LNA for stock antennas

Discuss commercial and home made antennas.
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Jekko
Posts: 26
Joined: Wed Oct 17, 2018 9:39 am

LNA for stock antennas

Post by Jekko » Wed Oct 17, 2018 9:46 am

Hi all,
I am an happy user of the rtl-sdr v3, with "stock" dipole antenna (this https://www.rtl-sdr.com/using-our-new-d ... tenna-kit/)

Unfortunately, i live in a city, in the middle of other houses, and i cannot place the antenna on the roof so the best that the antenna can do is quite few.

I hear mostly the 120-160Mhz band. Do you think that if i buy the LNA and i combine it with the stock antenna, i should get some improvement in the recepition?

If it helps, i would buy this LNA: https://www.rtl-sdr.com/product/rtl-sdr ... e-powered/

I am open to all indoor (cheap) solutions. DIY is fine (i am planning to build the planar disc too)
Thank you very much!

rtlsdrblog
Site Admin
Posts: 2323
Joined: Mon Nov 19, 2012 11:54 pm

Re: LNA for stock antennas

Post by rtlsdrblog » Thu Oct 18, 2018 7:05 am

Adding an LNA in this situation isn't going to help much at all, and may make things worse.

An LNA helps if you have long coax runs (overcomes the coax loss), and at higher UHF frequencies where the noise figure becomes more important.

You really need to work on the antenna positioning first.

Jekko
Posts: 26
Joined: Wed Oct 17, 2018 9:39 am

Re: LNA for stock antennas

Post by Jekko » Fri Oct 19, 2018 3:12 pm

Thank you very much for the reply!

Do you think that 88-108 Fm trap could help or is it useless in my case?

JEL
Posts: 131
Joined: Wed Feb 07, 2018 2:08 am

Re: LNA for stock antennas

Post by JEL » Fri Oct 19, 2018 6:15 pm

Jekko wrote:
Fri Oct 19, 2018 3:12 pm
Do you think that 88-108 Fm trap could help or is it useless in my case?
That thing you WANT! :)

When I got that myself it made a HUGE difference (improvement)

I wish there were more filters available actually.
BCFM is only 1 annoying band. There are also other digital broadcast-bands that are quite powerful as well as telephones and Tetra-stations.

In short; filtering bands you do NOT want to listen to (especially if they're strong in power at your location) is generally a good idea.

rtlsdrblog
Site Admin
Posts: 2323
Joined: Mon Nov 19, 2012 11:54 pm

Re: LNA for stock antennas

Post by rtlsdrblog » Fri Oct 19, 2018 8:39 pm

rtlsdrblog wrote:
Thu Oct 18, 2018 7:05 am
Adding an LNA in this situation isn't going to help much at all, and may make things worse.

An LNA helps if you have long coax runs (overcomes the coax loss), and at higher UHF frequencies where the noise figure becomes more important.

You really need to work on the antenna positioning first.
For the 120 - 160 Mhz band, the BCFM filter could help quite a bit. But it does depend on if you are receiving strong broadcast FM in your area. Tune to the BCFM band and see how strong the signals are. If they are strong (and they are for most locations since the TX power of broadcast FM is quite strong), then the BCFM filter will probably help.

snn47
Posts: 179
Joined: Tue Dec 27, 2016 11:00 pm

Re: LNA for stock antennas

Post by snn47 » Sun Jan 20, 2019 6:41 pm

The disadvantage of having a very broadband antenna with preamplifier is that without filter/frequency selective antenna the receiver and or the preamplifier in the antenna may be overloaded. This means the active components cannot process all signals with the same factor, e.g. weak and stong signals by 10 dB. This is called Intermodulation or IM, which will produce additional signals that are not present at the antenna (e.g. IM 3rd order 2*f1 +f2 and 2*f2 -f1 in case you have only IM of 2 strong sigals). You can identify this if you add a 10 or 20 dB attenuator. If you have IM than all signals that were at least a bit stronger than 10 or 20 dB in signals strength are gone you have IM.

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