broken rx antenna... fixable???

[plane_tech]

hello all....
in this thread:
http://www.rcgroups.com/forums/showthread.php?t=883537
my carnage is visable.. on to the question


in the crash one of the antennas on my Futaba 6EX 2.4ghz rx was cut. Is it advisable or possible to fix this? Or should I send it back to Futaba? It was cut approx 1/32" from the case...

not sure if this was the right forum for this or not, but I figured I would try.

[Brandano]

Wouldn't worry about the antenna, that can be replaced, or the remainder of its length can be spliced on. The length isn't overly critical either, though it should be an armonic of the frequency used to be optimal (and should be straight, and aligned to the transmitter field... too much theory, in practice it's better just do a range test). I'd be more worried about the crystals, and perhaps of any solder joint failing in the crash. Better open up the RX case and check at least visually that everything is fine, and then do an accurate range test.

[Rodney]

Brandano is so very WRONG, WRONG, WRONG on this. 2.4GHz antenna are quite critical on length. These are really small coax with a precise amount of the center conductor exposed as an antenna. The safest way (unless you are a very competent microwave antenna expert) to have this corrected is to return it to the factory.

[pilotpete2]

OK,the damaged antenna cannot be repaired, but they are user replaceable. :cool:
Here's how to order: :)
http://www.rcuniverse.com/forum/m_7475304/tm.htm
Cheers,
Pete

[Julez]

http://christian-hanke.blogspot.com/2008/03/change-length-of-futaba-antenna.html

Get a Pigtail with U.FL connector and make it yourself.

[Brandano]

Oops, didn't realize this was a microwave aerial (mea culpa, mea maxima culpa. should read posts better before replying). In that case it probably is a coax with a quarter wavelength of the central conductor exposed (usually 3.0 to 3.3 cm). Even though the length is critical, most times this isn0't so accurate as you would think. There's some interesting designs out there, mainly made for WIFI connections. However these are usually highly directional and won't work well from all angles. There are some designs that are studied to be omni-directional, at least radially. This is one such example: http://zedomax.com/blog/2007/01/17/diy-homemade-24ghz-antenna/
In any case, I stand by my first affirmation that you'll better range test everything( and with these frequencies at various attitudes too) before attempting to fly that receiver again.

[plane_tech]

called Futaba, they sell a replacement, but it must be ordered from a dealer special order for $8.20.... thanks for the help! hopefully I will be able to get it sooner than later...

[vintage1]

2.4Ghz antennae ARE tuned, but even so they are not machined to the last thou!

They also have to operate over a range of frequencies..the whole band is several MHZ wide. So they couldn't be that sharply tuned in any case.

I don't know exactly what you have there, but making something out of usually high frequency coax with some bare bits that measures the same as the original will work.

OTOH is spending the dollars is not an issue,why fret about it? buy the real thing.

[plane_tech]

for $8.20, i will just buy the real one. It would cost more than that to go get the coax anyway.. its not something that I keep around. at least not that small

[tvdude310]

One thing to consider:

A TRANSMIT antenna is critical in length and other characteristics. A Rx antenna (while still important) is not really required to be as critical. As mentioned, it is tuned for a band of frequencies and will usually be a little bit longer than the required length. As long as there are no other damaged points on the wire, you should be able to splice it back on and not notice any appreciable difference in performance as long as you don't have to cut any significant length from it to make the repair.

[pilotpete2]

tvdude,
I don't think you realize that the fasst antennae are made of coaxial cable, the actual tuned element is the 30mm area at the end of the coax that has had the shield removed to create the active element. No way you would want to try repairing that small gauge coax feed line.
Pete

[tvdude310]

tvdude,
I don't think you realize that the fasst antennae are made of coaxial cable, the actual tuned element is the 30mm area at the end of the coax that has had the shield removed to create the active element. No way you would want to try repairing that small gauge coax feed line.
Pete
Hmmm...
You're right, I had no idea. And I probably would not repair it. I'd spend the $8 and replace it.
In my head I was thinking of the typical long wire antenna. :o
The only 2.4ghz stuff I have is a single microheli. The antennae are far from optimal, but since it's an indoor flyer you really can't get far enough away from it to worry about range or antenna tuning. The Rx antenna is just a 2 inch wire, the Tx antenna is a piece of small coax stuffed up into a duck-type housing.
The only reason I'm sticking with 72mhz gear is because I'm building an FPV ship with 2.4ghz video downlink.
I considered 900mhz video gear, but most of the 900mhz band is technically not legal unless you're licensed (which I should be, but am not :o ).

[Julez]

When replacing the antenna, work careful and precise. Do not pry off the connector with a screwdriver or so.
I take small precise pliers for a firm grip, and pull the connector off the base without tilting or turning it. This is important.

[plane_tech]

well the word for the LHS is that they are not yet available... go figure. The futabe rep told them for me to send the rx back and they will replace it... makes no sense to me. now instead of 9 bucks to fix a simple antenna, I have to pay for shipping for the whole rx... gotta love it....

[plane_tech]

duplicate