Quick LNA question?

Hi there,

I have had a Kuhne LNA 1090 A TM and its BT 271 N Bias Tee purchased way back when I first got into VR in 2008/2009. Apart from a brief stint of just a few hours mounted at the bottom of the antenna where it reduced the number of aircraft my old RadarBox could see by 95%+ (overload possibly?) it has spent the rest of its life in the box!

Now I realise its optimal position is as close to the bottom of the antenna as possible to maximise signal & minimize cable loss etc. but the problem for me is the antenna is mounted at the top of a 16 foot pole at the gable end of a 2 storey house and I’m not getting any younger to be climbing up & down ladders etc.

I use a 7-8m length of Westflex 103 fitted with N-Type connectors from the Watson 1090 Radar Extender antenna which has performed flawlessly for over 10 years directly into the FlightStick/Pi in the loft and was wondering in the interests of making things easier whether it would be OK to connect the Kuhne onto the end of that length of antenna coax inside the loft, putting the Bias Tee inline before using a flylead to connect to the Pi?

Although sub-optimal I was wondering if that 7-8m length of Westflex 103 might have too much of a detrimental effect with the Kuhne positioned at the radio end instead of the antenna end?

It would be so much easier if I could do my testing with everything in the loft rather than climbing ladders, dropping antenna poles and connecting outside the house and all the faff that comes along with that. Plus the risk of me falling off ladders that I really shouldn’t be climbing in the first place! :stuck_out_tongue_winking_eye:

I don’t plan to go down this road just yet as I will need to pluck up the courage to reconfigure the Pi from FlightStick to Airspy but it would be good to have a plan for when the time comes so I’m soliciting opinions from those with the knowledge and/or experience.

I guess if the test is successful then going up those ladders just one last time to properly locate it wouldn’t be that difficult…

Thanks & kind regards,

Westflex 103 has 16.8dB/100m loss, so an 8m length is around ~1.3dB which shouldn’t have too much of an effect. As it’s been up for 10 years or so, the biggest question would be about the condition of the cable and connectors - any water ingress or corrosion would have a much larger effect than putting the LNA at the end of the coax.

That LNA looks to be a decent quality one, and it has quite a high gain so that is possibly why you got problems using it with the Radarbox - an rtl based receiver would also require careful gain setting to avoid overload as well. The airspy is a bit more tolerant of strong signals however.

You don’t really have much to lose from trying it.


Adding an LNA at the antenna may improve your SNR (signal to noise ratio) but it may also increase your overall noise floor without also having a filter. If I was you I’d look at my signal level graph in graphs1090 and compare the signal levels to the noise levels Not all feeder setups benefit from increased signal amplification. With only 8 meters of low-loss coax you probably don’t need one. If everything’s looking OK, “don’t mess with success.”

I have to admit after a hiatus I was surprised that the antenna was still performing well when I pressed it into service 586 days ago. I remember when I installed it I wrapped self-amalgamating tape around the antenna connector and then the mounting pole went completely over the connector to fix into the base of the antenna so shielding it from the worst of the elements.

Yeah I was thinking I should just give it a go and see how it goes…

Thanks & kind regards,

The Kuhne is not only a decent LNA but also has a narrow bandpass filter 1070-1110MHz so hopefully will do a good job at keeping out of band signals at bay.

My overall plan is to use the Airspy which I am led to believe really works best with a LNA unlike my current FlightStick and Pro Stick Plus in waiting that have their own LNA built-in.

Thanks for your replies guys…much appreciated.

Thanks & kind regards,