RTL-SDR as a rf analyzer?

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pljevljak
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Joined: Sun Nov 24, 2019 11:26 pm

RTL-SDR as a rf analyzer?

Post by pljevljak » Sun Nov 24, 2019 11:50 pm

Hi all,
As I am relatively new to this device, I hope you will forgive me if my question was answered before or is something obvious😁. Now, I’m interested if it is possible to use the sdr as a simple spectrum analyzer for radio transceivers, in my case the Baofeng uv-5r, simply by adding attenuator between them. Is it possible to realize it that simple and if is, what attenuation value should be used? Also I couldn’t find infos about input impedance and max input power of sdr, so I can’t figure out any additional requirements for this “device”.

rtlsdrblog
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Re: RTL-SDR as a rf analyzer?

Post by rtlsdrblog » Mon Nov 25, 2019 9:36 am

Definitely possible to monitor the output of a Baofeng on the RTL-SDR with sufficient attenuation.

Max input power is 10dBm but in practice you'll want much lower power input than that.
Input impedance is 50 Ohms.

pljevljak
Posts: 3
Joined: Sun Nov 24, 2019 11:26 pm

Re: RTL-SDR as a rf analyzer?

Post by pljevljak » Mon Nov 25, 2019 12:13 pm

As I thought. Thank you for reply!

radiolistener
Posts: 76
Joined: Thu Jan 25, 2018 10:48 pm

Re: RTL-SDR as a rf analyzer?

Post by radiolistener » Mon Nov 25, 2019 3:54 pm

yes, you're needs 40 - 60 dB attenuator which can handle 20-30 W power.

40 dB should be safe for 5 W baofeng output, but signal may be still too strong and may overload the input.
So, it's better to use 60 dB attenuator. Or you can combine 40 dB 20 W attenuator with a small 20 dB 2 W on the output of first attenuator.

pljevljak
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Joined: Sun Nov 24, 2019 11:26 pm

Re: RTL-SDR as a rf analyzer?

Post by pljevljak » Tue Nov 26, 2019 12:35 pm

Yes, I came up with same specification, but it looks like 60dB 50w attenuator with sma connector is almost impossible to find, at least for a reasonable price...😕

hotpaw2
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Re: RTL-SDR as a rf analyzer?

Post by hotpaw2 » Tue Nov 26, 2019 4:14 pm

For 60 dB or more attenuation, try transmitting into a small 50 Ohm dummy load (with the required power rating). Put another small dummy load at the end of a coax plugged into your SDR. Then experiment with how close or far apart the 2 dummy loads can be placed while still delivering sufficient power to produce a visible spectrum on the SDR receiver software. This works because most dummy loads and/or their coax connections leak a tiny amount of RF through or on their shielding. For lower (milliWatt, etc.) transmit power levels, you may need a very short antenna instead of a dummy load on the SDR.

radiolistener
Posts: 76
Joined: Thu Jan 25, 2018 10:48 pm

Re: RTL-SDR as a rf analyzer?

Post by radiolistener » Tue Nov 26, 2019 5:37 pm

pljevljak wrote:
Tue Nov 26, 2019 12:35 pm
Yes, I came up with same specification, but it looks like 60dB 50w attenuator with sma connector is almost impossible to find, at least for a reasonable price...😕
https://www.aliexpress.com/item/32889026374.html

https://www.aliexpress.com/item/32854048582.html

https://www.aliexpress.com/item/32827240215.html

You can use high power 40 dB attenuator with low power 10 or 20 dB 2W attenuator.

For example 40 dB + 10 dB = 50 dB

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