433 MHz spring antenna?

Thanks, guys - especially Grumpy_Mike!

As far as antenna tuning goes, whilst established wisdom may be that this is best done using an low power SWR meter in an anechoic chamber, that is not how the antenna is going to be used in the real world.

A radiated signal test outdoors, with no SWR meter in circuit, is very close to how the antenna is to be used in the real world so that will give the most accurate tuning and its really not that difficult to do and no expensive equipment required apart form the radio modules and a couple of canes.

The document that turboscrew pointed to from Hope, descrbes the classic methods of SWR antenna tuning and then says;

The best way to fine tune a remote transmitter antenna is by using the transmitter itself. Put an antenna on a spectrum analyzer {RSSI Meter ?} and try to keep other large metal objects out of the way. Find a place to locate the transmitter that is away from metal and a few feet away from the analyzer. Always locate the transmitter in the exact same spot when testing. If you have a desk that is wood, mark it’s position with a pencil or tape. If hand held, hold it in your hand just above the marking on the desk. Be sure to position your hand, and the rest of your body, the same way during each test. Take a reading of the power level, and tune the antenna to achieve maximum radiated power.

Sounds familiar ?

As far as antenna tuning goes, whilst established wisdom may be that this is best done using an low power SWR meter in an anechoic chamber, that is not how the antenna is going to be used in the real world.

I think you are missing the point here completely. If you tune up the antenna under ideal circumstances that will give the best results under all possible circumstances.

Have you ever been in an RF anechoic chamber? Have you ever worked in one? I have.

A RSSI Meter is not a spectrum analyzer. You use a spectrum analyzer when you want to tune an antenna for minimum harmonic radiation not maximum power output.

and try to keep other large metal objects out of the way.

Have you ever tried that, it simply does not happen except way out in the open with no man made structures for at least 5 miles. Such test houses do exist, but this is not an option for many.

In the old days of valve transmitters you could get a reasonable approximation of correct antenna tuning by looking for a dip in the PA anode current.... ( Iwas a radio ham back in the 60's, when transistors were unknown expensive super - modern stuff ).

And the tool you really need is a vector network analyser and some familiarity with the smith chart and vector
arithmetic.... Or even a vector voltmeter ( you don't see them much these days)

They're not cheap. Agilent ( used to be Hewlett-Packard) , Anritsu and Rhode&Schwartz all make good ones.

regards

Allan

I have trouble getting a 433 MHz link to work satisfactorily and it is clearly an antenna matter.
Therefore I opened up a Nexa transmitter, see the images.
The antenna consists o a loop ca 25x10 mm2 in parallell with a 14 turn coil.
The coil, however, is a spring made out of a magnetic material such as iron, steel or nickel.
I can't understand why they have selected such a material with high losses. It may of course be silver plated. Advantages are of course dimensional control and mechanical stability.
Can anyone explain why they selected such a material?
Thanks in advance
H

Seems to be the board of a keyfob. There is no real aerial inside those.
They only work short distances and the user has to hold it (user = aerial).
Leo..

Only the outer few micron matters at 433MHz, due to the skin effect, so the bulk material of the spring/coil
isn't important. The skin effect tends to equalize effective resistivities since less conductive metals have
a greater skin depth, so any metal will tend to work, so long as it doesn't tarnish/corrode.