Antenna exstension

[Colorado-rc 0]

Hello everyone,

I know the more popular method of mounting the antenna, is directly to the transmitter. On my particular installation, it would be easier to use a 2" to 3" extension from the transmitter to the antenna. Does anyone foresee any problems in doing this?

I'll be using either 2.4Ghz or 900Mhz, depending on where I'm at. Which coax cable should I use? Will the cable differ from 2.4 to 900?

Thanks for any help,

James

[Terry 5]

A short extension like that will not be a problem, just buy a ready made one to be sure of good connections.

Both 900 and 2.4 I guess will be the same, 50R or 75R cable, I have mixed them and not noticed the difference so dont worry.

Terry

[Mr.RC-Cam 121]

From my measurements, using a short quality extension on 900MHz systems does not cause any issues at all. But I'd avoid extensions at 2.4GHz, even short ones.

[Colorado-rc 0]

Thanks for the quick replies.

Whats the reason to avoid it on 2.4? Not that I don't trust you, just I'm not very shabby on electronics.

Thanks,

James

[Colorado-rc 0]

Just to let you guys know. The reason I would like to be able to switch between 2.4 and 900, is i plan to use this rig during fun-flys, warbird events etc. etc. With most people jumping on the 2.4 control bandwagon, I don't want to have problems. From what I hear, I can get better performance for long distance with 2.4Ghz. Which I would use solo, or with very little other people around. Is this correct? Or would I just be wasting money, on the different setups?

[Mr.RC-Cam 121]

Whats the reason to avoid it on 2.4? Not that I don't trust you, just I'm not very shabby on electronics.

The RF losses through the coax and connectors is 3X higher at 2.4GHz. So, I tend to recommend avoiding it at 2.4GHz and higher.

[Colorado-rc 0]

ah ok, good to know. Thanks. Well, if that's the case, I will probably just use 900Mhz. I don't think I can avoid using an extension, with the way its installed.

James

Edited October 2, 2009 by Colorado-rc

[Terry 5]

The RF losses through the coax and connectors is 3X higher at 2.4GHz. So, I tend to recommend avoiding it at 2.4GHz and higher.

While I agree with that statement I must point out when used on a TX its not a big issue, I have never noticed the reduced range. Also IF it were a problem then an increase in TX power would be easy.

Even on my 5.8Ghz RX the 4" extensions do not seem to be an issue, I have had a 1 mile range with only a simple dipole and flat plate reflector on 100mW.

Terry

[Mr.RC-Cam 121]

Even on my 5.8Ghz RX the 4" extensions do not seem to be an issue, I have had a 1 mile range with only a simple dipole and flat plate reflector on 100mW.

Yes, that is amazing results for only 100mW/5.8GHz , so I can't argue with success. The RG-400 based cable you are using is good stuff!

Here is an estimated way to determine cable loss for VERY high quality SMA cables:

SMA Connector loss (per connector): 0.07*SQR-ROOT Frequency (in GHz).

+

Typical Coax Loss for popular microwave rated coax material:

RG400: 2.4GHz = 0.3dB/FT, 5.8GHz = 0.6dB/FT.

RG316: 2.4GHz = 0.5dB/FT, 5.8GHz = 1.2dB/FT.

These two coax materials are nice for use at the 2.4Ghz to 5.8Ghz wireless A/V frequencies. For other cable types or frequency ratings, just look up the mfg's specs.

However, these values do NOT include the constructed cable's reflected losses, which are often very cruel; Sometimes the biggest contributor to reducing the performance of our microwave antennas.

[Chairwolf 0]

Hello,

I'm new to FPV and am planning to make the GP Patch antenna for 900mhz. My VRX (DPCAV) has the antenna connector on the same side of the box as the cable jacks, so putting the GP Patch will cover the jacks that my cables for power and signal plug into.

Questions are: (1) where can I get the short extension cables, and/or (2) is there an adjustable angle connector that can be used to move the patch from a flat angle to another angle, which would allow access to the cable jacks (sort of like the connector that comes on most whip antennas)?

Thanks for your help, and thanks RC-CAM for this site!

Bob

[Terry 5]

I don't know what country you are in but ebay is worth a look.

Try two 90deg connectors together to give an adjustable coupling.

Terry

[Chairwolf 0]

I don't know what country you are in but ebay is worth a look.

Try two 90deg connectors together to give an adjustable coupling.

Terry

Great idea! Thanks. I'm in the good ol' U.S. of A.

Bob

[PatrickLupo 0]

Word of Warning on SMA Extension Cables:

I originally ordered the Hawking RP-SMA extension cable from Amazon (also mis-labeled as SMA on Buy.com), only to find that my 1280 MHz NGHobbies video receiver used a normal (non-reversed polarity) SMA cable. Regular SMA extension cables are difficult to find for a good price in lengths of less then 25ft. Be sure to identify if your receiver uses either SMA or RP-SMA connectors on both ends. After a LOT of searching, I finally found and ordered the following cable and it fit great. (Haven't field tested it yet though)

http://cgi.ebay.com/ws/eBayISAPI.dl...em=230304656150

A good way to determine whether your receiver uses SMA or RP-SMA is to compare it to a normal WiFi router or access point. If your rubber duck antenna fits your router, then it's RP-SMA. If not then it's just plain SMA and is sometimes reffered to as a GPS extension cable. Heres the RP-SMA version.

http://www.amazon.com/Hawking-RP-SM...56273586&sr=8-1