Radiofax: The Quest for ZSJ Cape Naval, South Africa (+ Updates)

Through my long journey to catalogue the remaining active radiofax stations, there has been a few rather elusive stations. Part of this category is ZSJ in Cape Naval, South Africa which I’ve never been able to hear and was doubtful was even in operation.

However, given the abilities given by KiwiSDRs, I decided to go hunting for ZSJ. However, this is not without its challenges – for one, the remote location is rather difficult to receive, with very few receiver options and the receivers that did exist frequently went offline due to connectivity issues. Originally, I thought it would be simple just to park on the frequency hoping to collect some results, but nothing was ever heard.

After a few days of not getting any result, I thought ZSJ was dead. But then, I came across the need to modify for better DX operation and decided to give it another go. This time, I was rewarded with success … of sorts. What follows illustrates my quest to receive ZSJ.

Note that the charts presented are a snapshot in time and are not updated. Charts are not to be used for navigation. Copyright belongs to the issuing entity, the South African Weather Service, with charts reproduced for documentary purposes to illustrate the technical characteristics of the transmission, formatting of the data within the charts and as proof of station activity, propagation and reception at the stated dates and times.


Attempting to receive ZSJ first began with finding a good candidate receiver, which at this time, meant one within Africa. Unfortunately, there is not much choice – TWR Africa and ZR6AIC but both have a habit of going offline from time to time. Better than nothing, I suppose, so I started to survey the four frequencies listed (4014, 7508, 13538 and 18238kHz). Of the four, I rarely ever saw any activity across any of them, which left me thinking that the station was offline.

By pure coincidence, I decided to use my new modified on 7508kHz and 13538kHz and … something emerged! I finally saw imagery but only on 7508kHz.

Reception was first achieved on 9th February 2019 at 0430UTC with the schedule as promised. Already evident is the existence of a gradient bar, short phasing/start/stop tones which makes this transmission similar to those of HSW64 Thailand and SVJ4 Greece. Unfortunately, the image quality was extremely poor with occasional horizontal noise bars due to overload of the KiwiSDR receiver and what appears to be horizontal smearing which suggests there are signal “echoes”. Normally multipath echoes result in short spreading of the signal, but this was long enough to be about the same height as the title text which is rather unusual. Charts transmitted also had a severe slant – no slant correction was yet applied on my “first day” reception.

The above was followed at 0500UTC by a surface analysis chart, with the echoes resulting in lines being followed by a clear region and then a “spread” version of the line. This suggests to me some “acoustic” echo … bad coupling of the fax machine to the transciever?

Leaving the script to continue collecting, another surface analysis was collected beginning at 1027UTC, slightly earlier than expected, suggesting that a human may indeed be in charge of the transmission of charts. It does, however, imply that the schedule provided by the NWS/NOAA is still current. Unfortunately, the connection broke a number of times resulting in loss of chart image, although the signal was extremely weak.

Another surface chart was received at 1528UTC on the same day – so that’s three surface charts of the four promised being received. Unfortunately, the Air Prognoses and Surface Prognoses from previous day don’t seem to be transmitted, and neither are the Antarctic Ice Limits as that appears to be seasonal. Again, very much there are strong echoes which cause the chart to take on a shaded appearance.

The next day, I came prepared with a slant correction of +100.0 just by pure guesswork. That improved things immensely, although could probably be further refined.

The same schedule is now received almost straight, on 10th February 2019 at 0430UTC.

Instead of receiving a surface analysis chart as with the previous day, at 0503UTC (three minutes late), an apology chart that is even longer than the actual chart is sent. Because of the clear bold text, the echo spreading can be seen to cause ghost images around the text – but it is clearly readable. As a result, ZSJ is a station I would consider unreliable.

A surface analysis was received but at 1529UTC instead – 10.5 hours after when it was expected to be received with no charts received in the interim.

I repeated the same reception on the 11th February 2019, with no real improvement in image quality for the 0430UTC schedule.

The same apology was transmitted at 0500UTC …

… and the surface analysis only appeared at 1540UTC, ten minutes late.

I tried to receive the station again over the next few days but was unable to decode any imagery at all. For five days, the station seemingly made no transmissions – or if it did, it wasn’t heard by the KiwiSDRs I used. I mostly used TWR Africa, but for assurance, I did add ZR6AIC to the mix with no change.

That is, until today on the 16th February 2019 when the schedule was once again received with echoes at 0430UTC.

The surface analysis received at 0500UTC, clearer than in prior days but still suffering echoes.

Troubleshooting the poor quality faxes proved to be rather interesting, as I had a known reference for when the signal would be on the air and went looking at many receivers to see if I could spot the signal. Ultimately, I could only find another receiver in Brazil which could hear the signal at any strength – India, Sri Lanka and Western Australia received nothing. Below is a look at the transmission from the TWR Africa receiver and a receiver in Paradinho, Brazil show the same characteristics –

It seems like the transmission has a wider than expected bandwidth with a lot of noise in the background. The tone frequency is slightly unstable, with some movements during the tuning tone period. A short start tone is followed by short phasing and colour gradient. However, what isn’t easily seen in the spectrogram is that the audio sounded as if it had significant echo.

This makes me suspect that someone’s basically “hung” an SSB transciever’s microphone in front of a fax machine’s speaker, resulting in the room acoustics and AGC of the transmitter wreaking havoc with the image quality. Add to this the variable HF transmission characteristics, and you get the kind of charts that are seen above.


The ZSJ station at Cape Naval, South Africa is alive, although somewhat unreliable. Charts are not always transmitted on time, with frequent apologies being transmitted. Image quality is extremely poor with “echoes” in the image and noisy signals regardless of receiver choice. The transmission does, however, have some ID and a gradient bar at the top, with short phasing/start/stop which implies equipment used to be similar to that used by HSW64 Thailand and SVJ4 Greece amongst others. However, it seems that they are transmitting the faxes probably by having a machine emit audio into a room and having a mic pick up that audio … resulting in the poor SNR and echoes observed.

Radiofax Station Status [Updated: 16th February 2019]

The latest update to the slant factors are as follows:

Callsign	Correction
--------------- ----------
CBM/CBV		-90.0
DDH/DDK		-12.0
GYA		+34.0
HLL2		-18.0
HSW64		-11.0
KVM70 		-4.0
JFX		 0.0
JJC/9VF		+3.2
JMH		 0.0
RBW41		-17.0
VCO		-24.0
ZKLF		+11.0
ZSJ             +100.0

The latest update to the station status are as follows:

Station Status as at 16th February 2019 (based on my observations)
----  ----------------- --------------------------------------------
ZSJ   South Africa      * Alive but Unreliable (This Post)
JMH   Japan             - Alive and Well (Published)
???   Chukota Peninsula ? Unknown, Not Heard
BMF   Taiwan            X Confirmed OFFLINE (see above)
HLL2  South Korea       - Alive and Well (Published)
HSW64 Thailand          - Alive and Well (Published)
JJC   Japan             - Alive and Well (Published)
9VF   Singapore         - Alive and Well (See Images Following)
GYA   Persian Gulf      X Reported Inactive, Not Heard
PWZ33 Brazil            ? Unknown, Not Heard
CB?   Chile             - Alive and Well (Published)
CFH   Canada            X Reported Inactive, Not Heard
VFF   Canada            ? Seasonal, Not Heard
VFR   Canada            ? Seasonal, Not Heard
VCO   Canada            - Alive and Well (Published)
VFA   Canada            ? Seasonal, Not Heard
NOJ   USA               - Alive and Well (Published)
NMC   USA               - Alive and Well (Published)
NMG   USA               - Alive and Well (Published)
NMF   USA               - Alive and Well (Published)
VM?   Australia         * Alive but (Temporarily) Unwell
ZKLF  New Zealand       - Alive and Well (Published)
KVM70 USA               - Alive and Well (Published)
SVJ4  Greece            - Alive and Well (Published)
RBW4? Russia            - Alive and Well (Published)
DD??  Germany           - Alive and Well (Published)
GYA   United Kingdom    - Alive and Well (Published)
???   Argentina         ? Unknown, Not Heard
LSB   Argentina         ? Unknown, Not Heard
CAN6D Chile             ? Unknown, Not Heard
OXT   Denmark           ? Unknown, Not Heard
ATP?? India             X Reported Inactive, Not Heard
5YE?  Kenya             ? Unknown, Not Heard
6VU   Senegal           ? Unknown, Not Heard
RTH   Uzbekistan        ? Unknown, Not Heard
JFX   Japan             - Alive and Well (Published)

HISTORICAL STATIONS from (Most Likely Inactive)
----  ----------------- --------------------------------------------
YMA20 Turkey            ? Unknown
R??7? Russia            ? Unknown
BAF?? China             ? Unknown
VLM   Argentina         ? Unknown
???   Argentina         ? Unknown
3MA?? Taiwan            ? Unknown
HM??? North Korea       ? Unknown, Not Heard
R??7? Ukraine           ? Unknown
CZW   Canada            ? Unknown
3SD   China             ? Unknown
LOR   Argentina         ? Unknown
BDF   China             ? Unknown
VNA   Vietnam           ? Unknown, Not Heard

I was able to verify 9VF relay for JJC was operative by reception through VN-SWL KiwiSDR – the below two partial faxes received in 60LPM on 16th February 2019 at 0825UTC in parallel on the two frequencies 16035kHz and 17430kHz.

Unfortunately, it seems that VMC/VMW remain unwell, continuing to show phasing “jumps”. Hopefully it will be fixed soon, in which case, I will write a post to cover it.

I’ve also made an edit to CBV/CBM as I’ve had some better luck at receiving it via but the unreliability of the receivers meant I could only get a few more faxes.

I will continue to hunt for signals from other stations, but I feel it highly unlikely I will be able to discover too many others.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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