Bias-t & LNA
- Thread starter Pape
- Start date
Ubbe
Member
As I understand those pictures show the signal using one SDR dongle connected to the antenna coax and you already have the J-pole installed and only want to expand to three dongles and a LNA to compensate for the extra splitter loss.
Your pictures doesn't show any signal strength values and what scale that are used.
But anyhow then it is, as you mention, to just install the LNA at the antenna and see to that the splitter has power pass from one or all outputs to the input. You can enable bias-T power from all dongles to support each other and take the load off one single dongle. The LNA are probably a 20-25dB gain one so you will need to attenuate the signal going into the splitter. Having a LNA at the antenna and then a splitter at the other end of the coax will load the coax with a constant impedance and minimize losses.
A J-pole works fine for amateur radio HAM use as it only needs to cover a 1-2MHz range but if you have tuned the antenna to 156MHz it will probably work fine. It is a very high impedance at the top of the antenna and will be very sensitive to any objects that are too close, even wooden ones. The coax needs to be decoupled from the antenna in some way or the coax will interfere with the antennas functionality.
It's much easier to get a 1/4 GP antenna to work properly as it's installation and use aren't as critical.
If you really need to improve signal levels then a Diamond F23 are three 5/8 elements stacked with a 7dB gain and comes with a cut chart that allows you to cut it to the center of your frequency range, 156MHz.
/Ubbe
are u saying i should enable bias tee on all 3 dongles to power a lna because from what i have read u just need one dongle with bias tee powered and it going to the splitter that has a power pass .
Ubbe
Member
You only need one bias-t if the LNA are low powered. But any extra current draw from a SDR will add to the heat it generates, so better to spread the load, if all connectors on the splitter do power pass.
/Ubbe
Not familiar with that one. You would need two of that type to make a bypass switch, otherwise known as a transfer switch. I’ve picked up a number of similar switches on eBay in the $20-$25 range that were good to 18GHz and had two simple solder tabs for the coil.
