Hello Mike -
Thank you for the very long explanation!
Indeed, I already experimented with (unknown) ferrite rods but I'm just waiting here for new specified material (better) ferrites.
So I have time to search for more info...
Your mentioned link is one of the best I already found on the net.
In transmitting state the ui seems to fall to near 1. You can see it because the resonance frequency is going much higher (and that
will also increase harmonics)!
I'm not sure if a ferrite rod is a dipole? There is another structure possible: Ferrit-loaded helical antenna.
Unfortunately that is a kind of black art. Not much on the net to find.
The very low radiance resistance of the ferrite rod antenna is not the main problem. You must match the impedance to the
transceiver. That is easier if the antenna is an integral part of the system end amplifier, TX-RX switch and pre-amp.
If I understood you right, the "miracle whip" is not a antenna, more an impedance transformer. Whereas the typical ferrite rod
antenna is an autotransformer by itself - simply by adding or tapping another coil on the rod.
regards -
Henry
"Mike Kaliski" schrieb im Newsbeitrag ...
|
| "Henry" wrote in message
| ...
| Hello group -
|
|
| My new interest is ferrite rod antennas.
|
| I'm looking for a (possible) interesting doc:
| UK magazine Practical Wireless, April 2000, pages 38 and 39 "An
| Experimental Ferrite Rod Transmitting Antenna" by Richard Marris G2BZQ
|
| Seems not on the net and the author doesn't have an email address or is
| gone.
|
|
| Would be nice if someone can send it per email.
|
|
| Anybody interested in ferrite antennas can contact me for info sharing.
|
|
| Best regards -
| Henry Kiefer
|
| Henry,
|
| I vaguely recall reading this article also. As I recall it was claimed that
| it was possible to use ferrite quite successfully to receive and transmit on
| frequencies up to 7MHz or 40 metres. I believe the antenna used a couple of
| six inch ferrite rods side by side with the old medium wave and long wave
| windings removed and perhaps 15 or 20 turns of wire to resonate on 40 metres
| wound over a sliding card sleeve. The sleeve was made loose enough to slide
| along the ferrite rods to achieve the best point of operation.
|
| I would suggest getting a couple of old ferrite rods and experimenting with
| some wire and a capacitor for resonance.
|
| The problem with ferrite is that it tends to be very lossy in transmitting
| applications. The principles that concentrate received signals in a loop of
| wire wound around the ferrite rod, result in transmitted signals becoming
| concentrated in the ferrite rod, which then absorbs a lot of the RF energy
| and reradiates it as heat. One or two six inch ferrite rods should be okay
| for transmitter powers up to 10 watts.
|
| The reason for using ferrite rods was to develop a small antenna with
| similar properties to a dipole. One that could be rotated in the shack to
| null out interference etc. Transmission efficiency will be very poor, but
| the directional properties and the fact that you only need to radiate
| milliwatts to work thousands of miles using CW may mean this type of antenna
| will work fine for you.
|
| One thing it wasn't, was a type of miracle whip. I have built one of those
| following instructions on the web and it works okay at QRP powers from 3.5
| MHz to 28 MHz. The transmission efficiency is rubbish, but it gets some sort
| of a signal out and is fine for receiving. The miracle whip type of antenna
| uses a wire wound ferrite toroid as a matching autotransformer to match the
| impedence of a short whip to 50 ohms.
|
| Try the link below for some more info on how ferrite works for receiving and
| transmitting antennas
|
|
http://www.st-andrews.ac.uk/~jcgl/Sc...rt7/page5.html
|
| This page suggests transmitter powers of less than a watt be used with
| ferrite, but I think it depends on the heating effects you get with the rods
| you end up using. There are many different formulations used in making
| ferrite rods and toroids and some rods will work very much better than
| others in this type of application.
|
| Mike G0ULI
|
|