Aerials for old domestic valve sets.

[LyntonP]

Originally Posted by G6Tanuki

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

The 40 inch loop was the easiest of the two by far. Simple to make without any complicated joints, easy to thread and keep the wires tight. If you search on this forum there are details.
The smaller loop did need one joint, but drilling all the holes was tedious and the threading of the wire and getting good tension took a long time.
I have since heard of a design for a 20 inch loop, but can’t find any details as yet.
I have also seen them made from plastic pipe. I just used what I had to hand.
Have a go I’m sure you will not be disappointed.
Lynton

[G4YVM David]

Originally Posted by Ian - G4JQT

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.

The voice of reason.

[Ian - G4JQT]

Thanks David. But the thread has moved on to tunable loops. They are VERY effective at providing quite large wanted signals while their directivity can greatly reduce interference if it's coming from one direction. They can also null out a strong station on the frequency you're tuned to, again if the differences in direction are significant.

We used them professionally to receive various MF stations in a location where beverage antennas were not possible. Each loop was fixed-tuned for a particular channel, and orientated do minimise co-channel interference. They were very effective.

For anyone thinking of making one who is not familiar with them, there's nothing magic about the dimensions, although approximately 1m square is a good compromise between size practicality and directional properties. There are designs with a FET buffer amp rather than the one-turn coupling loop. I'm minded to think the coupling loop is to be preferred, because although it gives lower output it has lower noise, requires no battery and won't overload!

Other sizes will require adjusting the number of turns in the main coil and/or adjusting the value of the tuning capacitor (maybe with a padder or a trimmer) to get full band coverage.

Experimenting with the number of turns in the coupling loop may be worth experimenting with too depending on the size of the main loop and the aerial/earth impedance of the radio it's used with.

[jsbhavsar]

In India, all typical valve radio sets connected to an inverted-L aerial system for receiving.

Check a installation in photo here:

http://mysoreanmusings.blogspot.com/...magic-eye.html

I still have the fine copper mesh version last purchased 2002-2003 production of new ones since stopped. I have not heard anywhere in the world this type of extreme fine copper mesh 3 meters long being used for radio aerial. Even my Dad started with this setup in 1968 eventually replacing a few aerials over the years. Initially these were installed outside in balcony in open air for better reception. Only when bird troubles increased, these setups moved indoors with reduced performance as now the indoor RF due to flourescent tubes would add to.

The extreme fine copper strand of wire woven into a fine mesh / net probably acted a huge capacitance and helped boost the "high impedance" requirement for the aerial input.

Many times as a kid, I played with the earth socket and connected the earth to "mains earth" and saw improved performance.

[LyntonP]

I have been making some modifications to the random length single wire aerial over the past few weeks.
All of the aerial is now in the clear and somewhat higher than before. I also put a feed into the shed so I can connect it easily to the R600 which has the benefit of an S meter making comparisons with the G5RV more convenient.
Also the R600 tunes all the way from 0-30 Meg so I can compare signals on all bands.
Last Saturday evening I started on long wave and worked my way upwards.
I was pleasantly surprised to find far more LW and MW stations throughout Europe and The UK than I had ever heard before.
The station I often use for a benchmark is Manx Radio since I am right on the outer range of its coverage area. Now however it comes in at +10dB even during the day on the wire when it is all but inaudible on the 5RV, and at night gets up to +30dB or more.
Using an old MW station listing handbook it was easy to identify stations all over Europe, and I am told even American stations can be heard early in the morning.
Next I tried the wire on SW. I easily picked some all the stations I am familiar with but with much more noise. Switching back to the 5RV made them much clearer.
I constructed an earth rod driving a pipe around four foot into the ground. The results were disappointing since it seemed to make no difference to the received signal when using the wire.
My conclusions? Well it’s horses for courses I suppose. The wire was much better on long and medium wave, and the 5RV better on SW.
Onto the next loop or maybe a simple atu for the wire?
Lynton

[Skywave]

Originally Posted by LyntonP

I constructed an earth rod driving a pipe around four foot into the ground. The results were disappointing since it seemed to make no difference to the received signal when using the wire.
Lynton

That is a result that I have met at various locations - but not all - and have never decisively found the cause. My suspicions for that effect are:
1. The resistance between the surface of the earth rod and the soil is too high.
2. The conductivity of the soil is too low.
3. The RF resistance of the earth wire is too high: length of wire, its x-sectional area and type of material used for that wire.
4. An effective 'short-circuit' across that earth connection, commonly caused by capacitance between the radio and the earth connection of the mains plug and general capacitance between the case of the radio and the item that the radio is sitting on.
5. Any combination of items 1 to 4.

I would be interested to hear of experiences of this phenomenon and ideas to improve that earthing arrangement from other members here. An extensive 'earth mat' beneath the aerial wire is a common remedy, however that is often inconvenient to arrange if not impossible.

Al.

[Ian - G4JQT]

The poor performance of the G5RV on anything other than SW is expected. You could - just out of curiosity - connect the inner and outer together and connect it to the Hi-z/random wire input of the R600 with the earth connection. It will probably be noisier than the random wire, but you never know.