Gary, G4WGT has done some experiments with this
sort of spiral top-load antenna on 136 kHz. Take a look at his web-site, page 6.
See link below.
I have done a comparison with WSPR on 630m between
my "standard" wire MF antenna and a short base-loaded vertical (not spiral
wound) with a capacity hat. The standard antenna was a 20m long (tee)
configuration with a horizontal section at 6m height and two topwires. The
antenna had a vertical centre feed wire, with a loading coil in a shed
under the mid point. The vertical section of the antenna is the only part that
radiates. This antenna had a capacity of about 220 pF
The vertical antenna was a 5m fibreglass fishing
rod with a capacity hat made from six 60cm long radials (wire coathangers!),
with a loading coil inside the garage about 2m up from the bottom. I didn't
measure the capacity of this antenna but I would expect it to be about 80 -100
I found that running the same RF power
(15W) to the vertical produced WSPR reports that were about 10 dB weaker
than the "standard" MF "tee" antenna. This performance could be improved by
simply running 10dB more power to the vertical antenna! I would imagine that a
spiral wound antenna would have a perfomance that would be one or two dB better
than a base-loaded vertical.
I didn't do any comparison of the two antennas on
receive, as I used a separate 60cm square tuned loop for reception on
There's a picture of the vertical antenna and
loading coil on my QRZ.com page.
73, Dave G3WCB IO80DI
----- Original Message -----
Sent: Monday, June 01, 2015 10:11
Subject: LF: Top loaded vertical spiral
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
TX: GW3UEP 100 watt, RF meter, and variometer 30 uh -600
Now i'm looking for a antenne. Found a article from Finnbar
EI0CF and Alan G3NYK about the spiral toploaded vertical.
body tryed this antenne, is the original article availble.
the distance between the wire's of the spiral?
about a double spiral?
So who is gone help me out ore has
some better suggetions for a antenne in my backyardhttp://www.xeropage.co.uk/g3nyk/spiraltop.htm#aerials