|
|
05-12-2014, 10:17 AM | #1 |
Administrator
★ Site Supporter ★★ Administrator ★
I am: Max P.
Join Date: Feb 2007
Location: Aurora, Ontario
Radio of choice:
JR and Spektrum Feedback: 77 / 100%
Posts: 19,799
Total Props: 232
|
1.4 KM range with Biquad. Not bad!
Not bad for NO ANTENNA!!!
This is a cautionary note for anyone using custom made antennas. Yesterday I was wondering why my bi-quad kicked in at 100M and I had loss of picture at 1.4km. The onset of signal loss was instant. This is a departure from the gradual signal loss you would see under normal conditions. Under normal operating conditions, you usually see a bit of snow that builds up on the screen that forewarns you of eventual picture loss and that you should turn around. In this case, it happened very suddenly. One second it’s a solid picture, the next second it’s gone. It turns out that my home-made antenna had a fatigue failure at the end of the antenna where the signal wire connected to the antenna Active Element. The Active Element had broken free from the solder joint. This was caused by a succession of failures that led to vibration fatigue caused by the antenna wire bouncing up and down over who-knows how many flights. Now, to be fair, the antenna was well used. This plane has over 180 FPV flights and logged more than100 hours of FPV flying with this particular antenna. So the vibration fatigue was bound to happen. I apologize for not having pictures of the failed antenna. I had already torn it apart while investigating the root cause. Instead I have included a diagram for reference; The Coax signal wire is a fine lead. It is soldered to solid wire Active Element [PURPLE line] The ground wire is a little heavier, and is soldered to the Ground Element.[ORANGE line] The biggest mistake I made in the manufacture of this antenna was to use hot glue. Hot glue is great for convenience and quick setting. But it does not have long term holding, as I have discovered in this case. When I first made this antenna, the Inverted Vee was mounted to a plywood base that was shaped to 120 degrees [RED line]. I used hot glue to hold the elements and the coax to the base. Later, when I installed it onto the plane, I needed to extend the antenna base a little further, so I used hot glue to glue the antenna base [RED line] to the extension[BLACK line]. The extension was then mounted to the underside of the wing. The first fatigue failure point is at this joint. Airframe vibration caused this joint to crack. The resulting freedom of movement allowed the vee-shaped base[RED line] to flex even more, setting up the secondary failure. Using hot glue was a mistake. But keeping things in perspective, after 180 flights and 100 airtime hours, this is not bad. In hindsight, I should have used glue or epoxy on this joint. I could have also remade the base from a single piece of plywood, which is probably what I will do when I rebuild this antenna. The second failure point is where the Coax signal wire is soldered to the active element [ORANGE line] to BROWN line]. Again, this was a fatigue failure over time. As in the first failure, hot glue was the used to encase the coax and active element onto the plywood base. Upon inspection of the failed joint, it appears the vibration of the airframe over all those flights acted on the antenna to crack the hot glue. This allowed the element to vibrate inside its encasement just enough to eventually break the solder joint where the signal wire connects to the active element. This problem with this kind of failure is it happens very suddenly. My rebuild will have 2 fixes;
I will also add a periodic antenna inspection to my preflight inspection checklist. I encourage all FPV fliers to include an antenna inspection prior to flying. This failure mode also reinforces the need for a sharp-eyed spotter and/or a reliable RTH system.
__________________
Transport Canada Advanced Flight Examiner; RC Test Pilot; FPV Instructor, Airplane Instructor; Helicopter Instructor My Aircraft Albums: https://www.rccanada.ca/rccforum/album.php?u=13173 |
. |
Sponsored Links - Subscribe to remove this ad. |
|
05-12-2014, 10:50 AM | #2 |
RCC Senior Contributor
I am: Patrizio G.
Join Date: Oct 2006
Location: London
Radio of choice:
Turnigy 9x # of RCs: 5
Feedback: 0 / 0%
Posts: 677
Total Props: 1
|
Re: 1.4 KM range with Biquad. Not bad!
Wow max you did a full forensic anilisys of your issue, nicely don.
Do you have a RTH on that plane?
__________________
THE MINION |
. |
05-12-2014, 11:01 AM | #3 |
RCC Supreme Contributor
I am: Scott R
Join Date: May 2012
Location: VICTORIA
Radio of choice:
Frsky-Taranis # of RCs: 20
Feedback: 0 / 0%
Posts: 2,034
Total Props: 24
|
Re: 1.4 KM range with Biquad. Not bad!
also something to be said for buying high quality ready made antennas - like the ones from Circular Wireless. My CW antennas have been tough and solid.
The IBCrazy and TrueRC antennas have broken numerous times, though each generation keeps getting better. yesterday I had an antenna not screwed on tight enough. lost video just 100m out. I looked up and the plane was right in the sun! I could only wait till it dove away from the sun and landed her gently by LOS. |
. |
|
|
05-12-2014, 11:09 AM | #4 | |
Administrator
★ Site Supporter ★★ Administrator ★
I am: Max P.
Join Date: Feb 2007
Location: Aurora, Ontario
Radio of choice:
JR and Spektrum Feedback: 77 / 100%
Posts: 19,799
Total Props: 232
|
Re: 1.4 KM range with Biquad. Not bad!
Quote:
This plane DOES have RTH. It gives good peace of mind. Having said that, 1.4km is nothing for a sharp eyed spotter. We have flown much further and still had LOS spotters able to see the plane.
__________________
Transport Canada Advanced Flight Examiner; RC Test Pilot; FPV Instructor, Airplane Instructor; Helicopter Instructor My Aircraft Albums: https://www.rccanada.ca/rccforum/album.php?u=13173 |
|
. |
05-12-2014, 11:14 AM | #5 | |
Administrator
★ Site Supporter ★★ Administrator ★
I am: Max P.
Join Date: Feb 2007
Location: Aurora, Ontario
Radio of choice:
JR and Spektrum Feedback: 77 / 100%
Posts: 19,799
Total Props: 232
|
Re: 1.4 KM range with Biquad. Not bad!
Quote:
The small stuff will have little mass to cause fatigue failure of the glue joint. On the other hand,I strongly feel that 1.3G CP antennas are big enough to suffer vibration fatigue no matter what the bonding agent is. Its all about vibration and time. 900Mhz is even bigger still. Bottom line: Inspect your antennas every now and again just to be sure.
__________________
Transport Canada Advanced Flight Examiner; RC Test Pilot; FPV Instructor, Airplane Instructor; Helicopter Instructor My Aircraft Albums: https://www.rccanada.ca/rccforum/album.php?u=13173 |
|
. |
05-12-2014, 07:07 PM | #6 | |||
RCC Pro Contributor
|
Re: 1.4 KM range with Biquad. Not bad!
Tested out some new 1.2 vtx antennas. Small, light weight and low drag. To behonest, the LP's work just as well as the CP's IMO.
|
|||
. |
05-12-2014, 09:52 PM | #7 |
Administrator
★ Site Supporter ★★ Administrator ★
I am: Max P.
Join Date: Feb 2007
Location: Aurora, Ontario
Radio of choice:
JR and Spektrum Feedback: 77 / 100%
Posts: 19,799
Total Props: 232
|
Re: 1.4 KM range with Biquad. Not bad!
Those are good looking antenna's Buffy. What are they and where did you get them from?
__________________
Transport Canada Advanced Flight Examiner; RC Test Pilot; FPV Instructor, Airplane Instructor; Helicopter Instructor My Aircraft Albums: https://www.rccanada.ca/rccforum/album.php?u=13173 |
. |
05-13-2014, 07:32 AM | #8 |
Administrator
★ Site Supporter ★★ Administrator ★
I am: Max P.
Join Date: Feb 2007
Location: Aurora, Ontario
Radio of choice:
JR and Spektrum Feedback: 77 / 100%
Posts: 19,799
Total Props: 232
|
Re: 1.4 KM range with Biquad. Not bad!
Last night I took the damaged antenna, nipped off the broken and damaged end and re-soldered the antenna leads back on.
For the mounting plate, I went with a bigger piece of ply. This time I want to have the antenna magnetically mounted to the wing. The old design was held in place with a plastic tube and wire. This allowed removal of the antenna from the wing to prevent damage during handling. I used this method on this plane when it was first converted to FPV in 2012. I have since found that magnetic mounting is easier to handle and more forgiving to the odd knock at the flying field. I have used magnetic mounting on my more recent FPV projects and I really like it. So this antenna will have a magnetic mount. Here it is encased in epoxy Once the epoxy cured, I shaped the plywood. Another piece of ply will be added at right angles that will hold the magnets. The hole in the plywood near the rear is for a plastic tie-wrap that will hold the coax against the plywood.
__________________
Transport Canada Advanced Flight Examiner; RC Test Pilot; FPV Instructor, Airplane Instructor; Helicopter Instructor My Aircraft Albums: https://www.rccanada.ca/rccforum/album.php?u=13173 |
. |
05-13-2014, 02:34 PM | #9 | |
RCC Pro Contributor
|
Re: 1.4 KM range with Biquad. Not bad!
Quote:
https://www.fpvpro.com/video-transmitters-antenna |
|
. |
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
Thread Tools | |
Display Modes | |
|