1.2-1.3Ghz Tx/Rx All infos on one page - updated: 27/10/2013 - Page 84 - RC Groups
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Mar 20, 2011, 11:42 PM
Registered User
Old Man Mike's Avatar
Since there appears to be an appreciation in this thead of the advantages of circular polarization, here is a CP Biquad design I did which is optimized for multipath rejection:

I took great care to get all measurements within 0.5 mm which resulted in the prototype matching the predicted SWR almost perfectly:

For this design I focused on getting the best axial ratio for a near 10 dBic gain antenna. The result is that the opposite polarized signal is suppressed by aproximately 20 dB over the primary coverage area of the antenna:

Note that this antenna is LHCP. It is easly converted to RHCP by fliping the elements top to bottom.

By the way, the above two plots are quite effective for showing the ratio of LHCP vs RHCP. You can clearly see that the high ratio is maintain over all the main coverage of the antenna in both Az and El.

Additional construction details here:


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Mar 23, 2011, 10:19 PM
Epic Huckin'
paintball_kidz's Avatar
Can some one remove there sunsky 800mw cover off and snap a picture of it? i wanna see if it looks like mine, since mine has problems.

Mar 23, 2011, 10:50 PM
Registered User
There are so many different models/revisions of these.. its crazy.. I have three and they all dont look like yours...
I bought one 2 months ago... that had the wires soldered to the top of the PCB [yours are on the bottom]
I bought 2 a couple of weeks ago, and they had a connector, instead of cables directly soldered on!..

What problems do you have?.. Ill get you a photo of mine when I get to a camera..

Mar 23, 2011, 11:02 PM
Registered User
Daemon's Avatar
Can't see enough detail in your pic to see anything wrong.
Here's what it should look like.

Pretty amazing to consider that people are hand soldering
these SMT components.

Mar 23, 2011, 11:10 PM
Epic Huckin'
paintball_kidz's Avatar
just inability to power on or change channels in the cold. Im doing test right now... at room temperature powers on fine and cycles channels with now power lost. In the fridge and freezer it will not power on. If i plug it in before hand and then put it in the fridge or freezer it will stay on, but as soon as i cycle the channels it shuts off.

zoomed in, do you know what that knob does?

Last edited by paintball_kidz; Mar 23, 2011 at 11:16 PM.
Mar 23, 2011, 11:15 PM
Registered User
Daemon's Avatar
That could be a sign of a bad solder joint or crack in one of the traces
that pulls apart when it's cold. Try gently pushing on or flexing the board
when it's powered but otherwise not working. Generally you'll need a
good magnifying glass or hand held microscope to find cracks.

Mar 23, 2011, 11:21 PM
Epic Huckin'
paintball_kidz's Avatar
it appears that maybe 2 of these parts on mine are touching and yours are not? could that be a problem.
Mar 23, 2011, 11:37 PM
Registered User
Daemon's Avatar
No, those just look like intentional differences in the board/layout design.

Mar 23, 2011, 11:54 PM
Registered User
If it is a crack/bad solder joint.. why not put it on an [old, unused] frying pan/hot plate and try to reflow it??

I have done reflow soldering on a clothes iron, and it works well.. the added benifit is you have a metal case that contains the pcb - which means components cant fall off the bottom.. maybe the vias.. otherwise use a hot air gun [or flame, reaaaly far away from the components] to get at it from the top..
Mar 23, 2011, 11:57 PM
Registered User
Originally Posted by Daemon
No, those just look like intentional differences in the board/layout design.
Yes. They thought 'lets not follow the recommended application schematic and leave out the decoupling cap.', then went ahead and made millions of the PCBs, tested them and said 'oops, it needs that cap!!! I know, lets manually solder it in!'.

Mar 24, 2011, 12:04 AM
Epic Huckin'
paintball_kidz's Avatar
Well it does power when its cold, it just doesnt power on 100% just enough to flicker or barely show the screen light.
Mar 24, 2011, 12:12 AM
Registered User
Hmm i wonder if anyone else is having similar problems.... i might chuck mine in the freezer and see how i go!! What temp approx?
Mar 24, 2011, 12:15 AM
Epic Huckin'
paintball_kidz's Avatar
i have no clue, but its above freezing level for sure lol. i just toss it in there for a few minute untill the metal case is cold
Mar 26, 2011, 10:51 AM
Registered User
I have a breakthrough [i think]..

I didnt have any problems with 1.2ghz and hxt900s on my assassin wing..but things where well spaced..

I just installed FPV on my new mini skywalker.. the camera is know [$11cmos] for interference.. I made a 1280mhz IBCrazy Inverted Vee and stuck it on.. tested the system.. and immediatly saw jittering on the hxt900 pan servo and interference on the vid signal [the camera was making a buzzing noise aswell].


so I play around [all while having my tx on throttle cut].. and move the active element very close to the HK 6ch v2 rx [2cm] ... and my motor starts!!!

So that gets me to the conclusion that the output from the vtx is interfering with the rx and probably messing up the power for the cam.. [i had terrible lines, and still had lines at the best vtx pos]..

Then I though.. the I-Vee is horiz/vert polarized.. so is the rx antenna... why not try a CP on the vtx??

I slap on the skew planar wheel i made before, instead of the Vee and... silence..
No jittering from the hxt900..
Crystal clear picture!

It worked!

Im going to do some range tests today and see how it goes!!

Could you guys who have the same issue with jittering/etc, test a CP ant, to see if you have a similar result??

Edit: I am using a sunsky 800mw tx & rx

Mar 26, 2011, 11:15 AM
recep's Avatar
Originally Posted by recep
Could you please help me about a confusing situation I'm experiencing. I have got two identical fox 800 tx units from bev rc and their receivers. I connect my vee antenna to one tx power it and no image on the googles until I touch the antenna once then the image comes. I connect the vee to the other tx power the system and I have the image without touching the antenna. With stock antennas everything is normal. I tried it with two receivers same thing happens with that tx and vee combination.
any one?

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