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

Useful information regarding antennas for SDR products.
ON5HB
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Re: What’s going on here ?? Receiving but no antenna

Postby ON5HB » Mon Feb 11, 2019 9:56 am

Mike2459 wrote: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.


MW stations are very strong, it's not uncommon you need to lower the input-gain a lot.
Mostly it's even enough to just hold something near the connector for it to pickup signals, not even being connected.

These bands are very hard to NOT pickup signals, that is how easy they are received.
At the same time, overloading happens pretty quickly.

Have you tried the 50 Ohm ports and reduce gain? Does the same happen?

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Greetings,

Bas - ON5HB

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

Postby illllm » Mon Feb 11, 2019 11:51 am

The broadcast is Shortwave from Tennessee.... :) oh never mind you were referring to Mike.

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Mike2459
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Re: What’s going on here ?? Receiving but no antenna

Postby Mike2459 » Mon Feb 11, 2019 5:22 pm

Have you tried the 50 Ohm ports and reduce gain? Does the same happen?


No, I haven't. I use the same antenna for NDB chasing. The 50Ω ports don't do as well down there, so I just leave it on the Hi-Z. It's not really a problem. Just wanted to point out the sensitivity of the high impedance.

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snet0311
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Re: What’s going on here ?? Receiving but no antenna

Postby snet0311 » Mon Mar 11, 2019 4:54 pm

Similar Problem on 40m at night. Very high noise floor on the RSP2 with stations i’ve never heard before between 7100-7200. But, i‘m using the RF-Out from my Yaesu FT DX-3000 connected to Ant. Port A. The Antenna is a conventional trapped multiband dipole by Kelemen (hi quality). I have to use the ATT with -18db to get rid of the odd stuff. Kind of weired...

73, Stefan
Last edited by snet0311 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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ON5HB
Posts: 124
Joined: Sat Dec 29, 2018 1:07 pm
Location: Heppen - Belgium
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Re: What’s going on here ?? Receiving but no antenna

Postby ON5HB » Sat Mar 16, 2019 3:08 pm

Hi Stefan,

If you overload the ADC it will start giving ghost signals.
There are a few options you may want to try:

1: Turn on broadcast etc notches, as regardless the band you are, strong signals mix into other bands if the level is too high.
2: Reduce the gain of the SDRplay a lot, typical 50% or less is a good value, unlike normal receivers, when overloaded you get ghost signals.

As the signal-to-noise is very high for SDR receivers there is no need to look at the noise bottom, just change the bottom by lowering it on your screen.
SDR's not actual lower it, just move the screen.

However keep in mind, overloading an SDR is bad, stay away from it (far away) by reducing the gain a lot.

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Greetings,

Bas - ON5HB


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