Espritmodel.com Telemetry Radio
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Old Jan 19, 2010, 09:33 AM
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Renatoa's dipole in his post will work fine. There is an explanation on how to build it on the second page of this thread somewhere. Basically you just strip a peice of RG174 coaxial cable and fold the shield over so that the shield and the wire are both 95% of your quarter wave. So your elements would be: length in cm = 7125/F in MHz. Use your exact frequency for best results.

You can also make a halfwave whip out of that antenna. Take the antenna apart by unscrewing the plastic base. Inside you'll see a pin with a depression where the sping sets. Solder a peice of wire directly to that unit and then cover the joint with a small peice of heat shrink. The wire should be: length in cm = 14250/F in MHz. Again, use your exact fequency. 1.2 GHz could be anything from 1200 MHz to 1350 MHz. Better to get it close for best results. Also, you will want to cut away the top part of the old antenna mount so you can get to the pin to solder it. This also gives you a better signal and makes it lighter
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Old Jan 19, 2010, 04:06 PM
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Dos Hermanas (Sevilla)
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Quote:
Originally Posted by RENATOA View Post
8 grams. If interested I can post build log, I took pictures.
http://www.rcgroups.com/forums/showp...&postcount=143
Thank you very much Renatoa, yes, you can post the build log.

Regards.

Patrick
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Old Jan 19, 2010, 04:11 PM
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Quote:
Originally Posted by IBCrazy View Post
Renatoa's dipole in his post will work fine. There is an explanation on how to build it on the second page of this thread somewhere. Basically you just strip a peice of RG174 coaxial cable and fold the shield over so that the shield and the wire are both 95% of your quarter wave. So your elements would be: length in cm = 7125/F in MHz. Use your exact frequency for best results.

You can also make a halfwave whip out of that antenna. Take the antenna apart by unscrewing the plastic base. Inside you'll see a pin with a depression where the sping sets. Solder a peice of wire directly to that unit and then cover the joint with a small peice of heat shrink. The wire should be: length in cm = 14250/F in MHz. Again, use your exact fequency. 1.2 GHz could be anything from 1200 MHz to 1350 MHz. Better to get it close for best results. Also, you will want to cut away the top part of the old antenna mount so you can get to the pin to solder it. This also gives you a better signal and makes it lighter
Thank you IBCrazy, i will try it, it does'nt matter if it is not flexible, for me the most important part is the weight, the trex 250se is so tiny that i have to calculate every added gramm..
Thank's again.

Regards.

Patrick
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Old Jan 20, 2010, 02:21 AM
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Originally Posted by Patrick R View Post
Thank you very much Renatoa, yes, you can post the build log.

Regards.

Patrick
Ok, here is how I made that antenna. Started with a cable as in first image, I seen similar on eBay, mine was from an industrial equipment out of use.
2nd image - Cut it to a length close to the original antenna, then strip away the outer insulation for 60mm. 1/4 wave for 1280 mhz is 55.6mm, so I let some milimeters to play. I expect it to be finally even shorter, due to the velocity factor of coax plastic, will be somewhere in the 50-52mm range.
3rd image - starting push down the mesh as in rc-cam page, and... surprise. The cable is *double* shielded ! I must change the approach, such mesh can't be "turtleneck" over the coax's jacket, is too rigid, the inner shield especially, no way to enlarge it. So I started to unbraid the outer shield first.
4th image - outer shield completely unraveled, will follow the inner and after you finish all you have to do is to wrap the shield wires with heat shrink and you are done.
Fine tuning follows if you have RSSI for video receiver, else cut it at 52mm, must be a good estimation.
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Old Feb 04, 2010, 03:29 PM
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I went a little coax crazy myself last night! I fixed a broken stock 2.4 gHz, made two versions of the inverted vee for 2.4 gHz and 1.28 gHz, and made my own Dipole for the tx and rx I couldn't get my hands on RG 174 or anything but 58, but I went for it anyway. Later I found some coax with F connectors that fit my BestOfferBuy fox 700, so I just hacked that into a Dipole for the rx... I figured why not!

I couldn't get the sheilding to fold over cleanly like shown by RC cam, so I added a wrap of aluminum foil for the ground sheild on my dipole(s) just cuzz. Not sure it its doing anything but I did get contiuinty to the SMA ground. I really have no clue what I'm doing but I'm playing with the rcexplorer calculator and your ideas here and so far everything I've done is working better than the stock antennas, (to be honest I haven't booted up my 2.4 ones yet but the 1.28 stuff is all working great!) and they worked pretty well!

Next up is a patch for the rx
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Old Feb 07, 2010, 03:16 PM
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Hi IBCrazy-

So, I have one of these transmitters (below), and it's going to be uncased, and put on a small FPV plane. The thing is that the antenna is way to big like that- what's the best way to make it lighter? Could I do something like the 2nd picture? If so, how?

Thanks!




2)
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Old Feb 07, 2010, 05:00 PM
Dizi
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this model is it good for tx and rx video or only the rx?
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Old Feb 07, 2010, 06:38 PM
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Funjet - The reason there are so many types of antennas is that they are all so different. Every antenna is just as good for receiving as it is for transmitting. You need to make an antenna that best suits your needs. Those are much better suited for stationary radio communications.

@KMART - I'd build an inverted Vee antenna for a small model. They are more efficient than a monopole (such as in the second picture). However a monopole (1/2 wave) will work fine. If you are building an aerobatic plane, go with an inverted Vee antenna with a 30 degree angle. Otherwise, I'd build a half wave dipole.
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Old Mar 19, 2010, 08:20 PM
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I tried to build the monopole 1/4 lambda antenna for tx but ended with a difficult folding back the mesh over the jacket. Can I use the approach presented in the first image?

Is the RG316 coax cable. (see second image).


Thanks
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Old Mar 19, 2010, 08:39 PM
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Unfortunately, no it won't. The braid is still acting as shielding. However, you can repair it!

Take some heat shrink tubing and cover up all of the braid except for the very top. Then solder on a 1/4 lamba wire to the top of the braid. Run that along the heatshrink tubing. All fixed

Quote:
Originally Posted by HF_ATL View Post
I tried to build the monopole 1/4 lambda antenna for tx but ended with a difficult folding back the mesh over the jacket. Can I use the approach presented in the first image?

Is the RG316 coax cable. (see second image).


Thanks
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Old Mar 20, 2010, 02:22 AM
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You can unbraid it, as #64 last image.
Then, cover it with Aluminium foil, and finaly wrap it with heat shrink, or simply tape. Will work at same parameters.
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Old Mar 20, 2010, 03:27 AM
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Great thread IBCrazy ,ive been looking for more info for awhile . Subscribed.
Regards Liam.
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Old Mar 20, 2010, 06:21 AM
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These are much lighter too, especially the dipoles compared to stock antennae that come with the Fox (or BOB) combos.

I use RG316 to make mine. Main thing is not to damage the braided shield when removing the outer most insulation which will make folding over very difficult (try a light cut around the circumference at where the insulation to be removed, then a bit of heat with a heat gun makes pulling out the insulation much easier, )
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Old Mar 20, 2010, 09:33 AM
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Portugal
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Quote:
Originally Posted by IBCrazy View Post
Unfortunately, no it won't. The braid is still acting as shielding. However, you can repair it!

Take some heat shrink tubing and cover up all of the braid except for the very top. Then solder on a 1/4 lamba wire to the top of the braid. Run that along the heatshrink tubing. All fixed
Thanks for the idea IBCrazy.
The 1/4 lambda wire I should solder can be of any type of wire (with plastic isolation)? It have to be running outside the heatshrink tubing and then use another heatshrink tubing to protect it, right?
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Old Mar 20, 2010, 09:36 AM
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Quote:
Originally Posted by RENATOA View Post
You can unbraid it, as #64 last image.
Then, cover it with Aluminium foil, and finaly wrap it with heat shrink, or simply tape. Will work at same parameters.
Thanks RENATOA.
How can I unbraid it? Cutting a bit the shield's braid and pushing it back?
I am not seeing how can I pushing it back over the jacket because it simply don't get back..
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