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Old Yesterday, 06:18 AM
Registered User
Croatia, City of Zagreb, Zagreb
Joined Aug 2013
45 Posts
Hi all

Last weekend as weather was awful (hazy) I decided to make some ground test with helix antenna (you can see it on page 106).
Achived range was 3.3km.Due to ground test it was impossible to make test "lineary" because of trees and other vegetation.
Test from 4,5km was unsuccessful but FrSky 2,4GHz (microstrip ant from Flytron) and 433MHz telemetry (Yagi 4 elements) was still operable.We suspect on limited LOS.
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I need to say according to Jcoppens calculator my antenna actualy have 2 3/4 turns because I didn't count 1/4 impedance match turn. Also I don't have SWR meter so antenna is not tuned.

Now I plan to make new one (jcoppens calc) with 6 turns but I am little confuse from wich point to measure winding space from reflector (after that I read so many post from this threead).

According to jcoppens calc I normaly start to count wind after first 1/4 turn (matching wind).
So for 5,8GHz gap is 0,4mm.Winding step is 11,8mm.
I make template on paper for better understanding/explanation.
First turn is acctualy 12.2mm because I need to include 0,4mm gap.Every other is 11,8mm corresponding to calculator.
Is that OK or????
Is OK to use plywood (2mm) for support or polycarbonate also 2mm.
Please advice.
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Thanks
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Old Yesterday, 06:55 AM
surf monkey
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United States, CA, San Diego
Joined Aug 2011
1,217 Posts
Quote:
Originally Posted by KresoZG View Post
I need to say according to Jcoppens calculator my antenna actualy have 2 3/4 turns because I didn't count 1/4 impedance match turn.
wait, what? is this correct? Do we really need to subtract that first quarter turn? I was counting my '4 turn' from the point the coax feed line was connecting to the helix/the outer shield connecting to the ground plane, until the end of the corkscrew.

So does that mean that I really have a 3.75 turn antenna??? From where are you supposed to start counting? from the start, center, or end of the 'wave trap' strip???
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Old Yesterday, 09:34 AM
Registered User
Croatia, City of Zagreb, Zagreb
Joined Aug 2013
45 Posts
Quote:
Originally Posted by changosurf View Post
wait, what? is this correct? Do we really need to subtract that first quarter turn? I was counting my '4 turn' from the point the coax feed line was connecting to the helix/the outer shield connecting to the ground plane, until the end of the corkscrew.

So does that mean that I really have a 3.75 turn antenna??? From where are you supposed to start counting? from the start, center, or end of the 'wave trap' strip???
If You ask me I am not sure. I also wait for someone expert to confirm.
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Old Yesterday, 04:23 PM
Wallop!
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Bussum, Netherlands
Joined Oct 2009
785 Posts
You are right, the first quarter turn doesn't count if you're using it as a impedance transformer like JCoppens. But the effect will be negligible anyway. You're over thinking it although 3 turns is the minimum to get circular polarisation. To be on the safe side you better use 3.5 or 4 turns.

I'm not an expert btw, just a fan of John
Martin
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Old Yesterday, 05:17 PM
Wait...what?
gbmarsh's Avatar
Canada, BC, Abbotsford
Joined Sep 2010
1,191 Posts
Quote:
Originally Posted by Martin7182 View Post
You are right, the first quarter turn doesn't count if you're using it as a impedance transformer like JCoppens. But the effect will be negligible anyway. You're over thinking it although 3 turns is the minimum to get circular polarisation. To be on the safe side you better use 3.5 or 4 turns.

I'm not an expert btw, just a fan of John
Martin
Yep, this is correct, it's really not that critical IMHO. I have tested 2 antenna in the air, 1x 3 turn with the quarter turn match and 1x 3.5 with the quarter turn match. I turned back at just over 3km due to some small break ups in the video that could have been local interference but the image quality was great from both.

Here is a video from the 3 turn with the little break up at 3km. I turned back because this was the goal for this flight but I think I could have flown through that bad patch and gone further.
Bixler 2 FPV 3km Run (13 min 5 sec)


Cheers,
Geoff
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Old Yesterday, 05:22 PM
surf monkey
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United States, CA, San Diego
Joined Aug 2011
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so, is the 'wave trap' also considered a 'quarter turn match'?

I have some left over wound copper wire from when I built my 4-turn (3.75-turn?) that I ended up cutting off since I decided to go with only 4 turns. So, now I'd like to extend my 'wooden cross' support and solder the missing coppper helix section back on.

Should it be OK to re-attach the remaining turns to my existing helix? (I know it was asked before, but I wasn't sure if the losses would be significant or negligible).
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Old Yesterday, 05:29 PM
Wait...what?
gbmarsh's Avatar
Canada, BC, Abbotsford
Joined Sep 2010
1,191 Posts
Quote:
Originally Posted by changosurf View Post
so, is the 'wave trap' also considered a 'quarter turn match'?

I have some left over wound copper wire from when I built my 4-turn (3.75-turn?) that I ended up cutting off since I decided to go with only 4 turns. So, now I'd like to extend my 'wooden cross' support and solder the missing coppper helix section back on.

Should it be OK to re-attach the remaining turns to my existing helix? (I know it was asked before, but I wasn't sure if the losses would be significant or negligible).
I am also 'no expert' but I think it might be tricky to get the 2 sections lined up perfectly and you are probably better off making a new one. Having said that, I'm sure it would still work to some extent and might be worth a try just for the fun of it

Cheers,
Geoff
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Old Yesterday, 11:07 PM
Flying Zayin
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China, Guangdong, Guangzhou
Joined May 2012
964 Posts
Antenna calculators usually suggest minimal reflector sizes, but what about the maximals? I.e., in my case the reflector should be at least something between 19 and 20 cm diameter. Question is, what if it is much bigger? And how much bigger will be too big? Say if I have 20 by 20 cm square copper plate it is probably OK as it is quite close to minimal diameter. What if I have 40 by 40 instead, or (just for example of course, not for real life) 2 m by 2 m?

Is it 'the bigger the better' situation or does it still have some 'within reason' limitations?

And what if one side is longer than another (rectangle but not square, or oval rather than round)?

Thank you.
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Old Yesterday, 11:26 PM
surf monkey
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United States, CA, San Diego
Joined Aug 2011
1,217 Posts
Quote:
Originally Posted by Cathay Stray View Post
Antenna calculators usually suggest minimal reflector sizes, but what about the maximals? ... Question is, what if it is much bigger? And how much bigger will be too big?
Is it 'the bigger the better' situation or does it still have some 'within reason' limitations?

And what if one side is longer than another (rectangle but not square, or oval rather than round)?

Thank you.
I have the same question...

more generally, how does increasing the reflector size past the recommended dimensions affect its gain & performance? Does it have a negative, positive, or little to no effect?
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