Extending your 35 mhz antenna

[venquessa]

I found I still got glitches with my stock RP8D1 in various places at maybe 400m.  Nowhere near what I got when my Rx antenna was bunched up round my Rx though!  Thanks to Ian for that.

I have considered extending the antenna by soldering on a connector so I can interchange extensions and try and see.

I think my last round of glitches have other factors however.  The main area I was getting glitches and even sluggish controls had me flying towards power lines (about 300m away from the plane and a few 100 meters below) which run along the side of a mountain.  I was flying in the mountains which are known for their iron rich, slightly radioactive granite.  None of those things help I'm sure, but the ones that I'm curious about are..

a) Having the radio pointed West, straight out in front of you, while the plane is directly behind you heading East.  So I am between the Tx antenna and the plane.
b) Location of my spotter, if he is between the Tx antenna and the plane in addition to me.
c) Angle of the antenna, I'm assuming they are polarised and as my antenna in the plane is horizontal, my Tx antenna should be horizontal also?

paul

[electrotor]

Yes that article would seem to throw a spanner in the works.

I'm not sure that it throws a spanner in the works but it does indicate that it not as straightforward as simply lengthening the antenna.
Along with the increased gain there has to be sufficient receiver selectivity. The antenna picks up everything to a greater or lesser extent but the receiver has to be able to select only the intended signal and reject the others. Increasing the antenna length could potentially increase the strength of the signals the receiver has to reject.
Why is nothing ever simple?

[electrotor]

I found I still got glitches with my stock RP8D1 in various places at maybe 400m.  Nowhere near what I got when my Rx antenna was bunched up round my Rx though!  Thanks to Ian for that.

I have considered extending the antenna by soldering on a connector so I can interchange extensions and try and see.

I think my last round of glitches have other factors however.  The main area I was getting glitches and even sluggish controls had me flying towards power lines (about 300m away from the plane and a few 100 meters below) which run along the side of a mountain.  I was flying in the mountains which are known for their iron rich, slightly radioactive granite.  None of those things help I'm sure, but the ones that I'm curious about are..

a) Having the radio pointed West, straight out in front of you, while the plane is directly behind you heading East.  So I am between the Tx antenna and the plane.
b) Location of my spotter, if he is between the Tx antenna and the plane in addition to me.
c) Angle of the antenna, I'm assuming they are polarised and as my antenna in the plane is horizontal, my Tx antenna should be horizontal also?

paul

One thing you should never do is point the tx aerial at the model. You will get away with it at short range but not at long range. Try it for yourself with the tx aerial collapsed.
The Z axis on the picture is the telescopic aerial. The least amount of RF energy comes off the top of the aerial whilst the most comes off the side.

[Coyote]

Hi Paul, as Electrotor has said, poor performance will be experianced when pointing antenna straight at the plane. The transmitters and receivers antenna are both forms of omni antennas. As shown above you get a void in the middle vertically from antennas orientation. So pointing two antennas point to point kills the range.

Being 35 mhz your spotters proximity has no real detrimental effect but being out the way is always better then slap bang in front.

When i was testing my 2.4ghz patch antenna which 2.4ghz by nature has poor penetration qualities a person stood infront of the antenna withing a few feet ad absolutly no effect on performance. So 35mhz is no worry.

To have true polorization on two omni antennas the two should be in the same orientation as each other. As the planes is horizontal its best to hold radio level with the ground for maximum effectivness

[venquessa]

Would the "toroid" shape have a hole in the bottom too?

ie.  If I was facing away from the plane, Tx antenna pointed slightly down and the plane flying and climb away from me, that would account for my 35Mhz Burmuda triangle on Sunday.

I mean like this... if the forum will obey.


  /   plane antenna
      <- 300m distance
/  Tx antenna

Angle exaggerated due to only using /'s.

Paul

[Coyote]

Yes thats what we are saying, if you were pointing transmitter antenna that way both voids in the pattern would meet giving poor performance :)

[ak47]

The new calculations for 35 mhz in general are quite easy to remember

101cm or 39" for standard length

So a 1/4 wave antenna will be 202cm in length and a 1/2 404cm

Hi Ian - i have just taken the antenna off my JR synth reciever and it was only 980mm long. Gonna replace it with 2020mm but would the original length account for the poor range oi have been getting? Usefull thread by the way!!

Cheers

Ant

[Coyote]

Most of them cut antennas at that length, 101cm tunes it more accuratly for our use, then extendng it double triple etc then increases its range

[ak47]

Just been out and tested 2020mm in the field -


Tx antenna down for range check i actually managed to run out of field  lol   :D :D

Brilliant

Thanks very much - probably wont sleep tonight !  :)

Ant

[HF_ATL]

I've also extended my rx antenna (rp8d1) to 2m. I get >2km range with no glitch at all!

[Coyote]

Nice result, i`d call that a sucess :)

[HF_ATL]

Thanks! However I'm looking for long range flights, so I'm on the market for a UHF system...  ;)

[Coyote]

Then double your antenna to 4m or 8m

[HF_ATL]

I had already tried that (4m only) and I got almost the same range...

[n00b@FPV]

a tip for if you break your great long Antenna, which is very easy. it do sent have to spoil your day. twist the 2 bits together and run some super glue (you should all have some nearby you if you fpv) down the crack, when you get home, open a window and melt off the super glue then solder it properly