KiwiSDR, all showing synchronized FM wobble on 5960kHz.
Above: Close-in carrier spectrum of 5960kHz, in Spectrum Lab.
Above: Nauen 15715kHz at 1405UTC October 22, from an SDRUno in the USA.
Above: Nauen 15715kHz at 1420UTC October 22, from an IC-7300 in the UK, in Spectrum Lab.
Above: Nauen 15715kHz at 1352UTC October 22, from a USA KiwiSDR, in Spectrum Lab.
Above: Nauen 5960kHz at 0014UTC November 3rd, from a USA KiwiSDR. The carrier is now stable! Only ionospheric doppler shift remains.
Problems:
- Modulation was massively distorted, trashing the entire program and Ham-DRM data. Sounded like a severely overmodulated FM STL [Studio-Transmitter Link]. Anything other than quiet audio turned into something resembling white noise. Strong high frequencies seemed to make the problem worse.
- Modulation had no bass below 150Hz, except for a high hum level. The hum appears to indicate a badly maintained transmitter (power supply capacitor or rectifier problems). A 150Hz highpass filter is unacceptable on a music program.
- Program beginning was cut by 55 seconds, deleting the introduction.
- Poor frequency co-ordination by Media Broadcast GmbH meant that China was co-channel.
(Fee was waived by Media Broadcast due to the poor quality.)
Media Broadcast reported the problem to Yerevan. Yerevan replied that "there was no technical problem on their side." <- This statement is either a mistake, unqualified, incompetent or deliberately misleading.
Media Broadcast is aware of some distortion issues
at Yerevan, as are others.
- Failure was related to the filament connection on a tube socket in the modulator stage.
After repairs were made, the severe distortion
was fixed - but the distortion levels remained higher than before July
1st.
This will be entered as a separate problem below.
This problem began after 5850 was fixed on July 1st.
Sounds like some sort of nonlinearity or clipping in the modulation or playout system.
Given the previous failure listed immediately above, it is possible this issue is related. Correct - see below.
July 15:
https://storage.googleapis.com/dazman/misc/2021-07-15-RNEI19-clip.wav
AM waveform appears to have no positive modulation - only negative modulation.
Jeff White has been contacted a few times by email, but no replies have been received.
Severe distortion appears to be fixed again as of July 29th.
Distortion levels are now back to MODERATE again, as above.
Still no reply from Jeff White.
*** Update Aug 5th, 2021 ***
A series of low frequency sinewave ramps were added to the RNEI program to measure the system LF distortion characteristics.
Observed distortions were:
- LF clipping (a certain amount of this is probably from normal Optimod behaviour)
- Some asymmetric LF distortion (probably modulator/PA nonlinearity)
- Severe peak breakup above -6dBFS (system overload or instability)
- Random glitches on peaks (possibly due to #3)
Some possible causes may be:
- Excessive playout system level or EQ boosting
- Modulator distortion/instability or perhaps loss of negative feedback
Program level below -6dBFS:
| Freq | 40Hz | 60Hz | 80Hz | 100Hz |
| THD % | 63% | 38% | 24% | 18% |
Program level above -6dBFS (catastrophic waveform peak breakup):
| Freq | 40Hz | 60Hz | 80Hz | 100Hz |
| THD % | 169% * | 114% * | 41% | 28% |
Test conducted Thursday August 5th at about 0158 UTC.
*** Update Aug 12th, 2021 ***
No significant change - distortion is still present at about the same severity.
It's looking increasingly like this problem is due to a modulator instability issue, due to the way the distortion "snaps on" above a certain modulation level.
*** Update Aug 15th, 2021 ***
I was told by Engineer Bob that the filament connection on one modulator tube socket failed, and was temporarily repaired.
Since the temporary repair was made, the modulator has been showing distortion problems that suggest the filament is not receiving adequate voltage. (It might also be possible that the tube was damaged by an extended time running without an active heater, but this is not proven or known at this time.) This all means that the problem may continue for some time yet...
*** Update Feb 14th, 2022***
5850 transmitter was off-air for repairs.
*** Update Feb 17th, 2022***
Audible program distortion has greatly improved, possibly back to pre-fault values.
*** Update Mar 10th, 2022***
A ramped sinewave test shows the 5850 distortion has dramatically changed character. Instead of "snapping on" to severe levels, the distortion now increases linearly and gradually as the program level rises above about -5.5dBFS. LF tones above about -5.5dBFS program level still go into clipping, but the clipping sounds more normal and symmetrical.
*** Update Apr 7th, 2022***
5850 began distorting again - worse than previously.
Jeff White was contacted by email - and he replied!!
The fault was quickly identified, and the transmitter was shut down awaiting repair.
5850 was back on-air the next day (April 8th, 2022).
An update will be posted here when the modulation performance can be re-evaluated on music content.
*** Update Apr 14th, 2022***
The 5850 modulator appears to be fixed.
LF sinewave ramps added to the RNEI28 program appear to be basically undistorted, apart from some minor distortion that is probably normal Optimod bass clipping. These tests only went to -3dBFS.
Bass levels above -3dBFS
still appear to distort. This is probably due to a slightly excessive level setting in the system
(Sep 2022).
July 27:
https://storage.googleapis.com/dazman/misc/2021-07-27-0439UTC-5850kHz-AMsync.wav
Aug 5th test tones
Received audio:
https://storage.googleapis.com/dazman/misc/5850kHz-LF_Ramp-GA.wav
Original source audio:
https://storage.googleapis.com/dazman/misc/LF_Ramps.wav
Image: Sudden and dramatic waveform breakup is
visible as the program level exceeds -6dBFS
August 12 test tones
Received audio:
https://storage.googleapis.com/dazman/misc/2021-08-12-LF_Ramps-MO-AMsync.wav
Image: August 12th - 40Hz sinewave breakup above
-6dBFS program level.
Alabama SDR in IQ mode with standard AM envelope
detector (HDSDR).
Image: August 12th - 60Hz sinewave spectrum above
-6dBFS program level.
Missouri SDR in IQ mode with AM Sync detector.
NMC Pt Reyes
NMO Honolulu
NOJ Kodiak
NMN Chesapeake
NMC WEFAX - 2nd harmonic distortion, causing 3kHz
secondary tone on black (Multiple frequencies checked)
NMC Voice - Severe distortion on audio peaks (Multiple
frequencies checked)
NMO Voice - Severe distortion on audio peaks (Multiple
frequencies checked)
NOJ WEFAX - Severe distortion and possibly a frequency
error also
NMN Voice - Severe distortion on audio peaks (Multiple
frequencies checked)
All transmitter frequencies of each callsign/service appear to be affected equally.
The distortion is not just audible, it also generates a significant amount of splatter outside the assigned channel. The total width of the signal plus distortion appears to be about 7 or 8 kHz on the voice services.
NOAA were informed, and have passed the information on to the USCG.
USCG are working to fix the problems.
*** Update Sep 3rd ***
NOJ WEFAX appears
to be fixed.
NMC WEFAX, showing 2nd harmonic of 1.5kHz black
tone:
NMC Voice (IQ recording):
https://storage.googleapis.com/dazman/misc/69.27.184.58_2021-08-30T23_00_21Z_8764.00_iq.wav
NMN Voice:
https://storage.googleapis.com/dazman/misc/w3piesdr.ddns.net_2021-09-01T16_27_21Z_6501.10_usb.wav
NMN Voice, showing splatter:
NIST were contacted by email.
Problem was fixed within 1 day. NIST replied by email, saying the transmitter had been "retuned".
A good result.
https://storage.googleapis.com/dazman/misc/kiwisdr.itfais.com_2021-09-01T06_04_08Z_5000.00_sam.wav
Jeff White was contacted by email. No reply as
of Jan 16.
https://storage.googleapis.com/dazman/misc/kiwi.dol.la_2023-01-16T03_05_18Z_9395.00_sam.wav
9395kHz waterfall spectrum:
Jeff White was contacted by email. No reply as of Jan 16.
*** Update Jan 16th ***
9455kHz appears to
be fixed!
https://storage.googleapis.com/dazman/misc/scottgs.dynip.com_2023-01-14T21_56_19Z_9455.00_sam.wav
9455kHz waterfall spectrum:
