Extending the range of a Discone antenna down to 3.6 MHz

Useful information regarding antennas for SDR products.
glovisol
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Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

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

Post by glovisol » Mon Feb 18, 2019 4:50 pm

NO WHIP / WHIP DISCONE ANTENNA TESTS - 1

Antenna test was done as follows.

1) Tests were done between 17:00 and 17:30 local time or 16:00 to 16:30 GMT. This hour was chosen as propagation on 3.6 MHz is already good and there are plenty of signals on air. Time was restricted to 17:30, as later it becomes too cold and visibility deteriorates.

2) There was a friend on the roof who would remove / replace the whip on command.

3) Antenna was equipped with (a) one RF "bottle choke" just inside the roof, e.g. 2 m from the antenna UHF connector. (b) One RF choke done with 4 turns of the downlead coaxial cable wound on a ferrite arrester toroid. (c) The isolation, low noise transformer already described, connecting the lead-in to the Tuner 2 coaxial input of the RSPduo receiver.

4) Comparative testing between Beverage and Discone was done by switching between the Hi Z input (Beverage) of Tuner 1 and 50 Ohm input of Tuner 2 (Discone).

Here below and in following posts the resulting PC screens.
Attachments
1. Discone no whip 17_10.jpg
1. Discone no whip 17_10.jpg (188.6 KiB) Viewed 3090 times
2. Beverage 17_10.jpg
2. Beverage 17_10.jpg (191.23 KiB) Viewed 3090 times

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glovisol
Posts: 662
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

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

Post by glovisol » Mon Feb 18, 2019 4:52 pm

NO WHIP / WHIP DISCONE ANTENNA TESTS - 2
Attachments
3. Discone whip 17_22.jpg
3. Discone whip 17_22.jpg (194.77 KiB) Viewed 3088 times
4. Beverage 17 22.jpg
4. Beverage 17 22.jpg (193.53 KiB) Viewed 3088 times

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

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

Post by glovisol » Mon Feb 18, 2019 4:54 pm

NO WHIP / WHIP DISCONE ANTENNA TESTS - 3
Attachments
5. Discone no whip_17_30.jpg
5. Discone no whip_17_30.jpg (192.66 KiB) Viewed 3086 times
6. Discone whip 17 30.jpg
6. Discone whip 17 30.jpg (197.52 KiB) Viewed 3086 times
7. Beverage 17 30.jpg
7. Beverage 17 30.jpg (197.67 KiB) Viewed 3086 times

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ON5HB
Posts: 140
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Re: Extending the range of a Discone antenna down to 3.6 MHz

Post by ON5HB » Mon Feb 18, 2019 5:07 pm

What are we seeing?

As when I reply there are more pictures then we see in reading your post.

Anyway, your filenames make sense, so I could figure it out.

As I said, the whip lowers the reception range.
Without it 80m is gone, so the chokes work else it wouldn't make any difference and the coax would have done reception.

But the discone is vertical, so a direct comparisment is not real valid, some signals are better vertical others better horizontal.
Real test would be DX signals as those tend to be non/less-polarised as short-distance.

To be honest, I do find all levels rather low, as my Icom7300 and my websdr have far stronger signals.
Are you sure the beverage is working properly? Noise levels here are easily S7-9 at those times, nowhere near as low as yours.

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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 » Mon Feb 18, 2019 5:11 pm

Come on, Bas, I did the measurements on purpose at this time of the day because signals at this frequency are there, but not as strong as they normally are later in the evening. If I chose a full strength propagation time, then I could have had signals coming in from every pore, ruining my measurement.

The comparison with the Beverage is NOT IMPORTANT per se, it just tells us that SIGNALS ARE PRESENT and therefore the test on the Discone antenna is valid.


Now that the whip is back in, I shall do return loss measurements with the Network Analyser and report the results.

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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 » Mon Feb 18, 2019 5:19 pm

How long is your beverage?

As the signal level is far to low for a beverage, they are known for their better reception then e.g. a dipole.

Unless it's not meant to receive 80m.

I'm trying to figure out why the discone needs to do 80m if you have a beverage. It simply makes no sense.

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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 » Mon Feb 18, 2019 5:35 pm

Bas, I installed the Discone ONLY TO RECEIVE FROM 100 MHz and up and this the antenna achieves very well: I receive daily plenty police/aircraft/ 2m band hams.

It happened that BY CHANCE I discovered that I could receive acceptable signals (even if 20 to 25 dB lower than the Beverage) down to 3.6 MHz, provided I used an isolation transformer as I have described in the previous posts.

This is the reason why I started this thread, so that I could let know to other guys, who live in places where they can put up a small Discone only, that perhaps they could use it in HF, along with receiving VHF & UHF.

The second reason was that I am no real expert in antennas and hoped to find helpful guys on the Forum who would help me to understand what it is happening here.

I have described my Beverage elsewhere, it is 135 m long and in evenings of good propagation, like in these days, I need attenuators and, if I am not careful, I could risk "RSP roasting", just look here:

https://www.sdrplay.com/community/viewt ... f=5&t=4124

Have a nice evening!

glovisol

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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 » Mon Feb 18, 2019 5:46 pm

That makes sense.

A 135m beverage is basically good for 40m but not 80 or even 160m
That explains the low signal levels.

As for roasting the box, nah, you won't roast it.
I put 1 KW next to it, sure it passes a No-Elec 125MHz upconverter, but it never got roasted.

The signals I give it to handle are a lot higher, trust me they are.
I do not dream of touching my reception-antenna-cable during a 1KW transmission.

The boxes are well protected and I do not recommend anybody doing what I do, but they do not burn that easy....certainly not over an antenna when there is no transmitter near to it, like less then 50-100 meters.
My antenna's are less then 3 meters apart :lol:

(Do not try this at home folks!)

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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 » Tue Feb 19, 2019 7:02 pm

DISCONE ANTENNA SWR PLOTS

Antenna plots with vertical whip mounted above the Discone. Network Analyser connected to the antenna coaxial output to the RSP. Comments invited.
Attachments
Discone plot 4.jpg
Discone plot 4.jpg (68.7 KiB) Viewed 3028 times
Discone plot 3.jpg
Discone plot 3.jpg (73.51 KiB) Viewed 3028 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 » Wed Feb 20, 2019 9:51 am

DISCONE ANTENNA SWR PLOTS with SWR NULL FREQUENCIES
Attachments
Discone plot 3.jpg
Discone plot 3.jpg (116.16 KiB) Viewed 3007 times
Discone plot 4.jpg
Discone plot 4.jpg (107.2 KiB) Viewed 3007 times

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