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Nov 17, 2010, 09:32 PM
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Avenger GBU-1H's Avatar
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Discussion

900 MHZ antenna comparison using Anritsu S331E


Friends,

Not sure if this has ever been presented before, but I have all these 900 MHZ antennae laying around that I have acquired whilst slowly trying to piece together a decent FPV uplink and downlink system. I have had some moderately good performance with most of them, others not so good.

Obviously, the antenna is one of many factors that will determine how efficient both receive and the transmit paths will operate.

But, how do I know which ones are really better than others?

I have tried different combination's between my ground station and my Range video 500mW 900 Mhz and I have narrowed it down to a few that seem to work better than others.

One way to measure an antenna’s performance and efficiency is to perform a “sweep” on them using an “Anritsu S331E Cable and antenna analyzer” (more on this here: http://www.us.anritsu.com/downloads/...1410-00484.pdf)

So, I have selected 6 models and performed a test on each one:

1. Arc wireless 12.5 dB panel (for my ground station) – this thing is BIG; about 16”x16” and weighs ~4 pounds (no way this is going on a plane).
2. “Small omni” – this was received with my TX&RX package from Range video that I purchase in 1/09.
3. “Small flex omni” -– this was also received with my TX&RX package from Range video that I purchase in 1/09.
4. L-Com 5dB Flex (BIGGER is better, right?)
5. “Tiny omni” I received as part of a 10 mw 900Mhz wireless video package.
6. “DPCAV V antenna” – just recently purchased (http://www.dpcav.com/xcart/product.p...cat=266&page=1)


I set-up the Anritsu S331E to perform a “return loss” sweep. A definition of return loss can be found here: http://en.wikipedia.org/wiki/Return_loss.

It was explained to me in my Anritsu training class that return loss shows the user how efficient an antenna (or transmission path) is in a given bandwidth. The frequency band was set before and after the stated or desired frequency of 910 MHZ (see sweeps). The downward “spike” indicates an antennas prime efficiency tx and rx frequency.




The results were rather surprising and actually explained much of the performance issues I was having.

Results:


Good: DPCAV “V” antenna - 44.23 dB

ARC Wireless Panel - 34.10 dB

Small Omni - 29.10 dB

Tiny Omni - 14.95 dB




Bad: Small flex – 6.99 dB

L-Com – 9.40 dB



Both the L-com and the small Flex were a huge disappointment, especially the small flex. I have seen these advertised on many websites that carry wireless video gear. Just out of curiosity, I increased the sweep band with, and this one actually swept better at 1.2 GHZ and 2.3 GHZ!

Hmmm… did they give me the wrong antenna? Or are they trying to make an antenna that works on all three of the most popular wireless frequencies?

You be the judge. I am not an RF expert, but using this Anritsu gave me an insight to the problems I was having.

I hope to replicate some of the custom antennas I have found here on the forums. Once built, I will publish my findings.

Thanks for your time. I welcome honest & courteous feedback.
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Nov 17, 2010, 10:00 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Great information! I have a couple of requests...

First can you please edit your post and include captions for the pictures stating which antenna they are for? It looks like some of the charts are mixed up in relation to the pictures of the antennas. Therefore, it's hard to tell which antenna is which. Plus I don't know which pictured antenna is "small omni", or "LCOM", etc.

Second, I would love to see data on this antenna as it's the one I'm currently using: http://www.dpcav.com/xcart/product.p...cat=266&page=1

edit: Nevermind, I see captions on the pics now. lol
Nov 17, 2010, 10:39 PM
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Avenger GBU-1H's Avatar
Thread OP
Twinturbostang,

Thanks for your interest. I would like to see the sweep pattern on that one also. Maybe someone could donate one for review? Not sure how long I will be able to keep this Anritsu - just on "loan" for now.

I think if more retailers would post some kind of RF pattern or sweep result with their antenna products, they would get more buyers.

Look on any other website that markets just antennas.
Examples:

http://www.cushcraftamateur.com/cata...11_Catalog.pdf
http://www.telewave.com/pricelist/antfiberdat.html
http://www.kathrein-scala.com/pcs-aws_panel.php


You will find all kinds of radiation patterns that engineers can utilize to best suit their needs.
Nov 17, 2010, 10:50 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
You could ask Mr. RC-CAM if you could borrow one from him. If not, I might be willing to send you mine, depending on how long it would be until I got it back.
Nov 18, 2010, 07:37 AM
Engineer for Christ
IBCrazy's Avatar
You need an IBCrazy Vee and an IBCrazy BiQuad
Nov 18, 2010, 08:56 AM
Registered User
Avenger GBU-1H's Avatar
Thread OP
I would very much appreciate the opportunity to run a sweep on IBcrazy's Vee's and Biquad's. I have heard and read many good things about these homebrew devices. If the sweeps are good, (no doubt they will be), this would definitely "juice up your street cred" here on the forums.

And any other antennas you guys want to send me, I can run sweeps through.

Turns out I will have this S331E through 11/29/10, then I have to sent it back to the field for some "real" work.

PM me if you are interested. Once tested, I will publish my results with pics.
Nov 18, 2010, 09:24 AM
Fly FPV, sleep; repeat
twinturbostang's Avatar
How do these results relate to the manufacturers ratings (ie: 3db, 6db, etc.)? BTW, you might post this on the rc-cam forum as well. Lots of technical guys over there. They would be interested in seeing your results, and may be able to help with the lender antennas also.
Nov 22, 2010, 10:13 PM
Member 120mph Club
ATIS's Avatar
ok, I am an aerial idiot...so the larger the db number the better the results? I have static once I get 350 feet out on 900mhz despite clear LOS. I was thinking of upgrading my TX aerial from the 2dbi omni to something. I have a diversity controler and run a 3dbi and a 5dbi RX aerial off set 90*
Nov 22, 2010, 10:20 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
The higher the db, the higher the sensitivity, but that also increases the directionality. Meaning, you can fly farther away, but can only do so in the direction the antenna is pointed.

If you can't get 350 feet, then something is really wrong with your setup.
Nov 22, 2010, 10:22 PM
Registered User
Harmonics issue? Something big if you are only getting 350 ft. More details pls
Nov 22, 2010, 10:23 PM
Member 120mph Club
ATIS's Avatar
I would get intermitant static, nothing crazy but enough to make me nervous. It might have been my flying site so I am looking forward to trying my new site. I was looking at the numbers above, the V shows a 42 db and the omni shows 29 db but both are listed as 2 dbi...so will the V give me better performance over the omni on the VTX if I dont change out my Vrx aerials?

(5 min 36 sec)
Nov 22, 2010, 10:26 PM
Fly FPV, sleep; repeat
twinturbostang's Avatar
Yeah, good point. Try flying at another site. At one site, I've gone over 1 mile with dipole antennas on the video Tx and Rx. And almost total loss of video signal at 500 feet at another site. It greatly depends on local RF pollution.
Nov 22, 2010, 10:28 PM
Member 120mph Club
ATIS's Avatar
video added to my last post
Nov 24, 2010, 07:30 PM
Member 120mph Club
ATIS's Avatar
anyone?? this thread died quick....
Nov 24, 2010, 09:00 PM
Registered User
Avenger GBU-1H's Avatar
Thread OP
Great video. Felt like I was right there in the cockpit

FYI: the db numbers on the scale are not a direct correlation to the actual gain of a given antenna.

You have to look at the entire graph as a relationship to everything else in that given bandwidth. As I explained before, the downward "dip" represents how efficient a given antenna is in a bandwidth.

Normally, when we sweep just antennas, we are required to provide a reported "worst case" number. that number is just the opposite peak number from what is represented in these graphs.

I will be uploading other graphs later which will further define this.


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