Aerials for old domestic valve sets.

[ms660]

Originally Posted by Skywave

Well it isn't by me.

I no longer own that book, so cannot point to the many errors that I found in it.

Al.

Mine's the 4th edition, I still use it a lot, never had any problems with it to be honest, the section on receiving antennas seems ok to me.

Lawrence.

[Mike. Watterson]

To read, or actual wide variety of MW & LW aerials? It's more applicable advice to SW.

[ms660]

Originally Posted by Mike. Watterson

To read, or actual wide variety of MW & LW aerials? It's more applicable advice to SW.

It seems ok to me so far as the descriptions go, it's not a book solely dedicated to antennas, it's a general reference book, there's a section on Broadcast, SW and VHF/TV antennas.

In the days before Google I always relied on that book, the section on formula's etc was available as a separate book (Radio Engineering Formulae and Calculations, W.E. Pannett) which I utterly relied on as a reference for doing calculations which enabled me to pass the City & Guilds and UCLI exams I took, still got that little book somewhere.

I'm still of the opinion that it's a good book, there maybe some typo's etc but hey lots of "expert" books have also.

Lawrence.

[Station X]

Several posts moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=158302

[Synchrodyne]

Here are a couple of articles that may be pertinent to the topic.

The first is from Electronics Australia magazine, 1968 January.

Anti-Noise Aerial from EA 196801.pdf

It described an “anti-noise” AM aerial for home construction, based on a design from the (Australian) PMG’s department that had been extant for 40 years. One assumes that it was recommended by that department in situations where it was thought to resolve interference complaints, and presumably it must have worked well enough. (It seems unlikely that a department charged with resolving interference issues would recommend something that would not work very well.)

The aerial transformer had a turns ratio of 4:1. The receiver-end transformer was tapped to allow several turns ratios between 1:2 and 1:4, allowing optimum matching to individual receivers.

The aerial transformer was mounted close to the horizontal aerial span, with a vertical drop to earth from the other end of the primary. Presumably this would have been outside the interference field, and I’d guess that this vertical would be responsible for the major part of MW signal pick-up, whilst the horizontal acted as a capacity top. It seems to me that with a vertical for MW reception, the primary of the aerial transformer could be inserted almost anywhere along it with some results, although right at the bottom might be the best. On the other hand, for SW reception, the horizontal would be primary, and having the transformer right at the aerial would probably produce the best results.

The second article is from Wireless World 1952.

LW Loop Aerial from WW 195211.pdf

It described a loop aerial for LW reception, and compared its noise-reduction capabilities with wire aerials with both screened and unscreened feeders. It came out between the latter two.

The loop in question was tuned. Nothing was said about the effect that the Q of the loop might have on the receiver frequency response. For general entertainment a receiver bandwidth of around ±5 kHz would be appropriate, whilst for “quality” reception the number would be around ±10 kHz (which some LW transmitters, such as Allouis, but probably not Droitwich, could provide). My guess is that the loop Q would almost certainly compromise the latter, and perhaps also the former.

Also, in view of the comments made about the Radio & Television Engineers’ Reference Book, I have extracted that part of Section 21 that dealt with broadcast receiving aerials, LW, MW and SW. This is from the 3rd edition, 1960, but essentially the same content was used in the 1st (1954) and 4th (1963) editions, and by interpolation I’d guess also in the 2nd edition.

R&TVERB III part Section 21 AM Aerials.pdf

I should be interested to know where it is thought to have been significantly wrong, in a reasonably specific way, and not just in a sweeping generalization. In a descriptive sense, it does seem to have covered the practice of the day, in respect of both “DIY” and commercial products. And it did treat SW as a somewhat different case to LW and MW.

Clearly, a more recent (say 1990s) treatment of the same subject would need to be expanded to cover for example, but not only the ubiquitous ferrite rod, indoor loops (e.g. Palomar, McKay Dymek), outdoor loops (e.g. Liniplex and Wellbrook, although the latter might be later than the 1990s), very short active HF aerials (e.g. McKay Dymek whip and Datong dipole), and trapped dipoles for SW broadcast reception (e.g. Eavesdropper). The so-called “longwire balun” would also need attention and perhaps some debunking. On the one hand, it could be considered to be a reincarnation of the old anti-noise, screened feeder type aerial, with perhaps less attention to detail, in which case the balun was actually a unun. I think it was first introduced by RF Systems, who claimed that the descriptor balun was justified because the long wire was one arm of the dipole, with the coaxial screen serving as the other arm, and so the transformer coupled a dipole (balanced) to an unbalanced feeder. But if so, the coaxial screen arm of the dipole passed – as a signal collector - right through the interference field, pickup from which the use of the coaxial cable was supposed to avoid.


Cheers,

[ms660]

Thanks for posting the scans, I'm still of the understanding that the R&TV Eng. Ref. Book is ok, I've been using it for years.

Lawrence.

[G8HQP Dave]

Originally Posted by Synchrodyne

I should be interested to know where it is thought to have been significantly wrong, in a reasonably specific way, and not just in a sweeping generalization.

page 21-3: "Vertically polarised waves are reflected from the ground without change of phase".
Not true, but fortunately for vertical polarisation the geometry is such that change of phase is exactly what is needed.

Page 21-4: "It will be seen that the receiver is virtually connected to the centre of a short aerial in all vertical aerial-earth systems and therefore at a point of low impedance."
No, usually high impedance as the aerial is likely to be short. However, they may be confusing low radiation resistance and high reactive impedance, as both are characteristics of a short antenna. Hence the need to keep the earth wire at low resistance is not as pressing as they claim.

On the same page I note that they accept that the wire connecting to an elevated vertical rod is itself part of the antenna. In reality you can ditch the rod and just have a longer wire.

page 21-5: I am not going to copy out the paragraph beginnning "On medium and long waves".
Once again it confuses radiation resistance and total impedance. It seems to say that loss in the aerial conductors is what matters, and this can be reduced by raising the "characteristic impedance" (sic) by adding the horizontal top section. The truth is that the horizontal part acts as a capacitive hat. This increases the radiation resistance but decreases the capacitive reactance. As a result you get more signal, and delivered from a lower impedance so there is less loss in the potential divider formed by the antenna (series element) and receiver input (shunt element).

I am going to stop at that point. I suspect that this may turn out to be one of those technician-level books which gives good practical advice, backed up by false or confused explanations. They may tell you to do the right thing, but for the wrong reasons!

[Mike. Watterson]

Originally Posted by ms660

Thanks for posting the scans, I'm still of the understanding that the R&TV Eng. Ref. Book is ok, I've been using it for years.
Lawrence.

Most of it is fine. Some isn't.

[ms660]

Originally Posted by G8HQP Dave

On the same page I note that they accept that the wire connecting to an elevated vertical rod is itself part of the antenna. In reality you can ditch the rod and just have a longer wire.

Some folks interpret different to others....To me that seems like an Indian Rope Trick.

Lawrence.

[Mr 1936]

Thanks Synchrodyne for posting the pdf of R&TVERB. I have now read it several times, and was going to post the very few areas where I take issue with it, but G8HQP has beaten me to it ! With the exception of these, the text is 98% in accordance with what I understand from several decades study of antennas.

For anyone who wants to understand antennas deeply I thoroughly recommend looking at W8JI.com. He has spent many years studying, modelling and building all kinds of antennas, and manages to cut through some of the long established myths and misunderstandings that cling obstinately to the subject.

[G8HQP Dave]

Those who wish to understand antennas deeply need to read one or both of the textbooks by Balanis or Kraus. Some of the things which people argue about are covered there, and most of what people argue about can be dealt with by understanding those books even if the topic itself is not mentioned explicitly.

[Herald1360]

Originally Posted by ms660

Some folks interpret different to others....To me that seems like an Indian Rope Trick.

Lawrence.

You just need a skyhook.

Found in the same toolkit as snake oil, hen's teeth and rocking horse droppings, all of which feature in "wonder" aerial designs........

[Mike. Watterson]

I made a loop around an old clock with 3D scene under it:

1. Seven turns of STP Cat5 cable.
2. Short each of four pairs at both ends.
3. Connect resultant ends in series to create a 28 turn loop inside the 7 turn loop.
4. Radio was totally unusable on LW & MW with a 15m wire aerial at about 45 degree slope.
5. The composite loop is about 0.56 mH
6. LW: Put 2mH in series with aerial socket to loop and connect earthy end of screen on loop to earth connection. The noise/interference level is too high without earthing the screen. You can't earth at "live" end as that adds too much capacitance, reduces signal. You can't earth both ends as that would be 7 turn short. Near perfect R4LW and perfect RTE1 LW (unusable with wire).
7. MW: bypass the 2mH and disconnect the screen to reduce capacitance. Noise level is OK.
8. Connecting the wire aerial to chassis, or earthy end of loop or earth socket reduces the noise a lot on LW and quite a bit on MW.
9. For SW, use the wire aerial. The Loop on MW setting can be left in circuit or disconnected.

An unscreened open wire loop of 1920s / 1930 style with LW /MW switching picked up far too much noise on LW & MW and less signal on R4 LW. About 40cm and square, but points at top & bottom.

Next I'll try a pair of loops LW/MW at right angles in a card cylinder with a screen wire used as a SW loading coil / interference cancelling.
See 3rd photo:
https://www.radiomuseum.org/r/schnei...e_fm_1961.html
Likely I'll use some wood or plastic rods and square at top & bottom to wind the two coils and an outer shell of pizza box card to carry the spiral wire at right angles to the MW & LW coils that are at right angles. Bottom earthed and other end optionally SW whip.

I compared with a range of BIG ferrite rod aerials with LW & MW coils, varying from 1.7mH to 4.5mH for the LW, trying matching etc. All resulted in low interference pickup, but a fraction of the desired signal and more interference on LW than the screened loop.

I used 2 x 1mH "resistor body" style inductors in series (I had no 2.2mH or 2.7 or 3.3) as 4mH was too much. A high Q coil on the end of a ferrite rod peaked the loop on LW at about 2mH to 2.5mH, the cheap small inductors that look like 1/4W resistors were no worse. 1mH wasn't as good and 4.7mH was poorer.

Earthing even the earthy end of the Cat 5 cable screen on MW likely adds too much capacitance.

No doubt 20 to 30 turns of wire with a loose foil screen only earthed at one end would work better. However I've a giant box of UTP and STP Cat5 cable offcuts so I was curious.

Full dimensions and photos later. However you can experiment with any deep frame, taping wire to the inside rear and adjusting turns for best results on about 1.1MHz MW and then trying 1mH to 4mH in series for LW.
I have a photo frame in the library on a Pye 39 JH/E that uses heavy enamel wire like that, with a small slide switch to add the 2.2mH for LW. It works well on MW & LW and somewhat on SW on the MW setting. Adding a wire over the curtain rail works well for SW, and reduces interference if connected to radio earth on LW/MW. That loop aerial in a picture frame is about 6" (15cm) wide and 14" (35cm) tall, I think. No screen. It's on an upstairs windowsill so there is less interference.

[Synchrodyne]

Thanks much to G8HQP Dave for providing detailed comments on the R&TVERB section, and also to Mr 1936 for endorsing those comments.

Some more thoughts on the MW/LW vertical aerial.

Consider an arbitrary installation of a 5 metre rod mounted at the side of a house with its top being 15 metres high. The feeder drops vertically from it, with an earth rod directly below it, there being 10 metres between the bottom of the rod and the ground. Let’s say that the interference field from the house extends to a height of around 8 metres, and enough sideways from the house that the part of the feeder below the 8 metre level is within it.

The feeder is intercepted at some point by its connection to the receiver aerial and earth terminals, with the receiver input coil being across these. Let’s say that the receiver is against the outer wall of the house, so that only very short horizontal aerial and earth links are required.

First case, for a receiver on the lower floor, let’s say that the interception is at the 1 metre level. Thus the rod plus feeder then constitute a 14 metre vertical, with a 1 metre vertical earth wire.

Second case, the receiver is on the upper floor (if it is a two-level house) and let’s say it is at the 3 metre level. Then the rod plus feeder forms a 12 metre vertical with a 3 metre vertical earth wire.

The third case is that an antistatic system is used. Here the aerial transformer is fitted at the bottom of the rod, so at the 10 metre level. The transformer primary could be seen as being a proxy for the receiver input coil, allowing arbitrary remote location of the receiver at the end of a screened-twin feeder and receiver transformer. In this case the aerial is formed by the 5 metre rod, with a 10 metre vertical earth wire.

In all cases the vertical earth wire will act as an aerial and pickup both signal and interference. Presumably the higher it reaches the more it will pick up. I am not sure how the proportions would work out, but perhaps signal and interference pickup might increase at different rates as the earth wire got longer and higher. Also, given that the earth wire is (naturally) earthed at one end, although looking into a highish impedance at the receiver (or aerial transformer), I imagine that it picks up quite a bit less signal and interference than the aerial itself.

This it could be that the first case, with a 14 metre aerial of which 7 metres is in the interference field, picks up more interference than say the third case, in which the 5 metre aerial is above the interference field, but 8 metres of the 10 metre earth wire are within it. And sufficiently more that it more than offsets its greater signal pickup due to its greater aerial length.

A special case of the antistatic aerial was where the earth wire was screened in order to avoid interference pickup as it passes through the interference field. According to R&TVERB, doing this would cause a 3 to 4 dB drop in signal pickup but a bigger drop in interference pickup. That 3 to 4 dB number is an indication of the signal contribution from the earth wire.

Nonetheless, I suspect that more common were antistatic installations in which the earth return from the aerial transformer primary did pass through the interference field, nonetheless producing better signal-to-interference ratios than would be obtained with the simple arrangement where the feeder was simply a downward extension of the aerial rod.

Perhaps better would be to mount the vertical on a pole sufficiently removed from the house to be outside of the interference field, with the aerial transformer at ground level, with the screened feeder then running (perhaps underground) to the house.

In fact this kind of arrangement is more or less what Wellbrook recommends in respect of its UMB 130 “Universal Magnetic Balun”. This is of the isolating type, allowing a separate primary earth at the aerial end and can be used with longwire (and presumably vertical) aerials as well as with dipoles. It matches to 50 0hm coaxial cable rather than screened twin. With domestic receivers with high impedance aerial inputs, another balun could be used at the receiver to provide a step-up transformer. (In this case the balun is actually deployed as a unun.)


Cheers,

[G8HQP Dave]

I think all this goes to show that what we call 'the antenna' and what nature actually uses as the antenna are not necessarily the same thing, although in most cases there will be some overlap.

[LyntonP]

A great deal of useful information has come out of my original question. Thanks for all the replies.
I have been doing some experimentation of my own, and I feel I now have a good (but not very surprising) result.
First I built a 40 inch magnetic loop aerial. The results with this are stunning. Interference from electrical noise can be eliminated completely by rotating the aerial, and careful adjustment of the tuning capacitor makes it very sensitive as well as selective. The downside is it’s physical size and the fact that the Boss wasn’t too pleased about the machine vice on the dining table (see photo).
Next I came across a design for a much smaller loop, which I tried and found it to be almost as good. I decided to turn it into a finished project that could sit atop of the radio in the lounge without too many complaints. Inspired by David G4EBT wooden test equipment enclosures I also had a try at using box joints with some success, though comments were passed that my tuning capacitor box resembled a coffin or a container for the family dogs ashes! Unperturbed I varnished it and I think it looks ok. With a little extra capacitance switched in Radio 4 on LW is crystal clear, and I can even find Manx radio on MW.
Yesterday a neighbour helped me to erect a random length long wire aerial. I managed to fit in about 100 foot of wire. Today I completed the final hook up and I am very pleased with the results. It is around gutter height but in the clear. Both LW and MW have very little electrical interference and stations tune in without any of the annoying “hiss” detracting the signal.
I suppose this was the type of aerial that the set was built for (1937 Murphy).
Looking forward to tonight to see what stations we can hear.
Lynton
PS having trouble with the photos. I will try to attach them separately.

[LyntonP]

Photos I hope.
Lynton

[DoubleWound]

I'm finding Lynton's post extremely informative and congratulate him on a fine piece of work.

A knowledgeable member of this forum has often advised me that loop aerials can be very effective.

[dave walsh]

I visited a friend who lives between Bury and Bolton last week. He has had a large, home built, loop aerial [probably a metre across as well] for some time. It cost very little! There is no doubt that using one of these can prove amazingly effective. He's just modified a new shed into a purpose built Radio Room so he doesn't have to worry about spouse "reaction" any more. The interior is lined and insulated with some excellent pine cladding off-cuts, coincidentally obtained from a large building project located near my Ramsbottom address and re-cycled for free, just for the asking! Very satisfactory.

Dave W

[G6Tanuki]

Lynton, It's great to hear that you're making good progress in getting a better signal, while putting your carpentry/joinery skills to good use and learning at the same time! This is really what the hobby's all about - combining theory and practice to achieve the desired outcome.

Indeed, you're inspiring me to roll my own 'tuned loop' - if only because I want to get a decent entertainment-quality signal from Radio Caroline when it's next active on 648KHz.

[Just don't expect me to build anything wooden - I seem to have a knack for always finding myself working against the grain!]