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SpanishSailor
Beginner
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Message 1 of 6

BT Smart Hub RFI immunity from amateur radio transmissions

I'm a radio amateur and recently started experiencing broadband drop outs when transmitting with low power (5 watts) around 7MHz (40m amateur band). My aerial is located 50m away from the house on the opposite side to the drop cable.

In order to minimise RFI from common mode currents I use several filters on my radio equipment and have also added ferrite chokes to the cabling for the BT Smart Hub but the drop outs still occur.

Can anyone recommend a VDSL router that has good RFI immunity that's compatible with BT Broadband?

This has not been a problem in the past - maybe the modem has negotiated different VDSL frequencies?

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Keith_Beddoe
Distinguished Sage
Distinguished Sage
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Message 2 of 6

Re: BT Smart Hub RFI immunity from amateur radio transmissions

@SpanishSailor 

You would not be able to stop radio transmissions at 7MHz from affecting a VDSL connection, no matter how hard you try, because the signal will be induced in the phone wiring and external network.

Here is the spectrum graph of both ADSL and VDSL.

VDSL extend up to 12MHz.

Either operate on a higher band, or hope that you can get FTTP at some time in the future.

adsl vdsl spectrum.jpg

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Paul608085
Aspiring Expert
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Message 3 of 6

Re: BT Smart Hub RFI immunity from amateur radio transmissions

@SpanishSailor 

Have you been able to prove whether the RF is getting in to the line or the hub?

One way to do this might be to put the hub in a metal tin of wrap it in foil. Just for a very quick test of course, else it will quickly overheat - but it might help to ascertain if you are looking in the right place.

Also, you said that you put chokes on the cables to the hub - does this include the DC power cable? Mine has a choke built in at the PSU end to filter out interference from the switched mode supply, but I added another immediately before the plug to the hub.

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SpanishSailor
Beginner
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Message 4 of 6

Re: BT Smart Hub RFI immunity from amateur radio transmissions

I assembled a simple notch filter that is resonant around 7.150MHz on a short length of cable terminated with a RJ11 plug. This is plugged into a twin RJ11 adapter on the Openreach wall plate so that the filter is in parallel with the modem cable.  Works great - no more drop outs when I transmit on 40m.

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Paul608085
Aspiring Expert
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Message 5 of 6

Re: BT Smart Hub RFI immunity from amateur radio transmissions

Has this affected your hub's sync speed at all? I would guess that if you are filtering out some of the frequencies then your speed would drop - al least a bit?

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SpanishSailor
Beginner
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Message 6 of 6

Re: BT Smart Hub RFI immunity from amateur radio transmissions

Tested speeds before and after. Download speed decreased slightly from 36.5Mbps to 34.2MBs, upload speed unchanged at 8.95MBs.

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