Aerials for old domestic valve sets.

[crackle]

Here is a link to the KB Rejectostat aerial system. http://www.kbmuseum.org.uk/kb_servic...ctostat_kb.pdf
Many of the KB receivers in the mid 30's were equipped to be used with the "Rejectostat Aerial" as well as a normal long wire and earth.
Mike

[Mike. Watterson]

1) The vertical is too short to be much use on MW and esp. LW.
2) An open ended wire picks up E Field interference FAR better than Radio waves (EM), especially as the wire approaches 1/10th wave or less. Any typical wire is MUCH shorter for MW.
3) Medium distance variable fading (higher SW bands during day, MW & lower SW after dark) is purely an ionospheric effect and rare on MW anyway, not much to do with aerials.
4) Only open twin feeds used in last 50 years and for matched aerials, only coax is used as an ordinary aerial feed, with suitable matching.

All this is in ARRL, RSGB and Communications engineering textbooks. The quoted book is only a source for SERVICE technician information, repairing radio and TVs, not design of radio, TV, aerials or installation of aerials. It's got a lot of outdated mythic information. Hardly updated since 1954 (my edition). It wasn't ever a professional Engineer's text only for Service Technicians. Yes, I know in the English speaking world it's common to call the guy that plugs in a set box or repairs a TV, an Engineer. They used to be trained qualified technicians. The home visit person from Sky or Virgin is now barely more than a delivery person and may have had only a week's training, not the C&G or HNC or whatever in the old days. Really "The Radio and Television Engineers Reference Book" is a 1950s text for qualified Service Technicians. It mentions various subjects in a very untechnical inaccurate way. It's got a little bit of everything, a sort of encyclopedia for people repairing things.

TV and VHF radio is 100x to 1000x the frequency of MW & LW. The horizontal and Vertical polarisation is well defined, especially TV and the Ionosphere is never involved. VHF Radio (Band II or Band III DAB) mostly now is slant or circular polarised, which gives 1/2 the receive power but means the polarisation change of a reflection or angle of a whip does not matter.

At any distance from the transmitter on LW, MW and SW the polarisation isn't well defined. Also the aerial wires are TOO SHORT to be properly H or V polarised.

I've also worked with 10.5GHz Line of Sight two way systems for broadband to the home. The H and V is so well defined and wavelength so short that the aerial panel as 32 horizontal dipoles on one half and 32 vertical on the other and the system transmits and receives only 4% apart in frequency using opposing polarisation.

That's not possible on UHF, worse on VHF and forget about polarisation discrimination on MW, never mind LW unless you have a 75m high vertical or a 150m wide FOLDED dipole!

[crackle]

When in my car I know that with my not so local "Gold" transmitter on 1548khz at nearly 10kW, after dusk there is a very rapid fading (pulsing) effect, sometimes along with foreign interference. It seems like the overall volume of the received signal drops significantly.
The Gold TX antenna is directional and we seem to be in a bit of a blackspot here in In the SE of Essex.
On the other hand R. Caroline on the Suffolk coast using the old BBC World service standby antenna at only 1kW is very strong all around my area, it is almost twice the distance from me as the "Gold" TX.

Mike

[ms660]

I used to get fading on UK MW transmissions at night time down here, the distances quoted in the book seem to tally up with some graphs I've been looking at, as regards the properties of a vertical antenna the book is correct so far as I can make out.

Lawrence.

[Mike. Watterson]

Only at much higher frequencies or an enormously big vertical.
Also as you get further from the transmitter there is more of a variation of polarisation.
Of course there can be MW fading, it's due to ionospheric propagation and a vertical won't solve it. Actually can be really bad driving as you hit peaks and nulls of the ground wave and skywave interference / phase changing. A vertical doesn't help with polarisation unless it's much longer than 1/10th wave. The 1/4 wave and 5/8ths wave are good, but not practical for MW.

[John Wakefield]

As others have said, back in the day you just ran a length of wire (old field telephone cable) from the aerial socket down the garden to a suitable pole, usually a clothes post or tree. At the pole end the wire was terminated with a porcelain insulator before another piece of wire attaching it to the pole. The longer the wire the better the reception, particularly with weak MW stations like Radio Luxenburg.
The earth socket was just a wire to a convenient water pipe or outside to a copper rod into the earth.
Of course those days many houses had long gardens so not a problem, these days with no gardens it may be a problem arranging a suitable aerial. Some sets had a frame aerial within the back panel. Just a coil of wire running around the circumference of the panel. In practice these did not work as well as the outside aerial unless you were near a transmitter and had a good signal.

[DoubleWound]

Almost exactly my memories but I'm not sure that too many folks bothered about the earth.

My recent tests on several old valve radios showed that no earth, mains earth or a ground spike earth made no difference to reception or interference at all.

Please discuss.

[crackle]

I agree, with a good long wire aerial an earth makes very little difference on MW. It maybe down to the strength of the signals, as you tend to not pick up distance signals as much on MW.
But on SW my earth does make a noticeable difference.

Mike

[Mike. Watterson]

Crystal* set or a battery set with a long aerial the earth makes a HUGE difference. It won't on most mains sets, or sometimes it increases the interference, especially here as here the standard is to bond neutral and earth at the meter unit and have an earth rod connected to that. So inherently it's hard to see how an actual extra earth connection will make any difference to a mains set. If it's got an internal aerial and two core flex it increases interference slightly on MW & LW.

I found I had to add a 1kV 1nF capacitor from isolated shaver transformer secondary centre tap to mains earth to reduce interference on battery valve sets run off that transformer on 230V or 115V. Makes no difference to signal.

Lowest interference is a battery set (valve or transistor, frame aerial or ferrite rod) running on batteries.

I ONLY get distance signals on MW!

Ewan Fane was here from Cork today and we tried various sets on LW BBC R4 (which is pretty far from Limerick).

(* 1N60 diode, 10K resistor, ceramic disc earphone and coil wound on PET drinks bottle, ordinary transistor radio polycon with both parts shorted, shunt capacitor for LW)

[Synchrodyne]

This is a most interesting debate. Against the possibility that was written in Section 21 of the Radio and Television Engineers’ Reference Book (R&TVRB) is inaccurate, I read through Sturley’s (*) long chapter (63 pages) on “Aerials and Aerial Coupling Circuits”, which provided a detailed mathematical treatment. With the caveat that this is as seen through a layman’s eye, not that of a professional electronic engineer, I cannot find any material disagreement between that and the much more condensed treatment provided in R&TVRB. And Sturley I think is regarded as an authoritative source.

Here is a short quotation from Sturley about the various kinds of open aerials used for LW/MW/SW reception:

“The open aerial can itself be further subdivided into the vertical, inverted L, the T, and the dipole aerial. The T and inverted L aerials are used principally for long and medium wave reception. They are less satisfactory (especially if they are long) for short wave reception, because the aerial becomes a resonant circuit when its length is approximately one-quarter of the wavelength of the desired transmission. This has a serious mistuning and damping effect on the first tuned circuit unless coupling is very loose. The dipole aerial, consisting of two symmetrical open aerials connected to the receiver by a feeder, is mainly employed for short wave operation, and its particular advantages are that it has directional pick-up and can be conveniently connected to the receiver by a balanced feeder, so reducing interference pick-up. For long and medium wave operation the inverted L aerial having a long horizontal top and vertical lead-in has been extensively used. Its horizontal top enables the voltage picked up in the vertical limb to be used more efficiently, and the equivalent open circuit voltage generated in a given length of vertical is increased by the addition of a horizontal top. It has, however, the disadvantage of collecting vertically and horizontally polarized components of a transmitted wave. These components, having a random phase relationship, tend to cause fading and distortion. The vertical aerial is slowly superseding the inverted L aerial because it responds only to vertically polarized transmission, thus minimizing fading and distortion due to obliquely, circularly or elliptically polarized transmission. It is also simpler to construct and erect.”

Sturley also covered anti-interference/antistatic type aerials, with the summary comment these could provide a 30 to 40 dB reduction in interference at the cost of a 3 to 6 dB reduction in wanted signal level.

Regarding the nature of R&TVRB, a look through the provided short biographies of the many section authors shows quite a few who were involved in research and development and product design, and many of the chapters appear to have been written as much from that viewpoint as from the servicing and maintenance side. For example, Section 16 “Commercial High Frequency Radio Links” and section 22 “Communications Receivers” were both written by F.W.J. Sainsbury of Marconi, who judging from other articles by him, was a major player in the development of the Marconi point-to-point receivers, such as the HR92, in the 1950s. For section 14 “Broadcasting Receivers”, the first part on valved receivers was written by L. Driscoll of Murphy, who appears to have been the designer of such models as the TA160, regarded as one of the top export models of its time. The part of section 21 on AM receiving aerials was written by P. Jones, then the head designer at Aerialite. So I should be circumspect in invoking “false authority syndrome” for this book or part thereof. Any thoroughgoing rebuttal of what was written in respect of AM aerials would I think need to “undo” Sturley’s mathematical analysis and synthesis to be fully credible.

With AM aerials, the results obtained tend to be situation-specific, and what works well at one site might not work at another. In one case, many decades ago, I found that a 6-metre vertical whip worked better than a long wire that was probably around 25 metres in length. Looking back, I suspect that this was because in that case, the top of the vertical was a lot higher than that of the long wire. As to earthing, whether or not a dedicated earth connection is beneficial depends upon whether it materially improves upon whatever other earth “connection” is available. With an open aerial connected to the top end of the receiver input coil, the bottom ends need to “connect” to earth somehow. Where the receiver is of the class 0 or class II type, then absent a dedicated earth connection, earthing will be via capacitive coupling (natural capacitance) to whatever is nearby and conductive and is eventually connected to earth, such as the power supply neutral conductor. With a class I receiver, earthing it is likely to be via the power supply protective earthing conductor. The efficacy of these is likely to vary site-by-site. Here in NZ, our MEN distribution system means that there is a very local earth – usually a spike - for each consumer, and the neutral is bonded to this earth at the switchbox. So in some cases the protective earth will be adequate as an RF earth, and so might be capacitive coupling to the neutral.

Re the details of anti-interference aerials, Sturley indicated that the feeder-to-receiver transformers were designed on the basis of a receiver input impedance of 2000 to 3000 ohms. Nothing was said about feeder characteristic impedance, but I think that the screened twin typically used would have been around 75 ohms. Support for that comes from the fact that Belling & Lee noted in its advertising that its screened twin intended for antistatic aerial applications was also suitable for use as a TV aerial feeder. At the time it was advocating the use of 75-ohm balanced twin as well as 75-ohm coax for use with TV aerials.

Anti-interference aerial systems seem to have been offered by most of the major UK aerial manufacturers in the post-WWII period. Usually these were available for use with long wire systems as well as with verticals. Aerialite at least continued to offer such through the 1970s. In the late 1940s/early 1950s, combination TV and AM aerials were also offered, in which the TV mast assembly acted as the vertical AM receptor. These appeared to have separate TV and AM feeders. Another much later variation, offered at one time by Hirschmann and probably others, was a combination FM-AM aerial system with the AM vertical mounted atop the FM Yagi and connected into the coaxial feeder via a suitable transformer (and presumably a frequency dividing network), with another unit at the bottom end to separate the FM and AM signals and match the AM signal to typical receiver input impedance (maybe 1 k or so in the solid-state era). It seems to me that one possible advantage of an AM aerial that reaches the receiver by a two-conductor feeder, whether balanced twin or coaxial, is that the receiver is looking back into what appears to it to be a closed system. Thus the influence of whatever “earth” is coupled to the bottom end of the input coil is much reduced.

As Sturley said, aside from technical considerations, the vertical aerial had the advantage of easy installation. Getting the top of the aerial say 15 metres or so above ground would not have been difficult in many domestic situations. Also, for use by the general public, the aerial manufacturers need to offer “fit- and-forget” products that did not need to be re-oriented, retuned, band-switched, etc, for different stations.

I suspect that what has changed between then and now, as it were, is not basic aerial theory, but the spread of the interference field. At one time, getting the base of vertical aerial several metres above the highest point of a house would have been sufficient to take it outside of the worst of the interfering field generated by household equipment. Less so these days, though.

Originally Posted by Mike. Watterson

Only for local signals, and even then not always. Masts can be horizontal wires (common for LW) or vertical like Lisnagarvey N.I. Sites often have both.

My understanding is that LW and MW ground waves are vertically polarized regardless of the type of radiator used. (I am not even sure that one could have a horizontally polarized ground wave.). Where L or T radiators are used, the horizontal part simply acts as a “capacity top”, and lowers the radiation angle of the emission from the vertical part. Primary service areas are defined by the ground wave reach. The skywave can have its polarization altered when traversing the ionosphere. When skywaves have nuisance value only, then some polarization selectivity in the receiving aerial could be of advantage.


(*) K.R. Sturley; Radio Receiver Design, Part I, Radio Frequency Amplification and Detection; Chapman & Hall, 1943.

See Chapter 3, Aerials and Aerial Coupling Circuits, p.57ff.

It is available on-line at more than one site, for example see: http://www.keith-snook.info/Stuff-yo...%20Sturley.pdf


Cheers,

[Mike. Watterson]

An electrically short aerial is not a vertical or horizontal aerial within the meaning. That is what is not pointed out in the original text.

I've consistently pointed out that on MW you'd need at least a 20m long vertical for what the book says to apply, and 75m long to be comparable to a 1/4 wave whip on VHF. The vertical was originally called a Marconi Monopole.

So without proper explanation of dimensions the original text is misleading. The fact is that physically, mathematically (and practically today) an electrically short vertical simply picks up interference more than anything else on MW. Even a 9m (30ft) vertical is only 1/40th of a wavelength on 350m (about the middle of the band). That's one TENTH of the ideal size for a MW vertical. You can match it better with a capacity hat (long wire to top) and a series coil at the base, however it's not going to pickup less local E Field and improve the Signal to Noise.
A vertical of a practical size is possible on SW. If the vertical is electrically long enough the text is more accurate.

If there is local electrical interference, then only a ferrite rod, loop or screened loop works well for MW and LW. Especially if the radio is earthed. Connect a mains earth to your car in the driveway near the door and try MW & LW on it with CFL lamps, chargers, TV etc running. Compare then with any decent battery set (transistor or valves, frame loop or ferrite).

[John Wakefield]

From what I recall from the 1950's the earth connection did not really have any effect on the reception but may have reduced mains hum. I think it was more of a safety feature as at the time many houses had limited 3 pin 5amp or 10amp wall sockets & people used to plug radios into lighting sockets which of course did not have an earth return.
I also recall that in some houses there was a circuit breaker where the aerial wire come through into the house. Presumably to disconnect the aerial in case of lightning

[Nuvistor]

Re the diagrams in post 24, figure 5d show the earth connection on the receiver. If this is a live chassis set the earth connection must be through a Y class capacitor.

The Belling-Lee Eliminoise system did have burnt out Eliminoise transformers due to radios having no or faulty isolation capacitors.
Information from WW. David who hosts the american radio history web site is rebuilding the server after major disc errors. Search facilities will be available after the rebuild if you want information on the Eliminoise system which appears to be very like the system in post 24.

[ms660]

As I said earlier, the vertical part of an inverted L is the most responsive to vertically polarized waves, MW and LW transmissions so far as I know are vertically polarized,

The first part of that was gotten from my copy of the R&TV Eng. Ref. Book and I believe that is correct in saying that, not only that book , W.N. Christiansen says the same in his section of RDH4 (Radiotron Designers Handbook 4th Edition) on antennas, I think Terman does too in his Radio Engineering book.

The latter two books are well respected for sure and the first book (R&TV Eng.) is one I've always relied on when I was in the trade and ever since.

Also to be clear, the vertical antenna described in R&TV Eng. does say that the top of it would be 50ft above ground level, which for most would be considered as a height that would provide a very good signal strength.

Lawrence.

[Hybrid tellies]

Gordon J King wrote an excellent book on TV and Radio aerials. Mostly aimed at TV, VHF and UHF, and FM aerials but I am sure there was a chapter on AM aerials. I will take a closer look at this over the weekend.

When I lived in west Cornwall reception of Radio 1 on 247m and Radio 3 on 464m was very poor only the better full superhet radios would pull them in during the day. At night both these stations would be swamped out by continental interference. My old valved HMV 1124 worked really well with about 60' of lighting flex wrapped around my bedroom and the earth connected to the mains earth. Everyone was amazed at how well this worked on all the AM bands.

Thanks to the ridiculously high levels of noise and interference emitted by most modern electronics and carried on the main wiring, including the mains earth cable, the best policy is to put as much distance between your radio and the mains wiring.

I run all my AM transistor radios on their internal batteries and use the directional properties of the ferrite rod aerial to maximum effect to get the clearest reception. Sadly thanks to the very high levels of local noise from surrounding houses, some of which have aging Plasma TV's, it is now impossible to run any of my mains valved radios on AM. The weaker signals are swamped by the high noise levels and the stronger signals all have an unpleasant hum and buzzing noise in the background which is modulation hum induced from the main wiring.

I have a general coverage communication receiver covering from 30Khz to 30Mhz. It use to run well on a few meters of open wire strung high in the loft with a mains earth now its totally useless just picking up noise and interference. As its a reasonable quality communications radio if you disconnect the aerial you cannot hear anything including the very strong signal we use to get from the nearby local transmitter. Just for a test I ran this radio up with no aerial and was amazed at the noise and interference that I can now hear especially across the higher end of the medium wave band.
It might be a good and interesting test for everybody who has the same problem with noise and interference on valved radios without an internal aerial to see how much or how little interference there radios are picking up from the mains. Of coarse if your interference proves to be coming in from the mains supply you may well have to try using a mains input filter using mains rated X or Y capacitors. Only do this if you feel happy and safe working with mains supply.

Simon

[Mr 1936]

Let's take an imaginary journey back to the 1940's and 50's. Not much electronics around then to generate interference, but plenty of electric motors, switches and thermostats which may or may not have been fitted with suppression components. House wiring much like today. This was the world the Rejectostat, Skyrod and Eliminoise were invented for. As far as I can see, the rod effectively forms the top of an asymmetric vertical short dipole, with the screened lead acting in common-mode as the lower "leg" which was then grounded at its base. The effective feedpoint would be at the base of the rod. Now, I have no way of telling how successful they were at rejecting household interference versus a conventional longwire plus downlead, but I suspect they must have shown some genuine benefit, i.e. not all marketing puff. The explanation in R&TVRB seems reasonable to me, and I wouldn't rush to criticize it.

Fast forward to today. Within the service area for MW and LW (Forget Luxembourg) we are talking groundwave with almost pure vertical polarisation. So way out in the countryside an electrically short vertical rod or an electrically small balanced vertical loop/horizontal ferrite will work equally well.

As we travel nearer to built-up areas we have to contend with rising levels of vertically polarised groundwave propagated interference from thousands of sources. Our rod or loop will BOTH suffer this interference, though the two directional nulls of the loop might help IF we are lucky enough to have the interference from predominanly one direction and the wanted signal from another.

Finally, coming to within very roughly a quarter wavelength of our interferer filled house we will often find the loop a better bet, as for nearfield interference the E field often dominates - but only experiment will tell. Increasing the distance between the aerial and this very localised interference will help of course, provided any feeder cable is arranged to not pick up any signal.

Worth noting that putting a gapped screen around a loop is merely a technique to improve its balance, i.e. reduce incidental unwanted pickup of the E-field.

I am not aware of any longwave transmitting aerials which use horizontal conductors as anything other than a "capacity hat" to improve efficiency. Vertical polarization is radiated exclusively.

[crackle]

I would think that horizontal polarisation was more the norm back in the 30's and 40's. When KB were marketing their Rejectostat, their drawings and recommendations all showed a long horizontal wire with a down lead.

Interference back then could possibly have been as bad as now, especially in the towns. With neon signs, unsuppressed car ignition, electric motors. Were the currents being switched likely to be higher than today's small switch mode devices.

Mike

[ms660]

Originally Posted by crackle

I would think that horizontal polarisation was more the norm back in the 30's and 40's. When KB were marketing their Rejectostat, their drawings and recommendations all showed horizontal wire with a down lead.
Mike

Vertically polarized for MW and LW, horizontal wouldn't work well at all, the E field would get shorted out by earth.

The manual for the Rejectostat in effect says that some of the signal is lost due to the reduced length of the vertical down wire that would normally be there.

Lawrence.

[G8HQP Dave]

Originally Posted by Mike. Watterson

1) The vertical is too short to be much use on MW and esp. LW.

No. Signal strengths are high so the short antenna is fine. Sadly, noise levels are high too - that is the reason why a vertical might not work too well. Being short is not a problem.

2) An open ended wire picks up E Field interference FAR better than Radio waves (EM), especially as the wire approaches 1/10th wave or less.

True that a single wire picks up local E field interference quite well. I am not sure that this gets worse as the wire gets shorter.

Originally Posted by Mike. Watterson

A vertical doesn't help with polarisation unless it's much longer than 1/10th wave.

Not sure what this means. A vertical responds to vertical polarisation whatever its length.

Originally Posted by DoubleWound

My recent tests on several old valve radios showed that no earth, mains earth or a ground spike earth made no difference to reception or interference at all.

Probably two things going on here:
1. as the aerial input on a domestic set is high impedance a bit of stray capacitance can provide an 'earth'
2. signal strengths are high, as is noise, so in many cases improving the antenna system may just boost both by a similar amount

Originally Posted by Mike. Watterson

An electrically short aerial is not a vertical or horizontal aerial within the meaning.

Not sure what you mean by this. A short antenna - even an infinitesimally small antenna such as an elemental electric dipole - still has an orientation. Whose "meaning"?

That's one TENTH of the ideal size for a MW vertical.

But we don't need an ideal size for picking up high power broadcasts. I don't know why you persist on wanting long antennas for local broadcast. An infinitesimal dipole has gain less than 1dB below a halfwave dipole, so the only issue is impedance matching and that does not matter too much with such strong signals.

Having said all that, I suspect that the elevated monopoles worked partly by having incomplete common-mode isolation so the feeder was part of the antenna. This is a common feature of small antennas, especially any with 'magic' properties.

Local noise is partly vertical E field and partly longitudinal E field. A monopole picks up both quite well. A dipole is better, as it can balance away the longitudinal part - that may be why dipoles are reported to be quieter than verticals, irrespective of orientation. A loop will not respond to longitudinal E field, especially if screened. A good alternative may be a short active dipole, ideally mounted away from buildings.

[ms660]

Here's good primer on antennas and propagation, after reading the page click on "next page":

http://www.tpub.com/neets/book10/42.htm

Lawrence.