Strange problem with my FA antenna installation


#1

Hi all.
I have a strange situation happening with my antenna.
I have the FA antenna mounted on the roof top. In the beggining i tried mounting it on a metallic post (at the very end of course).
I noticed that most of the times the performance was very poor and it actually varied a lot during the day. (from 60-80 messages /sec up to 250 messagesfor the same number of flights).

I tried to investigate what the issue is and realized that whenever i dismounted the mast from the wall and hold it in my hands, the messages/sec as well as the number of flights skyrocketed. It went from 30 flights with 80 messages/sec to around 65 flights and more than 1000 messages.

Every time i mount the mast on the wall the opposite happens. Poor performance once again.
My next step was to mount it on a PVC pipe, just to see the results. Now i’m able to go as high as 700 messages but with the same behaviour. whenever i dismount the pipe from the wall i get much more results.
The cable in case you are wondering is RG58 (about 15 feet) and there is no kind of interference in the proximity.

Thanks


#2

How are you clamping the antenna to the mast? Photo maybe


#3

With the regular clamps that came with the antenna.


#4

I think it might have to do with the antenna itself.
Whenever i push the connector of the antenna, i get a better signal. Does anyone had a faulty antenna before?


#5

I hope you’re not mixing 50 Ohm and 75 Ohm N-connectors because the thickness of the inner pin is somewhat different, better check if the center piece of the N-connector on the antenna is not bended or split open.


#6

Good idea.
The conectors i use are 50 ohms as well but i will take a look in case the pin is bended.

Edit: I checked the antenna connector and it looks fine.
I’m facing a dead end here.


#7

I too have noticed this anomaly with the FA 26" antenna.

In my case the antenna is mounted using the supplied clamp to a 6m aluminium mast. In turn the mast is secured to the rear of my galvanised steel garage by using a two metre length of wood between mast and garage. The bottom of the mast is resting on the concrete base.

I have the dongle outside housed in a plastic bag 3m under the antenna connected using LMR400 cable, N connectors and a reducing N to SMA adapter and have had this for a long time now but only recently with the FA antenna. Before that I was using an antenna supplied for a FR24 receiver which had since been returned (I got to keep the antenna for awhile!).

If I raise the mast off the concrete base I get a major drop in performance, it only has to go up a metre before this happens.

At first I thought it might be grounding causing the problem but an earth cable between the raised mast and my earthing rod did not improve the performance.

So my issue seems to be that the higher I go off the ground, the worse the performance. I don’t like compromising in this particular case.

I do wonder if it an antenna design problem in cases where the antenna is located above a steel object such as my expansive garage (100 sq ft). Whether the influences of the steel roof appear to behave like a ground plane? Don’t know.


#8

Antennas can be very sensitive to small changes in the near field - in some cases we found that shifting the mounting bracket by a few mm could cause large changes in reception.
The closer to the antenna, the more likely it is to have an effect.


#9

The problem is that whenever i twist it and leave it there i get completetely different performance.
Should the FA antenna be mounted on a plastic or metallic mast?


#10

The way it’s constructed, it should not matter, it has a lambda/4 ground decoupling sleeve on the bottom part.
I have it on a metallic mast.

PS: This model was posted on the antenna thread:


#11

Problem solved.
As it turned out all kinds of cable that i used were somehow picking up interference. I changed it to LMR-400 and now everything is running smooth.


#12

I moved the Prostick Plus indoors with a full length of LMR-400 and it performs much better.