Once again I've realized that I don't know enough, and therefor I'd like to ask this question considering the use of RTL-SDR blog's USB Dongle v3 and the Wideband LNA & FM Broadcast Filters that are sold in the RTLSDRBlog store.
I recently got my RTLSDRBlog Wideband LNA and the FM Broadcast Filter to be used with my RTL-SDR Dongle v3. However, I'd like to ask a question regarding the signal chain before I plug the LNA in and enable the bias tee, let alone do it the wrong way ...
This is from the official RTLSDRBlog Dongle v3's manual page ( https://www.rtl-sdr.com/rtl-sdr-blog-v- ... ser-guide/ ) :
That's a no-brainer. However, I'm using the antenna kit supplied with the v3 USB dongle kit. And so, unless I'm getting it all wrong, the suggestion is to insert the LNA right before the antenna ( = before the coax cable long run that's between the USB receiver and the actual antenna)?To make things clearer: DC Short Antenna -> LNA -> Coax -> V3(bias tee on) is absolutely fine.
What's not good and makes no sense anyway is DC Short Antenna -> Coax -> V3(bias tee on).
DC Short Antenna -> Coax -> V3(bias tee off) is fine.
How about the Broadcast FM Band-Stop Filter? Should it be right next to the LNA, or right next to the USB receiver dongle in the signal chain? Any tips on that? Obviously, if in some cases the FM Filter needs to be *before* the LNA, there are no other options than to add the FM trap first in the chain, counting back from the antenna ...
As in, the signal chain being:
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[[ANTENNA]] => [[LNA and/or the FM Filter]] => [[Coax cable run to the dongle]] => [[The antenna input of the USB receiver dongle]]
There is a question in the comments and a reply from an admin considering the question at https://www.rtl-sdr.com/new-products-in ... nclosures/ :
The given answer was:Where is the best place to put the FM Trap filter? In between the antenna and the LNA or in between the LNA and the receiver? I’ve see both answers on the Internet. What’s your point of view?
Thanks for your help.
However this does not clarify whether i.e. the FM Filter should be in the signal chain right next to the LNA unit, or right next to the RTL-SDR dongle's input (= after the antenna, LNA and the coax cable run).It depends. If your RF environment has extremely strong FM signals that are strong enough to overload the LNA itself, then put the filter in front of the LNA. If it’s not overloading the LNA, put it after to reduce the filter insertion losses.
If you’re not sure, try with the filter after the LNA first, and if you don’t see any overloading issues (signal images etc), then leave it that way. If there are images, you need to put it before the LNA.
I'm trying to figure out what would be the best signal chain setup. Should the Broadcast FM filter and the LNA be right next to each other in the receiver signal chain?
I'm trying to use the "logic" here that every centimeter/inch of a [coaxial] cable run means more potentially added RF input ( = interference ... ). In which case, one solution would likely be to get rid of the additional coax cable altogether and try to use as straight-as-possible connection between the USB dongle and the dipole (in other words: to use just the short cable that's attached to the dipole kit's antenna, and ditch the extra coax run altogether).
Also, please raise your voice if the Dipole Antenna Kit that's supplied with the RTLSDRBlog Dongle v3 is not suitable for Bias Tee switching without probing/soldering its interiors separately.
(Sorry for the noob question(s), I'm just trying to play it safe before I try out anything silly.)
All help is kindly appreciated. Thanks.