Need an advice for an Signal, Power,...  Splitter. - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: November 21, 2020, 09:15:32 am
content: HiI still need a Splitter to hang many SDR Receiver to my VHF Antenna.I look on ebay for hours and I found an interesting candidate.https://www.ebay.de/itm/PROFESSIONAL-SPLITTER-AMPLIFIER-20-200MHz-7-1981/184382555709Here a Picture from inside:https://i.ebayimg.com/images/g/qKEAAOSw~51fI2-I/s-l1600.jpgThe look beefy!If I just need 12V for the internal Amp (who is nice to) that sound very good to me.So could that be a good deal?I just need to put as many SDR as Possible to my VHF Antenna for the Various Signals the receive at the same Time.Thanks

author: radiolistener
author_rank: Super Contributor
timestamp: November 21, 2020, 11:13:21 am
content: There is no way to split signal with no power loss and no raise noise level.So, the best way is to use mechanical relay to connect antenna to the input which you're using at the moment.But these relay needs to be properly designed for RF.

author: radiolistener
author_rank: Super Contributor
timestamp: November 21, 2020, 11:32:45 am
content: Quote from: Lord of nothing on November 21, 2020, 09:15:32 amif you want to split antenna between two receiver for a wide bandwidth, you can use 6-10 dB LNA and resistive splitter.For example lna:https://www.aliexpress.com/item/33042467693.htmlResistive splitter:https://www.aliexpress.com/item/4000152357421.htmlNote, that 1-2 splitter needs resistors R = Z0 / 3, for 50 Ohm it needs to be R = 50 / 3 = 16.7 Ohm. These Chinese splitters often use 51 Ohms resistors, so you will need to replace it.Resistive splitter has about 6 dB loss.You can also try this splitter:https://www.aliexpress.com/item/32922534818.html

author: Lord of nothing
author_rank: Super Contributor
timestamp: November 21, 2020, 12:46:19 pm
content: I need to split the signal into as much as possible SDR since my VHF Antenna is very good and I need to receive as many signal as possible. I have a List (in my Head) what I want to 24/7 decode for security reason.The box what I post have an internal LNA build in. So the signal should be put out with the same strength as the come in.

author: radiolistener
author_rank: Super Contributor
timestamp: November 21, 2020, 07:56:00 pm
content: Quote from: Lord of nothing on November 21, 2020, 12:46:19 pmin such case you're needs single direct antenna ADC with many DDC receivers implemented in digital domain.If you split antenna signal you will lose signal power. Each splitting leads more signal loses. If you have many splits, you will have very high signal loss and all receivers will work very bad.Quote from: Lord of nothing on November 21, 2020, 12:46:19 pmLNA adding noise and non linear distortions. It will limit dynamic range.You can split it in such way, but you may lose dynamic range and sensitivity.Also receivers will affect each other, so you will have additional noises from other receivers connected to LNA output

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 21, 2020, 09:31:48 pm
content: i think splitting can be done after LNA buffering. after splitting can be gained by LNA again on and on... i believe thats what the OP showed. noise? well i guess thats the tradeoff between splitting and loss, and the difference between cheap stuff and expensive one.

author: ch_scr
author_rank: Frequent Contributor
timestamp: November 21, 2020, 09:51:14 pm
content: Quote from: Mechatrommer on November 21, 2020, 09:31:48 pmI second that LNA first split second works.Given that i.e. an RTL-SDR is not steller in terms of input sensitivity or input linearity when strong signals are concerned, an LNA would propably even improve sensitivity / noise. And the bar to not ruin linearity with strong signal would also be not that high.But I also second the concern about isolation, specifically with regards to i.e. the RTS-SDR input is not 50 ohms (and splitters having that as a requirement to give isolation)My recommendation would be LNA near the antenna, amplifier where the SDR are and a multi-way coupler (not a splitter - couplers bring isolation). Maybe even an cable TV splitter, given the short cable runs to/from it and the not 50-Ohms-ness of the RTLSDR.When using PLUTOSDR the input is about 50ohms (so splitters would be ok) and sensitivity is good (but if you got a long cable run that brings noise and attenuates your signal - so an LNA might have benefits) but strong signals will still mess it up.I've heard limesdr has a pretty deaf input and would propably benefit from an lna.

author: David Hess
author_rank: Super Contributor
timestamp: November 22, 2020, 04:07:26 pm
content: A good receiver includes an LNA anyway so an external LNA does not necessarily mean that dynamic range is reduced; it depends on the linearity and noise figure of the LNA and not overloading the receiver's LNA. If the receiver includes preselection before its LNA, than an external LNA is likely to suffer from overload under the same operating conditions. Placing the external LNA after spitting will raise the noise figure by signal level lost in splitting but also reduce overload.I suggest first using a splitter without an LNA, and if sensitivity is unacceptable, add an LNA before the splitter. Look for an LNA with a high compression point and high third-order intercept.

author: Lord of nothing
author_rank: Super Contributor
timestamp: November 24, 2020, 08:14:49 pm
content: so i order 2x we will see how it will goes.