Demystifying this antenna

[SurreyNick]

I have attached some pictures of a 'Super Signal Antenna' which I spotted for sale online. It has, I believe, two windings (there are 4 wires coming from the windings) and also what appears to be a capacitor built into the circuit. But I can't make sense of it.

1. If it's an antenna why are there 2 separate windings?
2. The terminal to which one end of the capacitor is connected goes to where in the receiver circuit? On the flip side of the antenna board it's soldered to a socket labelled up 'Replace Tubes'
3. How does the winding arrangement work? The two trailing wire leads are connected to just one winding (yes?), so what's the other one with the capacitor[?] for and how does it relate to the other winding?

I'm confused.

Thanks

Nick

[G6Tanuki]

I'm supposing that this is from a US 'midget' universal AC/DC design.

The main winding is designed to serve as the front-end tuned-circuit in the style of a 'frame aerial' and connect between ground and grid of the first valve.

The second winding is connected [via the capacitor] to allow an optional external 'throw-out' wire antenna between the appropriate terminal and chassis.

The capacitor being to prevent spectacular fireworks if this throw-out antenna happened to touch something earthed and the power-connector was phased so the chassis happened to be live.

[turretslug]

I imagine it's from the back (under the cover) of a US-made set (hence "tubes" and antenna"), two windings comprise a tuned winding and an external coupling aerial winding with its screw connection. "Remove screws to replace tubes" means it's in the way for "toob" replacement and normally attatched to metallic bracket(s), by which the capacitor is connected to chassis. This capacitor might be to isolate the main winding to DC for AGC purposes, or to isolate the coupling winding with an "AC/DC" power supply (though, in the latter case, connecting the cap directly to the "antenna" terminal would make more sense, as it would avoid stressing the inter-winding insulation).

Just my suppositions, anyway.

An aerial something like this was very common for MW table set use, the US didn't use LW like us.

[SurreyNick]

I think I see. The tuned winding you refer to, is that similar or the same as an aerial tuning coil as seen in a TRF or Regenerative receiver? If not, can you explain what function it performs?

Thanks

Nick

[Herald1360]

Yes, the tuned winding is the front end tuned aerial coil (or more generally, inductor). There won't be another one on the chassis. It could as well be used on a TRF as on the more common AA5 superhets where it would normally be found.

I had an Admiral set as a lad with exactly that kind of loop antenna inside the back of the set.

See here for a typical installation:

http://www.radiomuseum.org/r/admiral...ch_5n15_n.html

[SurreyNick]

Excellent! I get it.
Out of interest, would the set have worked well just relying on the external coupling aerial winding i.e. without attaching the external 'throw-out' wire antenna?
Thanks
Nick

[turretslug]

They would- feeding straight into just a basic triode-hexode or the US-preferred self- oscillating heptode front end would bring in lots of MW stations, certainly enough for the average listener and ample source of fascination for those so inclined after dark (when distance reception opens up). They are strongly directional- which is both a plus and a minus. It was popular with battery portables for the windings to be incorporated in the lid and these sets were obviously more conveniently orientated than large table sets! I think that ferrite rod aerials came in in the mid-fifties and these rapidly superseded this type- I suspect that cost and manufacturer convenience counted here as much as anything.

A close comparison can be drawn with the directional loops used in radio compass (DF) receivers.

This type of aerial lives on in the much larger tuned loop still respected by MW DX fans.

[Tractorfan]

Hi,
It could be from a 'Zenith' radio, as mine has a very similar aerial which has to be removed to access the valves.
Cheers, Pete.

[jsbhavsar]

A 1968 Philips tube radio model 15RB487 in India that my Dad bought had a little different things then. The circuit chassis circuit contained heat-sink wires and all converged on to a self pressing clamp. A A4 size thin silver foil was installed at the inside base of the bakelite case and the clamp touched on the foil which acted as heat-sink. A similar clamp was present on inside top of the bakelite case with a small 4 x 4 inch silver foil there. That thin silver foil on top acted as a "internal SW antenna". A ferrite rod antenna was also there. However, the radio did not sound effective on SW with only the silver foil antenna. It sounded well only on a long wire antenna.

My grandfather bought a small transistor radio in 1985 after his 1969 Bush Transistor died down. It was tiny and could be carried anywhere, worked on two C size batteries. What they did then, inside the radio they wound a thin insulated copper wire several turns inside the plastic body. That acted as the MW antenna or 'tuned antenna' because the radio anyway also had the whip antenna for SW.