Extending the range of a Discone antenna down to 3.6 MHz

Useful information regarding antennas for SDR products.
glovisol
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Location: Piedmont, Italy

Re: Extending the range of a Discone antenna down to 3.6 MHz

Postby glovisol » Sun Feb 10, 2019 2:58 pm

DISCONE ANTENNA ANALYSIS - IT'S NOT THE DISCONE, IT'S THE WHIP

Discone antenna dimensions are approximately as follows:

Top hat diameter D = 82 cm
Antenna element length Ls = 120 cm
Antenna height Lv = 105 cm

Reverse engineering these dimensions gives an approximate lower cutoff frequency of between 70 and 80 MHz. In effect the antenna pulls in Aircraft Band signals and 2 m Amateur Band signals much better than the internal whip I have on my desk and of course it must be as dead as an old shoe down at 3.6 MHz. But....but on top, above the top hat, the antenna has a whip 1.5 m long above a vertical section obviously housing a trap. This whip acts as a vertical element above the ground plane formed by the Discone's top hat and this is what must pick up (very well, I must say, considering its dimensions) the HF signals.

HI Bas, I see we had the same idea....in any case as a stand by all around antenna, once the noise is properly isolated, this Discone can hold its own!

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Roger
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Joined: Fri Dec 29, 2017 7:59 pm

Re: Extending the range of a Discone antenna down to 3.6 MHz

Postby Roger » Sun Feb 10, 2019 4:19 pm

JMG wrote:@glovisol
The discone itself NEVER will receice any reasonable signal at low frequencies! It is much to small compared to the wavelength.


JMG - I agree with you. The receiving element of this antenna is actually the outer shield of the transmission line. Much like the PA0RDT mini-whip (so called e-probe) which picks up the signal on the outer shield as well.

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glovisol
Posts: 339
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Extending the range of a Discone antenna down to 3.6 MHz

Postby glovisol » Sun Feb 10, 2019 6:44 pm

I am glad general consensus has been reached on this matter!

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glovisol
Posts: 339
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Extending the range of a Discone antenna down to 3.6 MHz

Postby glovisol » Mon Feb 11, 2019 8:01 am

Well.......to summarise there are three different theories on the carpet here about the unexpected but remarkable operation of the model D-130 Discone, without forgetting there is a 15 to 20 diB difference with the Beverage:

1) It is caused by the coaxial cable downlead acting as part of a capacitive hat antenna,
OR
2) It is simply the topmounted & trapped vertical whip which picks up signals in the HF band and delivers them to the RSP,
OR
3) it is a mixture of the two operating modes.

It would be most interesting to find out which is the valid theory. This is easy, just go on the roof and remove the whip, but cannot be done now, as I have plenty snow there. This I will do as soon as the roof is clean again and report back

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ON5HB
Posts: 53
Joined: Sat Dec 29, 2018 1:07 pm
Location: Heppen - Belgium
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Postby ON5HB » Mon Feb 11, 2019 10:03 am

My money is mostly on the coax and some effect from the whip.

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Greetings,

Bas - ON5HB


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