Advice on raising antenna


I am asking for some advise on raising my antenna.

I have the version 10 FlightFeeder with a 5M antenna cable which I thought was long enough.

My problem is that I needed to have my antenna higher to clear a ridge to the north of my position. The 5m cable is stretched to it full length but after getting enough nerve to climb a ladder on top of the roof it looks about 3m to 4m low.

I have read where extending the antenna to get it above interference is acceptable but may cause a loss of data because of the extended cable. Would another 5M cause much of a problem? And also could a higher grade cable be used to overcome this if it is a problem?

Thanks in advance for any advice.


10 meters of low-loss coax shouldn’t be a problem. Instead of adding an additional 5 meters and connecting them together half way I would replace the entire coax with a 10 meter length of LMR240 with a male N connector on one end and a male SMA connector on the other. That way you won’t have to worry about the midway connection coming loose or allowing water to enter the cable.


I agree that I’d replace the entire run rather than join but I’d suggest LMR400 or Hyperflex/Ultraflex 10, depending on what’s available where you are.


Hi HarryHumphrey, To make your effort worthwhile, that antenna really needs to be well above any solid obstruction so that it has a good clear line of sight to the horizon, if that were possible from your location?

I have a line of houses 150 mtrs away and their front door steps are above my roof line, clearly depleting what my antenna can"see"in that direction, there’s no way I can get my antenna above there roof line, so I just make do, but so long as traffic is high enough.
ive got over 200 miles NNW, but pushing it at about 80 miles SSE unless their high enough (aircraft)

Thank you for the replies which are a great help in making the decision to go ahead with raising the antenna.

I can get LL400 cable keithma, which I think is the same as LMR400. Is this correct? Also are the plugs on the original cable a N Male to the antenna and a SMA Male to the FlightFeeder. I would hate to order the wrong ones. As you can tell I am new to this.

Thanks again for all your help.

I suggested LMR240 over 400 even though LMR400 has much less loss because 240 is much lighter weight, fairly thin and easier to work with. LMR400 is thick, stiff and heavy. It’s like trying to uncoil and straighten out a garden hosepipe in freezing weather. Also because I remember that once upon a time the web page about FlightFeeders said they came with LMR240 so I thought that’s probably what he already had.

I think LL400 is the same as LMR240 but compare the technical specifications of the two to be sure, especially the loss per 100 feet or meters at 1GHz.

Thanks for the info.

The FlightFeeder came with RF100 cable so I guess that the LMR240 is much better by the sound of it as the RF100 is fairly light. I will check with the supplier that the LL400 is the same as LMR400 before I order.

Attenuation for 10m cable at 900 Mhz:
LMR400 = 1.28 dB, Avg Power = 580 W
LMR240 = 2.48 dB, Avg Power = 260 W

(1) The difference in attenuation is trivial.

(2) This is NOT transmitting senario handling tens or hundreds of watts. This is receiving scenario handling fraction of a Watt.

(3) LMR400 is stiffer and harder to handle compared to LMR240.




Thanks for the comparison of the 200 and the 400 cables.

The supplier who I deal with only has 195 and 400 cable premade so I take it

I should go with the 400 to be on the safe side.

This is like using a cannon to kill a fly :wink: :slightly_smiling_face:

LMR195 is good enough for 10 meter long coax ONLY IF you install a LNA near antenna
10m LMR195 Attenuation @ 900mhz = 3.65 dB


Exactly. With such weak signals, any attenuation/loss is important.

LL400 looks to be an equivalent of LMR400.

I use LMR195 (10 meter length) and have been very happy with it. The LMR400 I tried was too difficult to route. There is little difference between LMR195 and LMR240.

the “ultraflex” version of LMR400 is much easier to deal with in terms of routing and bending

This is a FlightFeeder so it isn’t an option to use the usual filtered LNAs, as you would lose the GPS signal.
Good quality co-ax is really the only option.

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Oh, I have missed the point that OP has Flightfeeder.
Thanks for reminding.

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O.K. This is getting confusing as there seems to be a lot to learn. As I have a FlightFeeder is it fine to use either the LMR195 or the LMR400? and as there is not a great difference in price between them I would go for the cannon approach. Also, my run is fairly straight. What is a LNA? If I can,t use the LMR’s what should I be using.
Thanks for all your help.

As 10 meter of LMR195 has about 4 dB attenuation, a LNA near antenna is required to keep noise floor low. With a Raspberry Pi feeder this can be done. However as Flightfeeder uses a GPS antenna as well, this cannot be done with Flightfeeder.

Coclusion: For Flightfeeder rule out LMR195 if it is 10m or longer. Use LMR240 or LMR400.


LNA = Low Noise Amplifier
It amplifies the RF signals received by the antenna to compensate the signal attenuation by long coax.


Thanks abcd567 for the explanation.


Your decision to use cannon aproach (LMR400) is right. :+1:

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