Micro Motor Community

REALLY lightweight dipole! Ultralight antenna


#1

Guess which one weighs less!
It saves about half a gram, range appears to still be good.

For wire length in mm:
149987mm * (magic radio velocity in your specific wire number, 0.96 to 0.98 generally) / frequency in MHz.
In my case I’m using R band #2, 5695mhz, so:
149987 * 0.97 (I’ve no idea, so I split the difference) = 145487.39 (be pedantic when sizing antennae), / 5695 gives us a wire length of 25.546mm. That’s lovely for a half wave dipole, do note that this is the total wire length (or length for a monopole). We’re making a dipole do hack that in half, for 12.7ish mm.
Cut two of those, one goes on ground, one goes on signal. Presto!

You want them aimed as exactly away from each other as possible, and soldered to points as close to each other as possible.

I’ve read that some VTX units use their cloverleaf as a heatsink and fry without it, so be aware of that.
A classic sleeve dipole (or whatever they’re called) doesn’t make as good a heatsink, but it’s probably still better than one of these, so check your VTX temp from time to time. Odds are if you’re racing around with it it’ll be fine, plus a whoop doesn’t exactly spend a lot of time powered on all at once anyway.
If you do cook one, let us know!

Bonus: You won’t rip the antenna off as often if you flip it over like I did in the picture above.


Any tips for improving video range?
Best Brushed Quad Parts as of March 2017?
Vaccuum forming Tin¥ ₩hoop canopies
#2

I like that and it really gets me thinking. I wonder what you could do with an inverted v, or maybe even a 5/8 wavelength dipole instead of a 1/4. I’ve always wondered about the inherent nature of a true dipole to be 75 ohms and not matched to our transmit impedance of 50 ohms. I know closing the angle from 180 degrees down to about 120 brings the impedance of the dipole closer to 50 but also distorts it’s radiation pattern in sort of a directional way. 5/8 wavelength gives about 3 dbi more gain - and a 120 degree inverted v should bring swr down while focusing the radiation pattern slightly more below the craft than above with your configuration. Could even make the fennel zones harder for the receiver to “see” since they’re aimed down a bit now…


#3

Nice job Bob. The regular dipole should have greater range than the original “folded dipole” - provided the antenna tips are not aimed at the receiver. The strongest signal is perpendicular to the wire; the weakest is out of the tip. What kind of antenna is on your receiver?

NotFastEnuf, the v-type dipole should work well too. It trades a small amount of gain for a slightly wider radiation pattern. Cool.

Thanks,

Paul


#4

Have you tested range before and after?


#5

It has a 4 leaf rh circular thing and a directional flat-panel-4-node-stacked-like-a-yagi thing. Generally the panel wins.

I’ll see about doing some specific range testing tonight, now that I have three of these cameras (oops?) it’s more practical than it was before.
It stays pretty good through three walls and 70’, which is a good start!


#6

@Bobnova
I really like how you laid down the dipole on the left camera -
Where does the antenna end up in relation to the frame/build?
Does laying it down like that affect your reception at all?

BTW - really nice job on the right, too


#7

That is really trick! A lot of very-high-powered organizations in
competition motorsport have spent a ton trying for a 2% weight loss with
no trade-offs. Good Job Bob!!


#8

Range on the laid down antenna seemed maybe down a little bit indoors, but not much. Haven’t tried long range outside yet.

It ends up just above the FC, insulation is important there.


#9

The eachine replacement cam for the qx70 I believe is the same style. I just did mine the other day too. Removed a cp Cloverleaf and soldered the dipole inverted. Believe it or not, it gives a better picture than the stock makerfire camera that has the dipole on the top. Probably nothing to do with orientation but more in how short I kept the radiating point where the active element is soldered and good measuring on the dipole itself. Who knows really - may just be a difference in qc between two production batches.


#10

Update:
You can cut the top of the tab off the vtx too.


Don’t cut the bottom of the solder pad for the antenna signal off. If you look at the from side of the vtx you can see where the trace comes through the board and goes down to an inductor. If you cut too far and can’t solder to that trace (or destroy the inductor) it’s over.

Really really really REALLY don’t breath the dust, it’s lead (kill brain cells permanently), fiberglass (stays in lungs forever), solder resin/flux (acidic), and fiberglass resin (no clue, but I’ll bet it’s toxic!)

Don’t be in line with the cutoff wheel if you use one, either. They randomly explode.
Wear eye protection.
Maybe just don’t cut it off.


#11

@Bobnova are they the same diameter wire?

Edit: Or are they just two different wires/colors?


#12

Not up to speed on my antenna theory as much as I should be but does the space in between the solder pads also contribute to the tuned length?


#13

@Kamsleo69 they’re different wire, just whatever I picked up first. If I recall correctly they matched originally but I dropped one while soldering and didn’t find it.
They should probably be identical.

@NotFastEnuf I’m not sure, I was contemplating that this morning actually. Electrically it seems like it shouldn’t, but from an electromagnetic wave shaping standpoint it should.
Bottom line: I don’t know, find an amateur radio person and ask. They might not know either though as they’re typically dealing with metres of antenna so an inch or two gap doesn’t matter as much as a 2mm gap in a 25mm antenna.


#14

When I try this (soonish)
I will plan on cutting long, and shaving down till I get the good reception.
Obviously I will have to make two sets so when I cut too short I’ll know the right length for the permanent set😋


#15

Perfect! Let us know what you end up with.


#16

Really awesome idea @Bobnova! I’ll have to try this on the Nifty. It’ll keep the weight and the profile low. What I was thinking in terms of the gap is that you can solder the wire to the tabs with a bit protruding toward the other but stop short of touching eachother. Then just add a tiny drop of hot glue (or epoxy or something if it’s too hot for hot glue) there to prevent any shorts.


#17

That might work, might not. The point where the signal goes into the antenna wire actually makes a pretty big difference, it may not like having a little tab sticking out on the other side of the feed point.


#18

Good point. Once I have some goggles I’ll have to try it and see if it works or not.


#19

I was working on an old eachine lt200 vtx to change out the antenna fitting and noticed on that one there is almost a quarter inch of bare trace on the signal wire before it gets to the fitting. That’s gotta be throwing off the tune of the antenna. I may do the @Bobnova trick where I grind it all off. Or maybe just update (better for my health).

Edit: come to think of it, I’ve put it through heck breaking antennas off on large brushless quads - maybe that’s also the reason it never cooked waiting for me to find the wreckage. Haha


#20

Here’s another interesting antenna:

By the way, unless I’m very much mistaken any dipole should be orientated vertically,as along the axis of the dipole the signal is the weakest.
Imagine a doughnut…

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