Extending the range of a Discone antenna down to 3.6 MHz

Useful information regarding antennas for SDR products.
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vk3alb
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Post by vk3alb » Fri Feb 08, 2019 8:11 pm

Thank you both. An excellent experiment.

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ON5HB
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Post by ON5HB » Fri Feb 08, 2019 8:46 pm

Did you try to transform the 50 Ohm Discone antenna to a higher impedance?

The Hi-Z isn't 50 Ohm but 1000 Ohm, the voltage/amp levels going into the Hi-Z should be more suitable for it.

I do not know what the impedance is outside it's design frequencies but it may be worth trying to calculate it and make a transformer.

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

Post by glovisol » Fri Feb 08, 2019 10:25 pm

Hi Bas, there is a TOTAL MISUNDERSTANDING which I perceive from your questions!!! How could you think I would connect a 50 Ohm downlead to a HI Z 1 Kohm input with no matching?

Please look at the posted photos (even those posted before): I have always connected and tested the Discone antenna (50 Ohm) connected to the 50 Ohm coaxial input of the RSPduo using a 50 to 50 Ohm (1:1) toroid transformer. Up to now I have NEVER connected the 50 Ohm Discone coaxial output cable to the balanced HI Z 1 KOhm input of the RSPduo. I will try this connection later on.

In all the tests I have used the 135 m Beverage antenna connected to the balanced HI Z input and the Discone antenna to the 50 Ohm coaxial input.

I take this opportunity to upload PC screens of Discone & Beverage @ 3.6 MHz

Best regards,

glovisol
Attachments
Discone with Xfrmr @ 3.6 MHz.jpg
THIS IS THE DISCONE ANTENNA UNDER TEST
Discone with Xfrmr @ 3.6 MHz.jpg (198.1 KiB) Viewed 3120 times
Beverage @ 3.6 MHz.jpg
THIS IS THE BEVERAGE FOR COMPARISON
Beverage @ 3.6 MHz.jpg (197.89 KiB) Viewed 3120 times
RSP inputs.JPG
Antenna connections to the RSPduo
RSP inputs.JPG (144.39 KiB) Viewed 3120 times

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ON5HB
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Post by ON5HB » Sat Feb 09, 2019 10:44 am

Thanks a lot for making it clear, I was totally confused and puzzled.

Now it makes perfect sense.

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

Post by JMG » Sat Feb 09, 2019 11:21 am

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

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

Post by glovisol » Sat Feb 09, 2019 12:03 pm

BUILDING A STABLE 1:1 LOW CAPACITANCE TRANSFORMER - 1

The low capacitance transformer needs a stable configuration. I decided to build a suitable housing which keeps input & output common terminals insulated from each other. Here below the building sequence. I used a thick walled PVC pipe.
Attachments
1. Gluing the windings.JPG
1. Gluing the windings.JPG (83.38 KiB) Viewed 3095 times
2. Preparing the connectors.JPG
2. Preparing the connectors.JPG (128.15 KiB) Viewed 3095 times
3. Connectors ready for assembly.JPG
3. Connectors ready for assembly.JPG (143.82 KiB) Viewed 3095 times

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

Post by glovisol » Sat Feb 09, 2019 12:04 pm

BUILDING A STABLE 1:1 LOW CAPACITANCE TRANSFORMER - 2

I have provided a proper housing for the 50-to-50 Ohm low capacitance transformer and for the 550-to-1 Kohm low capacitance transformer as well.
Attachments
4. Transformer being assembled.JPG
4. Transformer being assembled.JPG (75.59 KiB) Viewed 3085 times
5. Transformer in operation.JPG
5. Transformer in operation.JPG (127.93 KiB) Viewed 3085 times
6. RSPduo equipped with HI Z & 50 Ohm XFRMRS.JPG
6. RSPduo equipped with HI Z & 50 Ohm XFRMRS.JPG (76.14 KiB) Viewed 3085 times

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sdrom33
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Post by sdrom33 » Sat Feb 09, 2019 1:25 pm

JMG it seems the discone is working well to me!

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glovisol
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Location: Piedmont, Italy

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

Post by glovisol » Sat Feb 09, 2019 2:15 pm

The 20 m band really opened up today, to make me appreciate my new Discone antenna!

Hi JMG, could it be the trapped whip on top to work so well?
Attachments
Discone total.JPG
Discone total.JPG (39.01 KiB) Viewed 3075 times
Discone closeup.JPG
Discone closeup.JPG (44.73 KiB) Viewed 3075 times
14 MHz propagation really opened up today for my Discone!.jpg
14 MHz propagation really opened up today for my Discone!.jpg (88.03 KiB) Viewed 3079 times

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ON5HB
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Post by ON5HB » Sun Feb 10, 2019 1:41 pm

I found this bit of information and they state:
Additional vertical element on discone

Often discones will be seen with an additional vertical element attached to the top of the antenna. This is often the case when they are used as a scanner antenna.

This additional vertical element on the discone helps to extend the lower frequency response for the overall antenna, giving improved performance at lower frequencies.

The downside to the addition of the vertical element is that it can reduce the efficiency at higher frequencies.
Here is the link: https://www.electronics-notes.com/artic ... basics.php

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