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Old 9th Jul 2019, 9:44 pm   #1
LyntonP
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Default Aerials for old domestic valve sets.

Several of the old valve sets that I own have only a single connection for the aerial plus a connection for an earth.
Suppose you already have a sizeable dipole aerial do you
1, connect both sides of the dipole together to the aerial terminal and connect an earth to the other terminal?
2, keep both sides of the dipole separate connecting one to the aerial socket and the other to the earth terminal?
Which would be best?
Lynton
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Old 9th Jul 2019, 9:59 pm   #2
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Default Re: Aerial for old valve sets.

Hi Lynton, the answer is 2. However, the length of the dipole will determine how good an aerial it is and it will work better on some frequencies than others! If you use option 1 you are doing no better (and possibly worse) than a simple long-wire. A long-wire wound around your loft may be the simplest solution if feasible for you. Cheers, Jerry
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Old 9th Jul 2019, 10:22 pm   #3
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Default Re: Aerial for old valve sets.

Quote:
Hi Lynton, the answer is 2. However, the length of the dipole will determine how good an aerial it is
Hi Jerry
The aerial I have is a G5RV which is a 102 ft dipole (plus the 300 ohm ribbon feeder). I erected it for use on the HF bands and it fed my shack in the loft. It has since been extended down into the shed for short wave broadcast listening. At its highest point it is just higher than the chimney pot but it did work very well on the amateur bands.
I am working on getting a feed into the lounge so I can use it with any set I have in there (only one at a time allowed)!
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Old 9th Jul 2019, 10:47 pm   #4
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Default Re: Aerial for old valve sets.

Well, theoretically, the dipole - if fed with coaxial feeder - should be connected to a receiver with a 50 ohm input impedance, since a dipole at usual heights above ground will have a Z of about 50 ohms impedance at its resonant frequency.

In reality the two sockets of a vintage radio will not have 50 ohms impedance between them. It will be all over the place depending upon frequency. The dipole will also have a widely varying frequency outside its resonance.

The inputs on old domestic radios were originally designed for a random length of wire and an external separate earth - often a water pipe or earth stake just outside the house.

In practice it probably won't matter how you connect it up. But I'd be minded to strap both sides of the dipole together and connect it to the antenna input, and connect an earth. Mains earth probably best avoided so use a decent separate earth. That way the whole antenna acts as one 'receiving bit of wire'. It'll still have an widely varying Z, but no more than a random wire.

The problem with a dipole/G5RV is that the coax connecting it to a wildly varying input Z acts as a capacitor and some frequencies will be in effect short the signals to earth.

Just try that. Connect the coax outer to the receiver earth as you tune around and you'll see what I mean. Sometimes signals are stronger, sometimes weaker and sometimes just more noise.

Play around and see what works best, although I doubt you'll listen much on short wave - if your vintage radios cover that. The G5RV will be way off resonance on LW/MW anyway so may be a bit noisy picking up all sorts from the outer of the coax.
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Old 10th Jul 2019, 12:49 am   #5
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Default Re: Aerial for old valve sets.

A loop aerial, about 40cm dia or more, is best for MW. Try about 20 turns. Switch in about 2.5mH in series for LW.
Dipoles are only good on higher SW bands and VHF-FM. Also the input impedance of the aerial socket on AM sets is quite high, designed either for a loop or 2m to 15m wire. A wire will pickup far more interference.
The French in the 1930s often used loop aerials fitted to the rear of prints or paintings. Some had a tuning capacitor. I've found some sets are best without the tuning capacitor and others benefit.

So forget a dipole, except maybe on 20meters (15MHz) or higher, even then you'd need a matching transformer.
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Old 10th Jul 2019, 9:06 am   #6
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Default Re: Aerial for old valve sets.

Hi Lynton P. The answer to your question is - it depends ! The G5RV is a balanced horizontal dipole which gives a reasonable match to roughly 50-75 ohms for transmitting on the 14 MHz (20 metre) HF amateur band. On other bands the impedance will generally be higher, so a tuned matching device is used to transform it.
If you want to listen to skywave HF, either connect the twin feeder to the Aerial and Earth terminals or better still interpose a balanced to unbalanced transformer which will help reject local interference pickup on the feeder. The antenna will pick up the horizontally polarised component of the incoming mixed polarized signal. Impedance mismatch isn't usually a problem for reception, as the HF external noise level from worldwide sources is so high it will often comfortably override internal receiver noise even with an inefficient antenna or inefficiently matched antenna.
If your interest is Long and Medium wave reception, the signal will be predominantly Vertically polarized groundwave. In this situation, connect both legs of the feeder to the Aerial socket and a proper RF earth to the Earth terminal. The feeder will then act as a vertical monopole, with the dipole arms as a "capacity hat" which will increase its signal pickup by up to 2 times. Again, impedance matching will not be important as you will have more than enough external noise pickup to override any receiver noise.
The idea of tuned matching for a receive-only antenna only really applies if the receiver is particularly insensitive (crystal set, pre-1930's era etc) or if the antenna is extremely small in wavelengths. Otherwise, the typical effect of tuning is to increase the signal and the external noise by the same amount, which leaves the signal to noise ratio unchanged.
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Old 10th Jul 2019, 10:08 am   #7
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Default Re: Aerial for old valve sets.

In my younger days back in the 1970's I was running my HMV 1124 valved radio with a large 60' long wire aerial going the length of the garden plus a good earth which gave good results across all of the AM bands.

Just for an experiment I made a half wave dipole, made of lighting flex and a short coax feeder from the centre of the dipole to the radio, with the centre feed going to the aerial socket and the screen going to the earth socket. It ran the entire length of my large bedroom running from the front bedroom window to the back bedroom window so I suppose it was probably about 9-10m long running north-south.

Reception on anything below 12Mhz or from Long Wave down to the 25m short wave band was terrible with reception improving as you tuned up through the 19m and 16m bands. The natural peak for a dipole of this length would have made it ideal for the 11m or 26Mhz broadcast band.
For this reason and calls from the rest of the household to take this unsightly hazardous thing down before they ripped it down. Well I did share the room with brother who on several occasions nearly strangled himself on it lol.

To make an effective half wave dipole for Long Wave the total length would need to be 750m for BBC R4, and for Medium wave 250m for the low frequency end and 100m for the high frequency end.

I would stick to a wire aerial and earth or use a loop aerial both of which are more effective and compact aerials for Long and Medium wave reception.
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Old 10th Jul 2019, 10:37 am   #8
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Default Re: Aerial for old valve sets.

You will probably get the best results overall if you connect both wires of the feeder to the aerial socket and connect the earth socket to a central heating radiator. You are then using the dipole and feeder as an untuned long wire. As was said earlier, domestic valve radios were intended to be used with a random length of wire strung out across a garden or back yard.
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Old 10th Jul 2019, 11:32 am   #9
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Default Re: Aerial for old valve sets.

Three different answers from the first three replies!

A dipole would be good, but as Simon Hybrid Tellies points out, it would be big for MW and even bigger for LW. Even the Droitwich transmitter aerial is only 180m long, so much less than a half-wave dipole. So, forget this as impractical!

That being so, if you have a dipole (maybe for SW or FM), for MW and LW just connect the pair together and to the aerial terminal, and connect an earth to the earth terminal (though often this can be dispensed with). An earth from an earth rod is best, though some electrical installations may fall foul of regulations if you do this. Paul Sherwin's advice is good.

A loop aerial should work well and be relatively interference-free (except for very close sources of RFI). But output voltage will be low and it will probably need a matching transformer, which adds another variable!
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Old 10th Jul 2019, 12:31 pm   #10
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Default Re: Aerial for old valve sets.

On MW and LW you will probably get stronger signals, but more noise, by connecting both sides of the dipole to the aerial terminal. See which works best. On shortwave you may get better results by using it as a dipole, and should be able to reduce noise by adding a suitable balun.
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Old 10th Jul 2019, 2:25 pm   #11
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Default Re: Aerial for old valve sets.

Strapping the two 'legs' of the dipole-feeder together at the radio end and using the resultant "Tee" antenna connected to the radio's antenna-terminal in conjunction with a separate earth is one of the standard ways to use something like a G5RV or similar "HF" dipole on 160 Metres.

Given that the MW band is not that far off 160M I don't see why it shouldn't work.

Impedance-matching is likely to be less-than-optimal - most old MW/LW broadcast-radios with external antenna/earth terminals were generally reckoned to have an input impedance around 400 Ohms.

Try it and see! You've got nothing to lose.
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Old 10th Jul 2019, 6:26 pm   #12
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Default Re: Aerial for old valve sets.

As far as I am aware (and please correct me if I am wrong), if you connect _any_ aerial (at least a passive aerial) to a valve radio you will do no damage to the aerial or to the radio, and you won't cause serious interference to other radios (OK, I am aware of an exception to the last part but it won't apply with this sort of radio).

In other words, try it with both wires on the aerial socket (as a 'T'), try it with one on the aerial, the other on the earth socket, etc. Whatever works best is the one to use.
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Old 10th Jul 2019, 7:52 pm   #13
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Default Re: Aerial for old valve sets.

If you don't mind the extra tuning, you could always try a tuned loop aerial.

There's been several discussed in here, but here's a sample:

https://www.vintage-radio.net/forum/....php?p=1016777
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Old 10th Jul 2019, 8:42 pm   #14
Mike. Watterson
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Default Re: Aerial for old valve sets.

Though some sets work better with an untuned loop. Even bell wire or Cat5 cable wound round a cardboard box can work better than a long wire due to ability to null an unwanted source and lower E field pickup (less local interference). No need to strip Cat 5 apart, just tie all the cores at both ends.
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Old 10th Jul 2019, 9:16 pm   #15
Ian - G4JQT
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Default Re: Aerial for old valve sets.

To be honest, I used an Ekco A23 for years with just a wire loop around the ceiling. One end in the antenna socket and one in the earth soket. Signals were slightly weaker than a random wire down the garden, but noise was significantly reduced.

That's not how the antenna input circuits were aligned for, but it worked for me.

This thread has some complex content. If you're using a communications receiver, antenna types/matching/impedance is important. But for general coverage listening on a domestic set just sticking something in the antenna socket and adding a decent earth is all that's required.

Don't get bogged down in all the technical details.
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Old 12th Jul 2019, 6:43 pm   #16
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Default Re: Aerial for old valve sets.

Very interesting comments with quite diverse answers. Up to now the 5RV has performed by far the best in my case mainly due to the fact that it is the highest and longest I have tried to date.
Over the past few days I have constructed a 40 inch magnetic loop, and a very quick trial this afternoon gave some interesting results. It is very directional and it has been possible to reduce interference to zero when tuned to any station. It has also found stations I previously could not hear- not very loud but just about readable, no doubt more stations will appear after dark. The tuning capacitor had less effect than I expected but did function. Even connecting both gangs of the capacitor in parallel didn’t make too much difference. I only did a quick trial with the aerial indoors but the chances of it staying on the dining table are very slim!
It is not really a practical aerial for me due to its size and the fact that you have to have both the radio and aerial in close proximity.
If I can cajole a neighbour of mine to climb my ladder and put some fixings up on the fascia then a Radom length wire up in clear air may be next.
I understand that aerials are an extremely complex subject and I don’t want to get bogged down in all the theoretical discussion (not that I understand it anyway) but the old adage that any aerial erected in the clear as high as possible will be a ‘good’ aerial.
Thanks for all the input. Very interesting reading.
Lynton
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Old 16th Jul 2019, 3:07 pm   #17
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Default Re: Aerial for old valve sets.

Quote:
Originally Posted by paulsherwin View Post
You will probably get the best results overall if you connect both wires of the feeder to the aerial socket and connect the earth socket to a central heating radiator. You are then using the dipole and feeder as an untuned long wire. As was said earlier, domestic valve radios were intended to be used with a random length of wire strung out across a garden or back yard.
If you connect the earth socket to a central heating radiator you are almost certainly connecting to mains earth and so just fit a three core mains cable if the set is not AC/DC. BTW, I dislike AC/DC sets with an isolation capacitor in series with the chassis and earth socket.

Regarding coax feeders from a dipole I've tried everything mentioned for LW/MW and the results are no better than a few metres of plain wire.

I am often advised by an expert that a loop aerial is the way to go.
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Old 16th Jul 2019, 3:45 pm   #18
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Default Re: Aerial for old valve sets.

My own theoretical knowledge could be written on a stamp, but one illumination I received is that the downward connecting wire from a long wire is significant. The higher the aerial, the longer this is. But the aerial needs to be close to the set, the down wire vertical. I have such an aerial in my garden, and it is great in the shed, but inconvenient in the house as the garden is at the back, and my radio room upstairs at the front - so I am also looking into tuned loops.
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Old 16th Jul 2019, 4:05 pm   #19
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Default Re: Aerial for old valve sets.

My knowledge on aerial theory is also weak but I know what works and doesn't. I had excellent results very many years ago with a long external garden wire aerial but there's so much interference these days such an aerial is not so good anymore.

I will have to get around to loop aerials soon.

Ref my previous comment on central heating radiators, most new houses will be plumbed in with plastic pipe and so that's another point to bear in mind.
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Old 17th Jul 2019, 7:48 am   #20
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Default Re: Aerial for old valve sets.

I suffered terrible interference from time to time on my original long wire aerial. It was one I had simply strung from an air brick on the house to a tree in the garden, and was about 10m long.
I erected a new one, this time higher and longer, to a 20 foot mast I made from some 4x2 and an old wooden dinghy mast. The length of the new aerial horizontal is about 17m and the down lead is about 5m.
This time I used the root of the chimney as the anchor point on the house.
I threw a ball over the roof with a 50lb fishing line attached, then threw it back over again, this time round the other side of the chimney.
The fishing line was used to pull a decent sized rope around the chimney and this was used with an egg insulator to attach the aerial wire to, the rope is tied to a cleat fitted to the side of the house.
I get hardly any interference now.
The house wiring ring main forms a loop radiating interference all around the house, the whole of the aerial is now outside of this interference loop.
I dont know if the aerial will show up in this photo, but here is a photo of the house end of the aerial.

Mike
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Last edited by crackle; 17th Jul 2019 at 7:58 am.
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