What’s going on here ?? Receiving but no antenna

Useful information regarding antennas for SDR products.
illllm
Posts: 56
Joined: Wed Jan 23, 2019 10:26 pm

What’s going on here ?? Receiving but no antenna

Postby illllm » Sat Feb 09, 2019 2:34 am

https://youtu.be/eIzoAdcMejQ

Very odd behavior. The isolation transformer seems to pick up transmission from 800 miles away and.....I am indoors.

Scratching my head as to how this is possible. That’s Friday night oldies from a station in Lebanon, Tennessee and I am in Virginia.

Also trying to connect the loop with one hand is not easy :P

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illllm
Posts: 56
Joined: Wed Jan 23, 2019 10:26 pm

Re: What’s going on here ?? Receiving but no antenna

Postby illllm » Sat Feb 09, 2019 2:39 am

Sorry that is the mini whip. First no antenna, then attached whip, noise floor increased, then adder power noise floor rose but signal not much, then completely disconnected but signal was strong. I increased the volume a bit later on.

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illllm
Posts: 56
Joined: Wed Jan 23, 2019 10:26 pm

Re: What’s going on here ?? Receiving but no antenna

Postby illllm » Sat Feb 09, 2019 2:41 am

Perhaps the coils are magnetically coupled to the metal server case they are sitting on? :?: will try it on the carpet tomorrow.

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illllm
Posts: 56
Joined: Wed Jan 23, 2019 10:26 pm

Re: What’s going on here ?? Receiving but no antenna

Postby illllm » Sat Feb 09, 2019 1:09 pm

still same..even on the carpet it picks up many shortwave stations.

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g1hbe
Posts: 475
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: What’s going on here ?? Receiving but no antenna

Postby g1hbe » Sat Feb 09, 2019 1:19 pm

I've lost track - is it picking stuff up with nothing connected to the antenna socket, or with the balun connected?

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Andy

ON5HB
Posts: 124
Joined: Sat Dec 29, 2018 1:07 pm
Location: Heppen - Belgium
Contact:

Re: What’s going on here ?? Receiving but no antenna

Postby ON5HB » Sun Feb 10, 2019 1:52 pm

What happens if you shorten the open side?
As long-mid-wave antenna's in old transistor radio's used to have an antenna build on just a ferrite rod.
Typical working 0~3 MHz.

Have a look:

https://www.st-andrews.ac.uk/~www_pa/Sc ... page5.html

Maybe your core acts the same? Is the only logical explanation I can think off.

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Greetings,

Bas - ON5HB

Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: What’s going on here ?? Receiving but no antenna

Postby Roger » Sun Feb 10, 2019 5:17 pm

In order to receive a signal you need to have an antenna with two sides. A dipole, for example, has two wires connected to a feedline (like twinlead or coax). A vertical antenna has one element (wire, mast or whip) and uses a ground or counterpoise as the other.

So what is happening in your case when you only have a balun connected to your RSP and no antenna attached to the balun? You still have an antenna system but it is a poor one and only able to receive very strong signals. One side of the antenna is the USB cable and the other side is the short connecting wire from the RSP2 circuit board to the SMA terminal and your attached balun. This poor antenna will pickup strong signals and local noise (RFI).

USB cables vary considerably in quality. The best ones have the wires twisted and shielded with an outer shield encasing all the wires. They also have a quality toroid but these are generally used to reduce cable radiation above 30 MHz. Tripp-Lite makes quality cables but even these should have external toroids (Mix 31 works well) to reduce noise pickup on the HF bands. Here is what I use and it works well on HF.
.
.
Attachments
USB Cable.jpg
USB Cable.jpg (138.55 KiB) Viewed 2856 times

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illllm
Posts: 56
Joined: Wed Jan 23, 2019 10:26 pm

Re: What’s going on here ?? Receiving but no antenna

Postby illllm » Sun Feb 10, 2019 9:19 pm

Thank you all for responding. My USB cable is shielded and its exactly as shown in the picture above including the clamp on torrid cores. Yes its picking up stations with just the 1:1 connected.

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Mike2459
Posts: 314
Joined: Mon Jul 24, 2017 8:24 pm

Re: What’s going on here ?? Receiving but no antenna

Postby Mike2459 » Sun Feb 10, 2019 11:33 pm

Screen shot of AM Broadcast Band at 1830 local time received with 2 inch (5.08cm) hookup wire antenna connected to the Hi-Z port (P terminal ) of the RSP2.
Attachments
2 inches of wire.JPG
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Mike2459
Posts: 314
Joined: Mon Jul 24, 2017 8:24 pm

Re: What’s going on here ?? Receiving but no antenna

Postby Mike2459 » Sun Feb 10, 2019 11:38 pm

Hi-Z Port connector disconnected:
Attachments
Capture.JPG
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