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Aerial Photography and Video > Wireless Video Links Setup Help and Advice Please

mr.rc-cam
Heliman
Location: USA

Wow, I am impressed.

From looking at your videos, your flying environment is one of the toughest around. It is a lot like where I fly my e-planes. Lots of buildings, metal sports backstops, cars, and you name it.

If you run into more troubles with intermittant interference then a more directional Rx antenna should be used. The RC-CAM GP Patch would offer a bit more gain and directivity over your PCB patch; it saved me from the multipathing issues I was having at my flying location.

But at this point do not change anything! Enjoy what you have for awhile. Good luck.

Mr. RC-CAM

05-28-2003 Over year old.

HOMEPAGE

MPA
Elite Veteran
Location: Australia

Quote
The turstile antenna is a huge success

Is there something you are telling us Julian ?

05-28-2003 Over year old.

HOMEPAGE

FlightPower
Veteran
Location: Herts UK

Hi there,

Thanks, wow is good...

The site is a local park which is 100% convenient and fine for testing electrics but nothing bigger.

FYI i'm not using the stock PCB patch on the RX. I tried this with the original patch TX that I bought and that didn't work well either, with the dipole TX is was a complete non-starter, i'm guessing a polarisation issue added to a de-tuned TX. I wanted omnidirectionality as well as functionality hence the attempt to replace both ends with dipoles.

So instead of the the PCB patch I installed (hard wired to the RX board) a 5dBi mag mount omni I purchased from the UK offices of Mobile Mark (bottom right product photo here): http://www.mobilemark.com/WLAN_ISM_antennas.html

Of course the ideal RX solution that I would prefer is a small self-contained auto-tracking Yagi (without having to wear it on my head* or drive it from a laptop

).

*I wonder, what would happen if I took the turnstile design and inverted the baseplane 45 degrees forwards, would that give me a small directional matched receving antenna?

Monte. My Futaba radio gear already worked in stock form, nothing to troubleshoot. However I agree with one thing, despite the fact the amateur approach kicks butt with results to match, I wish I had a 2.4Ghz signal strength meter

anyone know where to find one of those? - maybe my local radio HAM guy would have one?? - I could also ask him about compliance at the same time.

Regards,

Julian

05-28-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

Quote
I wanted omnidirectionality as well as functionality hence the attempt to replace both ends with dipoles.

My experience has shown that {for our mobile RF based video sources} omni Rx antennas are the worst performers out there, especially in an urban setting. They are prone to severe multipathing issues in settings like the park you fly in. Their lower gains do not help either.

I have yet to see anyone need to fly a full 360 degrees around their base station. Most of us set up at the perimeter of a flying field and go from there. That allows the use of a more directional antenna, which reduces the interference issues (your first video is full of multipathing and low RF power issues).

At some point you might run into more interference. When that time comes you should upgrade to a patch antenna. You will earn more gain and reduce destructive interference issues that cause the frustrations like you experienced. There is no need to constantly aim a typical 5-8dB patch at a moving model -- their beam spread is wide enough to allow some freedom from that. The home made "GP Patch" has been found to be better than many commercially sold PCB based patch aerials, so try it when the need comes. If that does not help then step up to a 10-14dBi Yagi.

Quote
I wonder, what would happen if I took the turnstile design and inverted the baseplane 45 degrees forwards, would that give me a small directional matched receiving antenna?

The antenna you built is not a Turnstile -- it is a typical 1/4 wave Ground Plane. You would not turn it on its side. Instead, you would point it up so that the driven element was towards the sky. This would ensure that its polarization matched the vertically mounted Tx antenna. I suspect it would perform about the same as your 5dBi whip antenna (despite looking different, they are basically one in the same).

Mr. RC-CAM

05-28-2003 Over year old.

HOMEPAGE

yb2normal
Senior Heliman
Location: Broomfield, CO

That is great news!

You have a lot of guts flying 900+ feet away!

Regards,
Bill

05-29-2003 Over year old.

HOMEPAGE

FlightPower
Veteran
Location: Herts UK

Hi Bill,

You're right, I suspect it's 300ft (not metres) multipled 3x by the excitement and relief of finally having a useable downlink.
Having said that, I haven't found the limits of the current setup so the range might well be as stated - I believe I would have the guts to send out a big acro trainer I have to that kind of range to find out.

ATB

Julian

05-29-2003 Over year old.

MPA
Elite Veteran
Location: Australia

Quote
The antenna you built is not a Turnstile -- it is a typical 1/4 wave Ground Plane.

OK so now that all clear as mud

If you dont mind me asking, exactly what antenna are you refering to that works so well.
Im sure Im not the only one here wondering.

05-29-2003 Over year old.

HOMEPAGE

FlightPower

Veteran - Location: Herts UK -

THIS ONE:

http://www.geocities.com/xcamflyer/antenna2.html

I called it a turnstile because (to my mind) that's exactly what it looks like i.e. like a turnstile (before you bend to baseplane "legs" downwards), I'm happy to go along with the technical purists if it's actually called a 1/4 wave groundplane

my one that was actually used here: http://www.btinternet.com/~autography/index9.html

Julian

05-29-2003 Over year old.

MPA
Elite Veteran
Location: Australia

Thanks Julian.

I thought I was up with all the latest twigs around but that one got me worried for a minute there I thought I was close to done with soldering up Tx twigs and this was the final one.

BTW I am going out to NESS today
I called Melb office to see where this lens had got to, they have it.
Im taking the rig over with me to try it on the spot.
Unfortunately 30k on the other side of town but its a nice sunny day.
Be back this arvo with the results on the 5.7mm.

05-29-2003 Over year old.

HOMEPAGE

mr.rc-cam
Heliman
Location: USA

Quote
I'm happy to go along with the technical purists if it's actually called a 1/4 wave groundplane.

There is a popular antenna used by some wireless video folks that is called a "Turnstile." Here are the details:

http://groups.msn.com/rccam/antenna...hoto&PhotoID=98

It looks simple, but is actually difficult to build correctly. Performance is reportedly VERY good.

RC-CAM

05-29-2003 Over year old.

HOMEPAGE

MPA
Elite Veteran
Location: Australia

So there is a turnstile
Your a champion Mr

I thought it sounded familar and seen that on your forum before.

part# RQH 1700-2500M-F
Is www.raditek.com the only one who sells them ?

Cheers

05-29-2003 Over year old.

HOMEPAGE

mr.rc-cam
Heliman
Location: USA

Quote
part# RQH 1700-2500M-F

The part is hard to find. There is a "group buy" offer on the RC-CAM forum as we speak. If you want one, then visit the forum (see link). I have nothing to do with the offer, so please direct your questions to the guy doing it.

http://groups.msn.com/rccam/general...ID_Message=7070

RC-CAM

05-29-2003 Over year old.

HOMEPAGE

FlightPower
Veteran
Location: Herts UK

Ah Ha!

The real Turnstile antenna looks Very cool. Are build instructions available?

Thank you for sharing. P.S. out of curiosity, what does the quadrature hybrid component actually do?

Julian

05-29-2003 Over year old.

mr.rc-cam
Heliman
Location: USA

Quote
what does the quadrature hybrid component actually do?

It provides a precisely controlled 180 degree phase shift that feeds the two dipole pairs.

This antenna is NOT for the casual builder. The precision required to build it is more than the average tech is accustomed to. But Cyber-Flyer's measurements show that it is a stunning performer. The instructions are pretty much what you see in the RC-CAM Antenna photo album. Just go back to the photo album link I gave and press the "Next" photo Icon.

RC-CAM

05-29-2003 Over year old.

HOMEPAGE

yb2normal
Senior Heliman
Location: Broomfield, CO

I think actually the phase shift is 90 degrees... but then again, I am very likely wrong

Bill

05-29-2003 Over year old.

HOMEPAGE

MPA
Elite Veteran
Location: Australia

I might be best to order 2 myself from raditek direct.
Doubt anyone else in Aus wants one.

The semi rigid coax could be a prob here.

What RG spec is the flex cable you use to feed the ground plane antenna. ?

05-29-2003 Over year old.

HOMEPAGE

mr.rc-cam
Heliman
Location: USA

Oops. Right you are, the crossed dipoles are fed 90 degrees out of phase.

RC-CAM

05-29-2003 Over year old.

HOMEPAGE

FlightPower
Veteran
Location: Herts UK

Update: now also in metal

Something I turned out last night, it's a 7-pronged version plus radiator built around the original full length feedline and WVC brass tube.. Technically its intended to comply with the same principles as the 4-pronged PCB version. I used the yb2 30mm measurement for all parts. I'm hoping that 7 prongs will give a more even dipersion than 4 and that the small added weight will allow it to dangle vertically to some extent. There is no hot-melt glue on the radiator at all. I will test it today & report.

Cheers!

Julian

05-29-2003 Over year old.

MPA
Elite Veteran
Location: Australia

Hot Dog!
That's a beauty.

What type of Coax are you using there ?

Im trying to get Coax here, the RG213 I use is not good but easy to get, the short RG58 is worse.

I finaly found some RG174 today, the guy will give me an offcut but they normally dont sell other than full rolls.

LMR400 is another Im looking for.
Best I can do is a fly lead with SMA and N type conector on LMR200 for $80.

Semi rigid doesnt look good for supply here.

Cant buy SMA connectors other than order a box of, still searching that one.

If I can get the spec on a few types of coax used I can try my luck on a few and see which one I can get.

Thanks
Dave

05-29-2003 Over year old.

HOMEPAGE

jaxxon
Heliman
Location: Mornington Peninsula, VIC, Australia

Hi Dave,

I met you the other day at the model shop where we discussed aerial photography.

I can probably help with coax and connectors, maybe even antennas.

We sell a lot of that gear for wireless networking which also operates at 2.4GHZ. See www.x.net.au for an idea of what we have.

Don't think you are more than 25 minutes from us.

Hope this isn't considered innapropriate to post this here as I am happy to sell at cost to a fellow RunRyder aerial photographer

05-29-2003 Over year old.

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Aerial Photography and Video > Wireless Video Links Setup Help and Advice Please

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