Hi Marcel the original idea came from a Pat Hawker Technical Topics column. It was originally in a Canadian BC Journal and recommended for short free standing MW BC antennas. We  did the experiments you found in the web pages on 136kHz. Gary up in Preston made one too. The problem with them is the windage of the spiral, Garry G4WGT had his destroyed in a light gale.  They can work but as our experiments showed top-load capaitance is far more effectinf at reducing ground loss and increasing the efficiency. Hence the additional tests with capacitance added above the spiral. wirespacing was 5 to 10 cm from memory and not too critical, yes it you need the inductance you can wing out below the stays and back in again above then and get 4 times the inductance. You will not need so much inductance at 475kHz. It is also possible to helically wind the vertical. The gain achieved is relatively low measured at an increase in Rrad of about 10%.

 

Best Wishes

Alan

G3NYK

----- Original Message -----

From: Marcel Bos

To: [email protected]

Sent: Monday, June 01, 2015 10:11 AM

Subject: LF: Top loaded vertical spiral antenne

Members,

My backyard is in the city 8 x 8 m.  My intention is to do some experiments on 472 khz.

Ready: RX converter 0-500 khz 10 mhz osc. and K3, RX ant. pa0rdt whip and receiving loop

TX: GW3UEP 100 watt, RF meter, and variometer 30 uh -600 uh

Now i'm looking for a antenne. Found a article from Finnbar EI0CF and Alan G3NYK about the spiral toploaded vertical.

Has any body tryed this antenne, is the original article availble.

What is the distance between the wire's  of the spiral?

Also talking about a double spiral?

So who is gone help me out  ore has some better suggetions for a antenne in my backyard

http://www.xeropage.co.uk/g3nyk/spiraltop.htm#aerials

tnx in advanced

Marcel

PA9M