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Data Mode QRM on 30-metre (10MHz) band

30m is my favourite band for SOTA. Propagation is often very good and I can usually count on it for enough QSOs to qualify a summit with 5W to 10W CW and my EFHW only a few metres off the ground.

I tend to operate on or near 10.1175MHz. Yesterday, I think all four of my 30m QSOs were interrupted by a single 10- to 15-second burst of strong data centred on that frequency. Fortunately, all of my chasers all over Europe (several with weak signals) were patient enough to wait until the data transmission had stopped so we could complete our exchanges (thank you!).

I can’t say the mid-QSO data bursts were deliberate – maybe the data-mode operator couldn’t hear me. Or, is it some DM ops don’t actually listen by ear to a frequency before transmitting and just check their waterfall plot?

In any case, I thought EU countries had implemented the IARU Region 1 band plan recommendations with CW 10.100 to 10.130 and narrowband data modes 10.130 to 10.150. Is that not the case?

I will probably put the experience down to bad luck, but do other 30m CW ops have this or similar problems?

Hi Andy,
are you sure the digital transmissions were from an Amateur station? Although 30m is allocated as a primary allocation to the Amateur service (I believe), military stations from various countries have been known to “stray into” amateur bands. This could, of course, be some other interference of some sort as well - VDSL2 for example where the amateur band hasn’t been “notched out” when the engineer set up the connection.

As you say - 10.130 - 10.150 MHz is where we would normally expect AR digital modes to be in IARU Region 1.

Hopefully, the interference doesn’t come back but if it does, you need to find if it is local (i.e. VDSL2 or similar) or longer range (e.g. OTHR) interference or the worst-case DQRM (which I would hope is unlikely).

Good luck, 73 Ed.

No, we are secondary on 30 mtrs, Ed. We should stop transmitting if we suspect that we are causing interference to a “Fixed Service”, as they are primary. We’re less kind to Asian fishboats :slight_smile:
73
John VK4TJ

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Hi Ed,

No, with just my KX2 I’ld have no way of even telling what kind of digital mode the transmission was.

Re VDSL2, I’ve no idea how far VDSL2 can radiate on HF or what it ‘sounds like’ when received, but it occurs to me that, although I was at a remote location (not even farmhouses nearby), it is a wind farm (Kirkby Moor, G/LD-049) with two giant wind turbine towers within 100m of my position at the summit, So, maybe VDSL2 is used for comms with them.

I’ll have to visit more wind farms with my HF rig to find out!

73, Andy

Hi,

Digital modes with 15 second cycle times are 50 Hz wide, so the sound of one is quite distinctive. It’s an audio tone with a very slight warble. Also the timing is very accurate, commencing on the minute and subsequent 15 second multiples. The transmission is for 13 seconds nominally.

OTHR on the other hand sounds like a mad woodpecker and can cover up to 100 kHz. When there is a sniff of propagation these megawatt erp signals are loud. Not everyone who owns one cares about the notching of amateur bands.

There are other interferers but the FT8 and its cousins can be readily identified. Just listen to 14.074 USB if you want to hear what a bunch of these guys sound like. 10.036 MHz USB is where you will hear them on 30 m. Rarely do they go lower but often are up to 3 kHz above the dial frequency.

I can’t tell from your description what the interference was from. Perhaps get some more data before blaming other amateurs.

On my last activation the RADAR was so persistent I gave them a report.

73
Ron
VK3AFW

Did they acknowledge? :wink:

73,

Guru

:rocket: Yes, they shot an Ying Ji YJ91 Eagle Strike ARM at him :rocket:

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Since Ron has been posting here, I’d say they didn’t hit the target… Thanks God!

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I believe the ARRL maintain a web page with recording of different types of interference - it may be worth comparing what you hear with that. They certainly have one sort of over the horizon radar - of course if we are only secondary users and what you are hearing is a (e.g.) military station - you are by definition the Interference not him/her.

73 Ed.

There lies the problem especially when it’s a short (10s) burst and you’ve no idea if and when there will be another one. It’s not obvious if it’s a primary user, another amateur or even VDSL2 RFI from the nearby wind turbine.

My money is on the communications to / from the turbine. We have zillions of the beasts around here and the qrm can be deafening - unless there is high pressure of course :grimacing:

In VK3AFW’s reply, that should have read “10.136”, of course. Unfortunately, current events have rendered the “gentlemen’s agreements” obsolete. DXpeditions now pack along a variant of FT-4 or FT-8, and set up camp wherever they bloody well feel like it. Their chasers can and are spread over 3 to 5 kHz, typically upward from the DX. Even couch potato FT-8 & FT-4 users seem to have established “alternate” frequencies. Here in VK, 10130 is lost to us, for example, as more digi-heads set up camp on 10131. John, VK4TJ.

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