I’ve seen and heard many people refer to the popular “mushroom” antenna as not having nulls and is more efficient than the common dipole antenna. This is just not true.
This is a 2D beam plot of a typical mushroom or Cloverleaf antenna as viewed vertically. As you can see, and as Karl correctly stated, there is a very sharp null directly above the antenna (and if it was in free space, directly below).
The primary differences of the mushroom antenna, the proper name being a Skew Planar, are:
The dipole is linearly polarised where as the skew planar is circularly polarised.
The dipole has a theoretical gain of around 2.15dBi and the skew planar has a theoretical gain of approximately 1.6dBi to 2dBi. The variance is due to and determined by the angle of the individual elements and the length of the coax feeding the antenna.
The primary purpose of using a skew planar antenna in FPV is due to the fact that signals on the 5.8GHz band reflect from all kinds of mediums: the ground, nearby metal objects, even regions of air with vastly different moisture densities. etc: and every time a signal is reflected the polarisation is flipped or reversed. So in theory, as long as the TX and RX antennas are the same polarisation, primary reflected signals are rejected. In practise this is sort of how it works. These signals may reflect many times before reaching the RX antenna and so there will be many variations in phase. Combining signals of differing phases can either add to or subtract from the original, 180degrees difference and equal amplitude will cancel each out. This is why while flying around and with an unobstructed view of the quad the received video will still suffer dropouts, which are more pronounced when flying close in. The skew planar antenna is more effective at rejecting signals of opposite polarity/differing phase than a dipole hence their popularity in FPV. However for long range stuff an antenna derived from a dipole, such as a Yagi-Uda Array (named after two Japanese Professors responsible for the design) but more commonly referred to as simply a Yagi, is more popular due to the simpler construction and convenience.
I’ve done it again I’m also available as an after dinner speaker, if the intent is to clear out the venue.
Not really I’m afraid. I don’t have anything that uses a mmcx connector, all my longish distance quads use SMA connectors. Of the antennas I’ve used on 5.8GHz I have been most impressed with the MenaceRC Raptors. They’re very robust and great performers, and very reasonably priced.
So I replaced the duff VTX with the new Race Ranger one but was still having huge issues. Until (and tbh I could kiss Josh Bardwell right now!) I found that AKK boards and Betaflight don’t necessarily play friendly and there is a firmware update that sorts the SmartAudio issues (which I thought I had solved but clearly hadn’t until now)
Without this, Betaflight will report that you’re on channel X and band Y, running at power Z… and it’s lying completely - it’s actually locked to 25mw. That combined with the fact that the goggles therefore also don’t actually know what channel you’re on and it’s just a recipe for disaster - as I repeatedly experienced. Additionally, due to the placing of the board when fitted wasn’t at all easy to see the LED indicators well enough to be able to tell what it was actually set to.
With that lot now sorted, I flew out to 400m this PM - solid video all the way, zero break up. I lost RX before video so I think the Crossfire is definitely on the cards.
Thanks to everyone for all the pointers - it’s been a journey getting to this point but am sooo happy it’s all now working correctly.
Bring on the flying… I got to finally (badly) chase a buddy around for a bit this PM…
@DaveJaVu what action camera are you using? I’ve been using the Osmo Action but I’m only getting about 1 n half minutes flight time on a 1500mah 4s pack. I think it’s too heavy for the quad.
I’m thinking about upgrading to the Runcam 5 orange to reduce the weight and try and get better flight times lol
Have to be to keep it in the air lol it hovers at half throttle lol its definitely too heavy. I was getting 4 minutes when I first flew it without the action cam
Just looked the Osmo is 2g lighter than the GoPro, and I would say that I’m using around 40% throttle to hover. Definitely getting way more run time than you seem to be though. Old batteries?
Brand new batteries. Only flown them twice. I’m just looking at my black box logs and the stick overlay of my flights barely goes over half throttle… so I’m not sure what’s going on.
I’m also available as an after dinner speaker, if the intent is to clear out the venue.
