In an attempt to overcome my high LF noise level, today I made a small ferrite rod antenna and preamp for 472kHz which I've been trying out on RX. The ferrite rod was just a small 10mm diameter 60mm long rod (i.e. it is a small ferrite rod) tuned with a 365p variable capacitor and fed into an MPF102 gate at high impedance with the output fed to the FT817 via an emitter follower. At the moment the rod is sitting on the bed in the shack. Despite this, it is picking up WSPR from
DK7FC.
I shall have to try a larger ferrite rod next and try placing this remotely in the garden away from noise sources. For a first attempt this is encouraging.
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| The prototype used to receive DK7FC and G3ZJO |
UPDATE: later I tried the 60mm ferrite rod and preamp on 500kHz and copied
G3ZJO on several occasions.
7 comments:
Hello,
welcome to the world of small antennas :) That's nearly what I'm using here in Paris. In my kitchen I also copy DK7FC with a S/N of -12 dB.
You can find my schematic here : http://arp75.free.fr/PortailARP/blog.php?lng=fr&pg=3649&prt=1
In this page a small loop antenna is shown, but that is for HF reception.
You should try balanced ferrite antenna. I've never try by a found a pdf on that. I'll give more details about that later because I don't remember where I found it.
73
Why be small when you can go big!
http://www.sarmento.eng.br/Loop_Ferrite_Rod_Antenna.htm
David
Why not eliminate C1, R4, R5 ?
Yes indeed, those parts could probably go. This was just thrown together in a hurry yesterday!
Hello David,
this is still a very small antenna. But it's a good idea anyway :)
Hello Roger,
try your coil with Litz wire. Or just take a coil from a MW radio, that's work fine :)
Thiery.
Roger,
Did some test with it, one disadvantage is the directivety. One rule of the thumb is that signals mostly comes from directions your antenna is not pointed at. When change it, the signal will stop en another will come in from the direction you originally were listening...
I have intention to arrange an omni directional antenna with ferrite with also a small horizontal loop which should pick up the local noise and cancel it in the final antenna signal. There is PDF which inspired me this solution. It's the Furuno NX7H navtex antenna. It's normally placed on board vessels, where local QRM situation can be severe than at home.
Link : http://ebookbrowse.com/nx7h-furuno-pdf-d339418959
Do note the small print about counterwise windings and the small "loops" in drawing and PCB.
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