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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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4th Apr 2017, 10:18 pm | #1 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
Posts: 2,552
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Wireless FM Intercoms Interference
Sorry if this is in the wrong section, please move if so.
I collect Wireless FM intercoms, some from about the late 60's to early 70's & 80's. The 60's & 70's ones all suffer from mains(?) buzzing but the 60's one, more so. The mid 80's ones are acceptable for intercom use but, even then, when used as a Baby Monitor the even lower level of buzz can still be disturbing. I don't think they're all faulty (what's the odds) so I can only assume that the 60's ones were designed in the days when the mains supply was 'cleaner' ? and today's supply is crowded and hence more buzzing noise. Or am I way off the mark in my thinking ?
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! |
4th Apr 2017, 11:33 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,947
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Re: Wireless FM Intercoms Interference
I suspect you're right, and the increased level of digital hash and SMPSU nasties is causing problems.
The supply in the 60s wasn't necessarily 'cleaner' but the noise profile was very different to today. |
5th Apr 2017, 10:36 am | #3 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Wireless FM Intercoms Interference
Is part of the problem old electrolytics in the PSU drying out and so having raised ESR? They may still measure OK for capacitance and so can still reduce ripple, but the ESR puts a buzz on the supply rail.
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5th Apr 2017, 3:34 pm | #4 | |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
Posts: 2,552
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Re: Wireless FM Intercoms Interference
G8HQP Dave
Quote:
I've decided to change the caps in an early 70's Realistic model which has one of the 3 unit set that has more of a buzz that the other 2. I'll be undertaking this tonight and I'll report back. Cheers for now.
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! Last edited by camtechman; 5th Apr 2017 at 3:40 pm. |
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5th Apr 2017, 6:51 pm | #5 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Wireless FM Intercoms Interference
I had a set (Realistic, mid 1980s) which worked fine on an extension lead or a radial circuit but wouldn't work on a ring circuit.
I think this was quite a common problem as most came from the USA, modified for our voltage, but couldn't cope with ring wiring. |
5th Apr 2017, 8:27 pm | #6 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Wireless FM Intercoms Interference
Was there something wrong with your ring circuit?
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5th Apr 2017, 10:36 pm | #7 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,642
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Re: Wireless FM Intercoms Interference
I once had a Realistic FM intercom, it worked OK here. I wasn't aware of any buzzing, but it was a while ago before the current interference levels.
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5th Apr 2017, 10:50 pm | #8 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,687
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Re: Wireless FM Intercoms Interference
I had an 'Eagle' set of these things back in the early 1980s, for communicating between the shack (shed at the bottom of the garden) and house. They worked fine, until the fluorescent lamp in the kitchen was switched on, then they went dead.
I can only think it was the power-factor correction capacitor in the fluorescent lamp shunting the speech path.
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10th Apr 2017, 12:26 pm | #9 |
Nonode
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
Posts: 2,552
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Re: Wireless FM Intercoms Interference
Sorry that I haven't replied before but I have now replaced all the electrolytics and the buzz still persists but one other problem has disappeared : the call tone/signal is clear, instead of it sounding like a fuzz box on a guitar.
Following the suggestions about a possible problem with the ring circuit I decided to try the units out on various other sockets around the house and got a variation in buzzing levels, in fact one combination: one unit in the utility room & the other in the upstairs box room, all buzzing ceased ! As this seems to raise a similar problem that I've had for a long time: interference to radios on MW, both in the kitchen & living room, I'm wondering if the Intercom & Radio problem is linked to problems with the ring main, or more seriously, to the whole mains system ?! I'll follow up later....but this may take some time. Watch this space.
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When I die, please don't let my Wife sell my collection for the amount I told her I paid for it! |