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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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15th May 2020, 10:37 am | #1 |
Heptode
Join Date: Oct 2006
Location: Leeds, West Yorkshire, UK.
Posts: 598
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Tandy/Realistic FM wireless intercoms
Does anyone have any experience of these devices, whether good, bad or indifferent ? I remember seeing them in the Tandy catalogues for years in the 1980s with the seemingly bold claim that all you had to do was plug in to the mains, switch on and you were in business, so to speak. If I've got it right, the technology was something like an FM transmission superimposed on the mains cabling, however that worked. I particularly remember that it was possible to use the sets not only within your own house or office, but also with your next door neighbour, provided there was some degree of electricity supply commonality.
I've neither seen nor used any such device and I don't know if the likes of Eagle and Sterdy make them. Obviously, Tandy disappeared years ago. Many thanks. |
15th May 2020, 11:06 am | #2 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,586
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Re: Tandy/Realistic FM wireless intercoms
Yes, we had some Tandy ones for a while. There are so many other signals superimposed on the mains now - powerline networking adaptors, etc - that I'm not sure such simple 'analogue' devices would be able to function any more.
They did depend on both, or all stations, being on the same mains phase. |
15th May 2020, 11:31 am | #3 |
Heptode
Join Date: Oct 2006
Location: Leeds, West Yorkshire, UK.
Posts: 598
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Re: Tandy/Realistic FM wireless intercoms
Thankyou Sirius. I thought I remembered something about being on the same mains phase.
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15th May 2020, 8:07 pm | #4 |
Heptode
Join Date: Aug 2009
Location: High Wycombe, Bucks. UK.
Posts: 811
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Re: Tandy/Realistic FM wireless intercoms
I have an Altai branded one, probably much the same internally as the Tandy ones. It uses low frequency RF transmission. I think mine can be switched to 150KHz or 250KHz to avoid interference or conflict with your neighbours. Both of these frequencies are in the long-wave band. I can pick up the intercom on a normal domestic LW radio in the same room, even though ithe radio is AM and the intercom is supposed to be FM.
Other than the above reception test, I haven't actually used it as an intercom, since I only have the one base unit. A pair is required. I'm guessing that these intercoms should still work despite much more mains-borne noise these days. FM is supposed to be quite good at rejecting interference. |
15th May 2020, 8:40 pm | #5 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Tandy/Realistic FM wireless intercoms
I had one. They didn't like ring circuits (distorted sound to the point of uselessness) but would work fine on an extension lead.
That was in the days of rewireable fuses. With MCBs and RCDs in circuits there might be more obstruction to the signal. As well as the speaker versions there were one or two handset-style ones available. |
15th May 2020, 9:12 pm | #6 |
Heptode
Join Date: Oct 2006
Location: Leeds, West Yorkshire, UK.
Posts: 598
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Re: Tandy/Realistic FM wireless intercoms
It was probably quite a good idea, at least initially, to use the mains wiring for something other than moving electricity around and at no added cost. Not unlike the early American telephone networks that used the barbed wire fences around the farms and ranches as transmission cables. Certainly not ideal but better than nothing.
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15th May 2020, 11:03 pm | #7 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,117
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Re: Tandy/Realistic FM wireless intercoms
I believe that electricity consumer meters are or were opaque at around 150kHz. This means you are isolated from your neighbour's mains intercom
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16th May 2020, 12:56 am | #8 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,342
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Re: Tandy/Realistic FM wireless intercoms
I've still got 2 pair of them and used them from house to shed until a few years ago.
They had to be used on the same phase and wouldn't work across different phases of a three phase system so it was possible to work the house next door, depending on which phase they were connected to. Modern equipment, with filters, plugged in around the house does diminish their usefulness to the point of being unusable now. And yes, they superimposed the audio onto a carrier that was superimposed on the mains. There were circuits in some of the older mags like Practical Electronics from memory where you could build your own. |
16th May 2020, 8:03 am | #9 |
Heptode
Join Date: Oct 2006
Location: Leeds, West Yorkshire, UK.
Posts: 598
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Re: Tandy/Realistic FM wireless intercoms
It would be a nuisance if you'd bought a set for something other than in-house communication to find that your individual electricity supplies weren't on the same phase.
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16th May 2020, 8:18 am | #10 | |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,988
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Re: Tandy/Realistic FM wireless intercoms
Quote:
John.
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16th May 2020, 9:30 pm | #11 |
Octode
Join Date: Aug 2005
Location: Saltburn-East, Cleveland, UK.
Posts: 1,786
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Re: Tandy/Realistic FM wireless intercoms
Hi, there is currently a pair of the Tandy/Realistic units that you mention listed on eBay here
I have no association with the seller and have included the link for the purpose of interest only. Andrew |
16th May 2020, 9:37 pm | #12 |
Heptode
Join Date: Oct 2006
Location: Leeds, West Yorkshire, UK.
Posts: 598
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Re: Tandy/Realistic FM wireless intercoms
Thanks for the heads up Andi. At that price I believe I'll pass but it would be interesting to see how well they perform these days.
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23rd May 2020, 10:11 pm | #14 |
Heptode
Join Date: Jan 2009
Location: West Lothian, UK.
Posts: 762
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Re: Tandy/Realistic FM wireless intercoms
I sold mine two years ago for £9.99.
They worked ok in my house and on 25 metre extension to garden shed but we don't have any powerline digital stuff. The buyer initially claimed they were non-functional although did not return them for testing.
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25th May 2020, 3:17 pm | #15 |
Tetrode
Join Date: Feb 2007
Location: Fordingbridge, Hampshire, UK.
Posts: 56
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Re: Tandy/Realistic FM wireless intercoms
Have an old device here as well and strangley it can be received in the long wave band as well(!) - although the radio has to be pretty much next to the device or nothing is received. The device is branded as a national VK233 and I think maybe from the 80s. Unfortunatly mine do not seem to be working all that well - the range is so bad it only works from within the same room (I do have a second device); try plugging in one upstairs and one downstairs and nothing - !
Does anyone know why it should be quite *that* bad? I mean I wouldn't expect mircacles from such an old device, but not doing anything from upstairs to downstairs seems to indicate some sort of fault to me. ljones Last edited by ljones0; 25th May 2020 at 3:23 pm. |
25th May 2020, 5:56 pm | #16 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Tandy/Realistic FM wireless intercoms
A combination of ring circuits, and MCBs/RCDs in modern consumer units, blocks the signal.
Try fitting the devices to lighting circuits which are radials and might not be on RCDs. |
25th May 2020, 8:43 pm | #17 |
Heptode
Join Date: Oct 2006
Location: Leeds, West Yorkshire, UK.
Posts: 598
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Re: Tandy/Realistic FM wireless intercoms
It seems as though modern domestic electrical wiring has left behind the FM wireless intercom.
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25th May 2020, 8:55 pm | #18 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Tandy/Realistic FM wireless intercoms
Yes - here in the UK they once sort-of worked OK on ring-mains. But I remember that even back in the 1970s they were 'marginal' on the standard US one-15A-radial-per-room power-wiring.
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29th May 2020, 12:32 am | #19 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
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Re: Tandy/Realistic FM wireless intercoms
Quote:
Anyway, here's a hopefully legible copy of that circuit for interest. Inverters are 4069, audio amp is LM386 and IC3 is LM567.
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29th May 2020, 8:10 am | #20 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Tandy/Realistic FM wireless intercoms
This is a mains programme distribution unit, from Public Address Handbook, Vivian Capel. Separate sender and receiver.
A two-stage modulator which modulates the collector current of the rf oscillator. Should be at about 100 kHz. There is no frequency stabilising. Applies the output to live and earth (not neutral) as this avoids the effect of heavy shunting loads in the circuit. (This dates from 1971 when RCDs were either unknown or certainly not in common use.) A tuned circuit and diode detector in the receiver. "All components are standard except the oscillator coils which were specially wound." |