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Author Topic: Does anyone have a spare BT80A-RF2 ?  (Read 2561 times)

H4rry

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Does anyone have a spare BT80A-RF2 ?
« on: January 24, 2017, 12:11:04 PM »

Does anyone have a old BT80A/RF2? (Or know where I could source one? no listings on ebay at the moment) I need one in order to prove a concept that a local AM radio mast is causing interference on the telephone line.

The latest RF3 is no good for the test as it lets through DSL signals which overlap the same frequency as AM radio and therefore will not filter out the RFI.
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burakkucat

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #1 on: January 24, 2017, 04:02:22 PM »

Welcome to the Kitz forum, H4rry.  :)

Hmm . . . Sorry but I do not have one in my grotto.  :no:

A year or so ago I remember assisting Walter in sourcing such a device and eventually an eBay seller was found.

Ah, ha! Here's one:)
« Last Edit: January 24, 2017, 04:27:45 PM by burakkucat »
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4candles

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #2 on: January 24, 2017, 04:18:15 PM »

Good work b*cat.  :)

The seller is lucky to find a buyer as

"GPO Strowger Block Terminal 80b used to help Filter out Radio Interference"

doesn't mention 'RF2'.

Still, the photo confirms it's the right article.
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burakkucat

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #3 on: January 24, 2017, 04:25:29 PM »

Good work b*cat.  :)
. . .
Still, the photo confirms it's the right article.

It was a case of tingles in the whiskers, coupled with the thought that I had recently seen one listed, that prompted me to scrutinise the image.  ;)
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H4rry

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #4 on: January 24, 2017, 05:20:28 PM »

Thanks burakkucat you are a star! :)

If anyone else has (or knows of) one immediately available please let me know as the auction still has 8 days to run.

Thanks again
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burakkucat

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #5 on: January 24, 2017, 05:28:33 PM »

Thanks burakkucat you are a star! :)

  :blush:
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ejs

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #6 on: January 24, 2017, 06:08:19 PM »

What about using an ordinary DSL microfilter? The phone socket on a microfilter would have all the DSL (and AM radio) frequencies filtered off.
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H4rry

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #7 on: January 24, 2017, 06:48:36 PM »

I thought the same thing ejs

I tried a microfilter but still got the interference. There's no DSL on the line so I wondered whether the microfilter, being passive, needed an active DSL service to work. As such, I've also placed an order for a high quality active microfilter (xf-1e) (which contains a transistor based ciruit powered by the line) in order to try again and see whether that will filter out the AM radio station (which incidently is GOLD on 1548KHz).

Between that and an RF2 I'm hoping one or the other will work, otherwise it's back to the drawing board scratching my head.
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tubaman

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #8 on: January 24, 2017, 07:44:11 PM »

Have you tried a different phone on the line, as it could be the phone circuitry that's picking up the AM rather than the line itself.
 :)
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H4rry

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #9 on: January 24, 2017, 08:25:53 PM »

Im sure tried 3 different phones, connected to test socket, 95% of the time it's a perfect line, then all of a sudden sounds like tuner control being twisted and gold radio coming and going. I am now on the 5th BT engineer visit that just runs a test on the line at times when line is fine and leaves marking the case as resolved. Decided to take a more hands on approach before calling BT out again.
« Last Edit: January 24, 2017, 08:59:59 PM by H4rry »
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NewtronStar

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #10 on: January 24, 2017, 09:19:36 PM »

Had a look in my large Broadband cupboard and have two BT80A RF3 units and quite unsure why the RF2 would be any better than the RF3 in your case as both have a ferrite toroid with windings inplace for ADSL and VDSL frequency range

You want all the DSL signals to reach your modem and not to be filtered out I would not even use the BT80A RF2 or RF3 if you already have a SSFP installed at the master socket
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H4rry

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #11 on: January 25, 2017, 05:39:50 AM »

I don't have a modem it's just a plain pots line without DSL.

The RF2 filters out more than the RF3 so hoping it will filter out the AM radio sounds that are coming through on 1548khz which the RF3 may let slip through since DSL frequency range also covers that frequency. Its just a theory which is why I'd like to try it out and see.

I've just sourced an RF2 and placed the order.

Fingers crossed the RF2 or microfilter will work.
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burakkucat

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #12 on: January 25, 2017, 06:04:03 PM »

Essentially you would require a low-pass filter suitable for the range DC - 4 kHz. For added efficiency, a parallel LC tuned circuit (1548 kHz) could be added as a shunt across the pair.

fresonant = (2 Pi (LC)-2)-1      (1)

Rearranging (1) gives . . .

LC = (fresonant2 4 Pi2)-1      (2)

Substituting known values into (2) . . .

LC = 1.057 x 10-14 Henry Farad
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H4rry

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #13 on: January 25, 2017, 07:26:11 PM »

:) That's going beyond my understanding burakkucat.

However, if my efforts of introducing the components I've ordered don't resolve the problem I will make a cup of tea, pull out my old physics and electronics reference books, pull up comfy chair and try and understand your equation for using a low-pass filter with a shunt.

This forum is great :)
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tubaman

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Re: Does anyone have a spare BT80A-RF2 ?
« Reply #14 on: January 26, 2017, 09:22:28 AM »

This is odd as a normal DSL dongle should fix this as it should filter out everything above approx 4KHz.
Admittedly the cut-off won't be perfect but it certainly should be killing frequencies as high as 1548KHz.
 :hmm:
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