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garris2

RC control Tx Yagi proximity to Video Rx Yagi

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Hi all, I have a 1.2G 12dBi Yagi mounted on my antenna tracker and I recently added a 2.4G 7dBi next to it, about 3 inches seperation.

I can't seperate the antennas any further whilst still having them on the same antenna tracker.

The 1.2G is for my video reception and the 2.4G is for my RC Tx to aeroplane.

The 1.2G is feeding into a standard Lawmate Rx channel freq 1280 (http://www.nghobbies.com/cart/index.php?main_page=product_info&cPath=1_5_93&products_id=179)

and my 2.4G is being feed by this booster (http://cgi.ebay.com.au/Powerful-2W-33-DBm-WiFi-802-11b-g-Booster-Amplifier-/250785163369?pt=AU_Computers_Networking_Accessories&hash=item3a63f5e869).

The Booster is feed from my RC Control Tx Futaba FASST 12FG TM-14 module moded with an SMA connector output.

My question is, is it bad to have the antennas mounted so close together (detrimental affects on the 1.2G system)?

I recently purchased this device 2.4G High pass filter (http://www.dpcav.com/xcart/product.php?productid=16439&cat=267&page=1)

with the idea of placing it in the feed line after the booster to the 2.4G yagi. Would it be helpful in this situation?

In reference to its position in the feed line from the Booster to the 2.4G yagi, should it be placed at the output of the Booster or the input of the antenna?

thanks v much

Geoff

Edited by garris2

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Try it !

Cant think why you want 2W of power into a 7dBi aerial though, are you trying to reach the moon?

Terry

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Hi Terry, thanks for your reply. I have tried it, 1 flight so far and it seemed to work fine. RC control was no problems although video was not as good as previously but that could also be due to the fact there were 3 of us FPVing at the same time all on the 1.2/1.3G band on different channels.

I'm wondering what general radio knowledge others have in relation to close proximity of Tx and Rx antennas.

Why do I want 2W of power into a 7dBi aerial. Well they don't make .5W boosters so you go with what you can get. The 7dBi yagi was on hand too, and of a reasonably compact size so I thought it a good stating point.

I tried the 1W booster and it worked well, the boosters are a really good solution for those that want to fly long distance and use more than 8 channels (me 12). All but one of the long range UHF systems only support 8 channels and the one long range system that does support 12 channels only does so for the Multiplex EVO12 which you can't do head tracking easily.

Using a booster with my Futaba 12FG allows me to fully use all 12 channels and have a really good head tracking setup.

When I was feeding the booster into an omni I was getting occasional Failsafes at 7km so I am trying to improve on that. For some people its about flying low around the local oval, for others its about pushing the boundries of possibility, I like to do both. Imagine if nobody had ever put a camera on their model aeroplane in the first place (why would anybody want to do that?), none of us would be doing any of this.

cheers

Geoff

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RC control was no problems although video was not as good as previously but that could also be due to the fact there were 3 of us FPVing at the same time all on the 1.2/1.3G band on different channels.

I recommend you do a simple test to see if there is any interaction.

1. Setup the tracking system station as you expect to use it. Do this outdoors, in a wide open area.

2. Connect a DMM to the RSSI pin of the video Rx.

3. Turn on the wireless video Rx, but turn *everything* else off. That is, power removed from the R/C Tx, the R/C Tx amp, and video Tx.

4. Note the RSSI voltage.

5. Repeat the test, but this time turn on the R/C Tx and its amplifier. Keep the video Tx turned off.

6. Compare the two RSSI voltages. If it has changed from step 4 then that may indicate that your video Rx antenna and R/C Tx antenna need to be further apart.

7. Repeat steps 1-6 for each of the wireless video channels (frequencies) you expect to use.

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Hi Geoff,

I was not being negitive about pushing the limits as I was pushing the limits about 10 years ago I understand the attraction ;)

I just think the TX power you are pushing is on the high side and would be surprised if your video system could keep up.

After you have done the tests Mr RC-CAM surgests I would fly out to the limit and power off your R/C TX and see if the picture improves. I assume you have RTH or some sort of autopilot?

Terry

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Thankyou again for your replys Mr RC-Cam and Terry.

I will give those tests a try as soon as I can. I actually have one of those DPCAV RSSI display meter kits connected onto the Rx already, would it be helpful in performing some testing?

In addition to the testing above I guess I could power everything up, note the RSSI level and then turn off the RC control Tx and note the reading again.

Actually thats probably not all that dissimilar to what you have suggested Terry.

Yes I do have a RTH system set up and working well. On a side note, I turned off my other RC Tx (JR) once, mid air, and it didn't end well. But I feel much more confident attempting that with my Futaba. I will do that as well and see the result.

I agree that 2W may be high but I went ahead with it because I thought 2.4G would be attenuated quite sharply at long distance, I think thats correct isn't it?

Anyway, thankyou both for your guidance.

Geoff

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I actually have one of those DPCAV RSSI display meter kits connected onto the Rx already, would it be helpful in performing some testing?

That is a perfect meter to use for this test.

In addition to the testing above I guess I could power everything up, note the RSSI level and then turn off the RC control Tx and note the reading again.

That could be useful. Keep in mind that turning off the R/C Tx will still leave the RF power amp running, so you may not see any change. Plus, the strong RF from the video Tx will probably mask any notable RSSI changes too. So be sure to perform the suggested tests first.

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Yes the RSSI meter is good but you may need to have a very low signal before any problem shows itself. If you dont want to turn off the TX in the air (just a second or two would do) then set up a low power video TX or put a dummy load on the one you have and place it on the ground a hundred feet away or whatever.

If your flying high (I never fly less than 500ft when doing long range) then 2.4Ghz is ok. Its low level where it falls short of vhf or uhf systems.

Terry

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Update:

Ok, I have tested as suggested following the proceedure in Post #4.

I applied my DMM to the RSSI output of the Lawmate receiver with all transmitters turned off. The reading was 124.4mV.

This reading was a bit low I thought, so I verified by turning the video Tx on and the RSSI went to 3.78v

I turned the video Tx off again, RSSI went to 124.4mV and then I turned on my RC Tx and WiFi Amp. Both LEDs on the Amp illuminated indicating power and signal were applied and received.

I noted the RSSI voltage of the Lawmate VRx and it was still solidly at 124.4mV

i.e. there was no observed change in the RSSI level with my 2.4G 2W Booster Amp feeding my 7dBi yagi placed at 3" separation from my 1.2G Video yagi antenna.

I've so far only made this test on my channel frequency of 1.280GHz.

I went flying on the weekend and had another good flight out to 6Km. I know this is not stunning range but I can report that video quality is better than my previous flight. The reason is that my friend has changed his video goggles repeater frequency away from mine which has improved picture quality for both of us.

I forgot to perform an RC Tx power off test that I said I would do probabily because I was having too much fun and things were working well. I will try to do that test next flight.

Geoff

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New Update.

password: 2.4G RC off

Here is a sort clip where I turn off my 2.4G RC Tx to compare what my video is like when RC is On/Off.

At about 49sec into the video I turn off my RC Tx (after RTH has manually been engaged) and I think there is a slight improvement in video quality. At the 1:26 mark I turn 2.4G RC on again and a barely perceptible decrease in video quality can be seen.

And then again at 1:43 I turn RC off and on again at 1:53

Conclusion: I think its ok in my case to have the 2.4G RC Tx Yagi positioned so close to the 1.2G VRx yagi.

Geoff

Edit: Well I just watched the video after I uploaded it to vimeo and if anybody can tell the difference in quality in that video, I go he. Recorded quality is much better, I just don't know how to make it look good for upload, sorry.

post-4774-0-52552500-1305476422_thumb.jp

post-4774-0-77705400-1305476430_thumb.jp

post-4774-0-78264700-1305476441_thumb.jp

post-4774-0-46112100-1305476449_thumb.jp

post-4774-0-45625900-1305476457_thumb.jp

Edited by garris2

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Conclusion: I think its ok in my case to have the 2.4G RC Tx Yagi positioned so close to the 1.2G VRx yagi.

Thanks for the follow-up report.

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