HF ACARS (ARINC)

[MHZ]

May not be in the right forum here, but it was the closest I could find.
I am taking a fair stab that this is out of Guam. Just seems to be to strong for San Francisco which is the only other TX location for 8927 in the lists I have found.

The question is:
Why is there nothing being decoded in the PC-HFDL software? The tone of the digital signal changes often, yet can see nothing being decoded at all on the screen. Completely blank as you can see below.
What am I doing wrong? I tried moving off the center freq +/- 2k with no success either.

[Josh]

HFDL is very susceptible to a undesired tone on frequency, to the point of no decodes even for strong sigs. It looks like you have a fairly strong signal that is not HFDL in the passband, but I could be wrong. The sig in the pic you posted does not look like HFDL. The undesired sig could be local as in your domicile, or external. Also, try different IF modes (low IF and zero IF) and sampling rates as well as increased decimation to see if you can move the noise outside the passband of interest. You don't need 10MHz of spectrum displayed to copy HFDL.

My RSP is set to use low IF and decimation 32 with a resultant spectrum width of 300KHz. This, along with careful manipulation of the gain slider will get you best performance on hf as far as dynamic range and sensitivity at the cost of spectrum on display. The local noise issues you have to deal with yourself.

[MHZ]

HFDL is very susceptible to a undesired tone on frequency, to the point of no decodes even for strong sigs.

Ok thanks for that tip, never done HFDL before yet.

It looks like you have a fairly strong signal that is not HFDL in the passband, but I could be wrong.

If you mean the signals up on 9350 and thereabouts, they were AM shortwave stations.

The sig in the pic you posted does not look like HFDL.

Possible! Although I have never heard anything before on 8927 here. As this was around 3/4AM here, there was nothing running that would have been causing the noise.
I keep a pretty close ear on 8-9 MHz as that is were most of the LDOC freqs lay for this area, which I listen to quite a lot. I will take a listen at different times through out today and see if it is present.

You don't need 10MHz of spectrum displayed to copy HFDL.

Not sure if this is a tip or a comment, I was only running 2 MHz at the time, which is typically what I run it at. Only deviate from that in the VHF aviation band, or when I am hunting stuff on VHF/UHF.

My RSP is set to use low IF and decimation 32 with a resultant spectrum width of 300KHz.

Yes, same here Low IF, although as you can see from the pic my dec was at 1, which is default, I will try your suggestion and see how it works, thanks. As for noise, I am fortunate enough to live in the country in a farming area, as such I have very little man-made noise to contend with. Only noise here is the TV inside when the old man watches it of a night-time and now and then the water pump - but both only effect certain freqs. I am confident once I relocate my long-wire the tv will no longer be a problem. I did have a dipole running off the house near where the tv is located and the noise was horrendous across all HF bands, rendered HF totally useless while it was on.

Oh and I forgot to mention the electric fence, it only effects MW and LW bands though, and is rather band on certain freqs in LW band, it favours 77.5 KHz unfortunately

[Josh]

That 77.5Kc sig and multiples is likely the switching psu for the fence system. Same for pc psus. Shame these things are seldom filtered to any degree and are attached to sometimes miles of antennae in the case of lectric fence.

Anyway, you could park the setup on another HFDL freq to verify you have the sound card and decoder and everything connected properly, if you haven't decoded before. My usual HFDL session is two or three HFDL freqs and a ALE freq via virtual receivers, all plumbed to their respective decoders.

[MHZ]

Just listening now at 0747 Eastern Aust Time (2147z) and it is still there, a lot weaker than earlier on, now between S6 and S7.
In respect to decimation (which I must admit I am not fully aware of how it functions), up to 8 I can still hear it, above that it is gone.

I have uploaded a audio file below of what I am receiving. You can see that the data changes and towards the end there is a definite burst of data.

https://drive.google.com/open?id=1B7F7deey7Q7wyjuy-oPZhkNfazBNqyJP

[Josh]

I passed the sig you posted to a decoder and it was off freq, also the sig was halfway out of recorded passband so no decode. Also, the interference is pretty much right atop the sig of interest and may or may not have hindered copy.

[MHZ]

Ok thanks.
With HF Acars is it the same as Weather Fax, 1.9 below carrier freq? Or are the listed freqs the correct ones to use?

[Josh]

That splains it. HFDL is carrier freq as listed, FAX is 1.9 lower.

[MHZ]

No, I was on the listed freq of 8927, I was just asking if you would do the same 1.9k shift as with WeFax.

[Josh]

Odd, looks like you had 3kc of filter bandwidth and tuned to 8927 usb but still half the signal was cut off by the lowpass end of the filter.

[MHZ]

I may have named this topic wrong, not sure. Is HFDL and HF-ACARS the same animal? This freq is for HFDL ARINC.

[Josh]

I may have named this topic wrong, not sure. Is HFDL and HF-ACARS the same animal? This freq is for HFDL ARINC.

Typically when mention is made of ARINC in hf decoding circles they mean ARINC 635 aka HFDL. And the Utility forum is more along this topic than the FAX forum is.