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Apr 14, 2011, 06:50 PM
Engineer for Christ
IBCrazy's Avatar
Thread OP
Quote:
Originally Posted by Flightbox
Whats everybody using to check SWR on the home brew antennas. Is there a inexpensive meter out there to get set up with. Maybe a little you tube tutorial on setting the SWR would be great for all us that struggle with this kinda thing, Just a thought. Dave
There is no cheap SWR meter for this stuff. Thus you would be stuck buying one that costs around $300. And building your own? Don't even try. It is way more difficult than you think.

But why bother? Really. If you follow the tutorials and make your antennas very accurately there is no need to test for SWR. The SWR is as good as your construction. I use mine mainly for verification and to fine tune helicals, but that's about it.

-Alex
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Apr 14, 2011, 06:53 PM
Registered User
Quote:
Originally Posted by IBCrazy
I make all of mine to resonate at 2439MHz. This is dead center of the 2.4GHz band. SWR goes as high as 1.3 from the bottom (2360MHz) to 10 at 2439, to 1.3 at 2510MHz.

No need to make individual units. The difference between 1 and 1.3 SWR is hardly noticable.

-Alex
Using my VTX, the lowest channel is 2370MHz, and the highest 2510MHz. I've had a bit of a read up on SWR but I still don't fully understand it. What sort of range difference would it make with 2x cloverleafs on one of these frequencies (which you say has a 1.3SWR) to your optimal frequency (SWR of 10 at 2439MHz)?

I normally try to use 2370 or 2510 just to stay out of the normal household 2.4GHz ranges and get less interference.
Apr 14, 2011, 07:23 PM
Dax
Dax
There is no spoon
Dax's Avatar
Quote:
Originally Posted by IBCrazy
And building your own? Don't even try. It is way more difficult than you think.

-Alex
Hey now, that's not a very HAM attitude! Building your own gear is half the fun, using the gear afterwords is just a bonus.

Edit: The one in my first link is dead simple, and works on Tx's up to 1 watt, which is perfect for the power levels we are working with.
Apr 15, 2011, 12:05 AM
Registered User
IBCrazy, I just built a pair of cloverleaf antennas. Mine are perfect by no means, actually they are very off. But they work very well! Just from bench testing I saw a huge difference between the stock antennas and two cloverleafs. No matter what orientation the plane was in reception was clear.

I can't wait to get out and do some range testing!!
Apr 15, 2011, 12:31 AM
FPV Pilot
ttucker's Avatar
Quote:
Originally Posted by mitsudriver274
IBCrazy, I just built a pair of cloverleaf antennas. Mine are perfect by no means, actually they are very off. But they work very well! Just from bench testing I saw a huge difference between the stock antennas and two cloverleafs. No matter what orientation the plane was in reception was clear.

I can't wait to get out and do some range testing!!
mitsudriver274, are you using 200mw 5.8GHz? One cloverleaf on the transmitter and another on the receiver?
Apr 15, 2011, 12:38 AM
FPV junkie
m_beeson's Avatar
Alex,

I have a couple of questions for ya.

1) Your Blue Beam antennas, are they clover leaf? I noticed that the transmitter has three lobes and the reciever has 4 lobes. I have missed the details on these (not for a lack of reading), could you expound?

2) also reguarding the 1280MHz 9.5dbic helical:
does it work well with the Blue Beam? and do you have any test results, and possible video of this antenna in action?

Mike
Apr 15, 2011, 07:48 AM
Engineer for Christ
IBCrazy's Avatar
Thread OP
The BluBeams are 1 skew-wheel and 1 cloverleaf antenna. Nothing special about them.

They are compatible with the helical as they are all RHCP.

I have no video of it in action. Why? I simply can't use that much gain. The video would have a range of 9-10 miles, but my transmitter is limited to 2-3 miles. I have not had time to finish my LRS system to push that limit, nor do I have an airframe capable of those distances yet.

Here's a video using the BluBeam system. I was running out of TX range and had plenty of video... on OMNIS!

(3 min 28 sec)


-Alex
Apr 15, 2011, 10:39 AM
FPV junkie
m_beeson's Avatar
Alex,

I saw that video. Impressive.
Apr 15, 2011, 10:41 AM
FPV junkie
m_beeson's Avatar
Quote:
Originally Posted by IBCrazy
The BluBeams are 1 skew-wheel and 1 cloverleaf antenna. -Alex
is that the best combo that you have discovered yet?

as apposed to using two clover leaf, or two skewed planars?
Apr 15, 2011, 11:06 AM
Registered User
I do think this stuff all depends on where you are flying. I fly in an environment where I seem to be picking up lots of interference (created a thread on it). I went with CP omnis on the ground and on the plane and it helped but definitely didn't me to where I need to be video-wise to fly in that environment. So I switched the ground to higher dbi linear antennas (a biquad and a patch on diversity) and tried both the Cloverleaf and the Skew Planar Wheel on the plane and it was much much better. I haven't yet pushed out more than about 1,500 feet LOS yet and I'm sure my set up is super inefficient but it works.

That said, my wing broke last weekend pulling up from a dive so spent this last week rebuilding. I should be ready to go again by tomorrow for some more FPV fun, but plan on switching the linear ground unit(s) to a cp helical which I believe should be the magic combo for good clear video and distance.
Apr 15, 2011, 11:08 AM
Registered User
Quote:
Originally Posted by Flightbox
Whats everybody using to check SWR on the home brew antennas. Is there a inexpensive meter out there to get set up with. Maybe a little you tube tutorial on setting the SWR would be great for all us that struggle with this kinda thing, Just a thought. Dave
This meter will cover most of what many people are using, 900MHz upto 2.5GHz.

http://www.theantennafarm.com/catalo...oducts_id=4378

IBCrazy uses one himself I believe.

Response to Bandwidth could be questionable cause thats pretty wide but it will be good enough to give you comparative tests. I wouldn't rely too heavily on the absolute readings but it should be fairly close.

And reasonably priced,
There are more expensive units such as BIRD brand but they don't have as much bandwidth and you would need to buy additional Plug in Elements to change the frequency band to be measured but they are much more accurate. Professional grade.
http://www.bird-technologies.com/

A dummy load is useful when testing transmitters as well.
Last edited by garris2; Apr 17, 2011 at 09:39 AM. Reason: Correct link added
Apr 15, 2011, 12:06 PM
Registered User
Quote:
Originally Posted by stergiopilus
I've had a bit of a read up on SWR but I still don't fully understand it.
SWR, or VSWR is the Voltage Standing Wave Ratio.

Example: Power from transmitter into antenna.

It is an indication (Ratio, so there are no units) of the amount of Power being delivered from a Transmitter into an Antenna, COMPARED, to the amount of power being reflected back from the Antenna. Electrically speaking, not externally. ie, efficiency.

What we want is ALL of the power from the transmitter going into the antenna and none of it coming back. This is ideal, but there are always losses.
100% power transfer would be a ratio of 1:1
Something less than 100% might be 1:1.1(very good), 1:1.3(pretty good), 1:1.5(good), 1:10(bad) eg. etc.

The bad thing about having power reflected back is that a) it's not efficient, and b) the reflected power goes back into your Transmitter and helps to over heat it.

To get maximum power transfer you need to have good impedance matching of your transmission line (coax).
This means not too many connectors, each change on transmission line size there will be a slight impedance mismatch. The transmission line changes size as it goes through the connector even if you are using the same size coax on the other side.


Impedance is a little bit like resistance but different.

Impedance is resistance at frequency, as frequency changes the resistance changes.

In our case the characteristic impedance of the coax over a given designed frequency bandwidth will look like 50 ohms.

Resistance is, well resistance at DC.
(This is very generally speaking for the layman so don't flame me).

http://en.wikipedia.org/wiki/Impedance_matching

The other important point as IBCrazy mentions, is having a tuned antenna, that is, an antenna that is tuned to your frequency of choice.
Tuning is matching the length of the antenna element(s) to the wave length (or part, 1/4, 1/2, 1/8, full) of the frequency.

This will help the Current wave to travel through the antenna in the correct phase with the voltage wave ensuring minimum reflections.

In the attached diagram, current is at a maximum where the feed line meets the antenna and minimum at the tip.
The voltage is minimum where the feed line meets the antenna and maximum at the tip.

This will occur where the antenna element is the correct length for the resonant frequency, the impedance of the antenna will be at a minimum and this will allow maximum power transfer into and radiated from the antenna.

http://www.google.com.au/url?q=http:...ed=0CBwQygQwAA

cheers
Geoff
Last edited by garris2; Apr 15, 2011 at 12:11 PM.
Apr 15, 2011, 06:29 PM
TBS Crossfire or DragonLink?
Hello Alex,

we know you can get out to 2-3miles on your BlueBeam antenna's on 1.3ghz VidTx and VidRx.....


can you use your 5.8ghz and put CloverLeaf on VidTx and Skewer Planar Wheel on your VidRx ?

I want to see how far you can get without the dreaded Rf noise with using 5.8ghz VidTx/VidRx.....and after that, you got us sold
Apr 15, 2011, 08:39 PM
Engineer for Christ
IBCrazy's Avatar
Thread OP
Quote:
Originally Posted by LexusFPV
Hello Alex,

we know you can get out to 2-3miles on your BlueBeam antenna's on 1.3ghz VidTx and VidRx.....


can you use your 5.8ghz and put CloverLeaf on VidTx and Skewer Planar Wheel on your VidRx ?

I want to see how far you can get without the dreaded Rf noise with using 5.8ghz VidTx/VidRx.....and after that, you got us sold
I don't have 5.8GHz... yet. Markus just sent me his custom VTX, though. We'll see how far I can go. Probably beyond my 72MHz RC range
Apr 15, 2011, 08:41 PM
Engineer for Christ
IBCrazy's Avatar
Thread OP
Quote:
Originally Posted by garris2
This meter will cover most of what many people are using, 900MHz upto 2.5GHz.

http://www.aesham.com/display_pages/cn801.shtml

IBCrazy uses one himself I believe.

Response to Bandwidth could be questionable cause thats pretty wide but it will be good enough to give you comparative tests. I wouldn't rely too heavily on the absolute readings but it should be fairly close.

And reasonably priced,
There are more expensive units such as BIRD brand but they don't have as much bandwidth and you would need to buy additional Plug in Elements to change the frequency band to be measured but they are much more accurate. Professional grade.
http://www.bird-technologies.com/

A dummy load is useful when testing transmitters as well.
I own a Daiwa SII. Great meter, but stinks at reading SWR accurately. Just try to keep the reflected meter pinned at 0.


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