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Pumpkin drop event

Help choosing second antenna for 5.8GHz diversity - patch or crosshair

#1
I'm upgrading my ground station (after discovering the limits of my current setup :black_eyed:) I have a Boscam D58-2 diversity receiver and VAS - 5.8 GHz Mad Mushroom Antenna (RHCP) on the way.

I'd really like some help choosing a second antenna, I'm looking at these two right now:

My Blackout and Fortis Titan both have 200mw Boscam TXs with cloverleaf antennas.

On paper the crosshair sounds great but I'm not sure it really offers much over the patch which looks more compact and durable, the prices are pretty close.

The end goal is to build something like this 30 minute ground station but with an angled back to hold an 8" LCD (imagine a wedge shape on top of a tripod).

Performance wise I'd like a really solid 3km setup but 5km would be better and mean I won't need to upgrade when I build a versa wing for longer range in the next few months.

I'd really appreciate some input, especially from anyone who has experience with the crosshair.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#2
Gothikon,

Welcome to the forum!

No hands-on experience with those antennas, but some things to keep in mind:

- what brand antenna do you have on your multirotors? if they're boscam/skyzone or one of the other Chinese CP antennas, they're left-hand polarized (LHCP) and they'll work at short range and fail miserably as you fly out because of the 32dB drop (~1600 x less power). it's all in the antenna, so getting matched polarization will have nothing to do with the rest of the radio gear.

- 5.8 really doesn't propagate very well in air -- the air is quite a bit less transparent at 5.8Ghz than, say, 1.2Ghz. Think of it like a perpetually hazy day . . . the farther you go up in frequency in these bands, the hazier and foggier it is, and the harder it is for a bright light to penetrate the fog. I'm not thinking your 200mw TX's are going to give you the range you want . . . and more power/directional antennas will *help*, but only so far . . . and they have other complications. Enjoy the gear for as afr as it will reach, but seriously consider dropping to one of the lower bands in both your video and control links before you push beyond the 1k mark.
 
#3
Most of my antennas are from RMRC or multiwiicopter.com and they're all RHCP. As I'm using Boscam tx/rx I've had to put RP-SMA to SMA adaptors on most of them.

I realise 5.8GHz doesn't have the same penetration as 1.2/3GHz and if I ever need longer range than this new setup will give me I'll build a new GS. However, 1.5km seems pretty common with cloverleaf antennas so I figured 3-5km was reasonable with a patch, helical or otherwise – I actually thought I heard them talk about getting 10-15km on a recent episode of FT where they showed the new IRC patch...
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#4
GoitHikon,

Again, I've got no experience with these antennas (good to hear you're using matched polarity -- you never know when people don't when brands get mixed and matched), but just looking at the numbers . . .

the Spironet Patch is rated for a 13dB gain -- quite a bit better than the ~1.5db gain you could hope for out of a standard cloverleaf . . . but . . .

With a 13db gain, you've got a little over 4 doublings of the power, so a little over 16 times the power. unfortunatly due to spreading loss, your range will only increase by the square root of the power, so in-beam you're looking at roughly 4x the range. the 10dB increase on the crosshair, however, will only give you a 3x increase.

*IF* you're getting a solid link out to 1.5km, they're spec'ing a similar link out to ~6km in the main beam of the spironet, and ~4.5km on the crosshair.

Now how solid is solid? I've got similar VTX gear and a fairly good RTX and I'm getting what I'd call a *solid* link out to ~150-200m (with altitude) and a weak link after that -- occasional strong glitches and patches of snow. This will depend *GREATLY* on your environment and the cleanliness of your setup. I'm flying out in the country, but there are houses and a cell tower in the area -- I don't have the tools at hand to measure the noise floor and if I did you'd probably have no way to compare it. As for my cleanliness, I've only added an LC filter to the power line, and the antenna sticks out of the bottom of the frame clear of the ESCs and control RX . . . wouldn't affect the video link nearly as much as the contorl link which seems to hold well beyond that.

And one more point . . . keep in mind you don't get something for nothing. The higher gain you recieve from the spironet comes directly at the cost of beamwidth. The FOV of these antennas is still pretty wide compared to what most truly long-range antennas do, but you will want to keep your airframe much closer to center in front of the spironet. On the spironet, 35 degrees at 3km is quite a bit of sky to fly in, but the edge of the beam will drop off pretty fast. The 120 degrees on the crosshair is nearly hemispherical, and the edges won't be nearly as sharp. Close-in, the diversity can help when you wander out of beam, but the omni on the other port will do you no good if you fly out of the spironet's main beam at range -- both antennas will suddenly be equally bad.
 
#5
I think I'm going to go with the crosshair, it's physically smaller than I first thought which was one of my main concerns and the beam is significantly wider.

Hopefully this plus the cloverleaf will give me a good 2.5km out front and a bit of all round coverage, I can turn the ground station if I decide to fly off to the side too far.

In my favourite flying spot I currently get ~1km without too many issues and that's with a poorly placed vTX antenna (not far enough away from the frame on the BO so it was partially blocked at certain angles), 3-5km may have been a bit unrealistic and to be honest without a better failsafe setup on the Naze32+Baseflight I'm not sure how keen I am on going that far at the moment. I think it's time to investigate Harakiri ;)
 
#6
I'm upgrading my ground station (after discovering the limits of my current setup :black_eyed:) I have a Boscam D58-2 diversity receiver and VAS - 5.8 GHz Mad Mushroom Antenna (RHCP) on the way.

I'd really like some help choosing a second antenna, I'm looking at these two right now:

My Blackout and Fortis Titan both have 200mw Boscam TXs with cloverleaf antennas.

On paper the crosshair sounds great but I'm not sure it really offers much over the patch which looks more compact and durable, the prices are pretty close.

The end goal is to build something like this 30 minute ground station but with an angled back to hold an 8" LCD (imagine a wedge shape on top of a tripod).

Performance wise I'd like a really solid 3km setup but 5km would be better and mean I won't need to upgrade when I build a versa wing for longer range in the next few months.

I'd really appreciate some input, especially from anyone who has experience with the crosshair.
I am new to this forum, but I am an RF technician by trade.

As has been said elsewhere in this thread the higher the frequency the worse your free air propagation will be Ie in my work to make an 800 mhz radio system perform as well as say VHF(133-175Mhz) with the same input power from your TX you require +15db gain in the antenna system. Given the input power I think max in the band is 500Mw a 15db gain is like 5w which from experience tells me that you will just notice a difference ie. if you get 1 km you might get 2.5 on a good day. Keep in mind that humidity will play a role in DX also and at these freqs can reduce range by as much as 90%

I would and will be going with the easyUHF 400 mhz radio for RC on my taranis and for video I think 900 Mhz or 1.2 Ghz for the range capability.

the other way is to toss some $$$ at what you have High gain directional antenna and an active RSSI following antenna control system to aim it. also remember the higher you can get your antenna the better, there are portable tower systems that can go 40 feet up and will fit in my car (2001 sunfire coupe) for a price...

This reminds me of my drag racing days.... "Speed costs money son, how fast would you like to go?" anyone can build a 10 second car given enough money...
 
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#7
Thanks for all the input guys.

So, despite what I said earlier, I ended up ordering the IRC Patch antenna, mostly because it was in stock locally and I think it'll help with building a more compact and more durable ground station.

If I want to go further I'll definitely put together a 1.2 or 1.3GHz setup and I'll probably get an EzUHF module later this year in preparation for longer flights. I think this antenna will be my last investment in 5.8GHz gear - just trying to put together a nice compact setup.
 
#8
I'm upgrading my ground station (after discovering the limits of my current setup :black_eyed:) I have a Boscam D58-2 diversity receiver and VAS - 5.8 GHz Mad Mushroom Antenna (RHCP) on the way.

I'd really like some help choosing a second antenna, I'm looking at these two right now:

My Blackout and Fortis Titan both have 200mw Boscam TXs with cloverleaf antennas.

On paper the crosshair sounds great but I'm not sure it really offers much over the patch which looks more compact and durable, the prices are pretty close.

The end goal is to build something like this 30 minute ground station but with an angled back to hold an 8" LCD (imagine a wedge shape on top of a tripod).

Performance wise I'd like a really solid 3km setup but 5km would be better and mean I won't need to upgrade when I build a versa wing for longer range in the next few months.

I'd really appreciate some input, especially from anyone who has experience with the crosshair.
I am using the spironet on my diversity setup with a cloverleaf. I have gone out 4.3km on this setup.(could have gone farther but battery was getting low.)
 

joshuabardwell

Senior Member
Mentor
#9
The issue with range being worse as frequency goes up, all else being equal, relates to Free Space Path Loss (FSPL). The formula for FSPL is:

FSPL(dB) = 20 * log10(d) + 20 * log10(f) - 147.55

Where d is in km and f is in MHz.

The most basic form of RF signal attenuation relates to the geometric expansion of the signal's wave-front as it expands away from the transmitter. Think of a spherical balloon. Think about how the balloon gets thinner as it blows up. That's what happens to the energy density as the RF signal propagates away from the transmitting antenna. This geometric relationship is why RF signal loss follows the inverse-square law.

But geometric expansion of the wavefront doesn't explain why the FSPL is frequency-dependent. In fact, geometric expansion is independent of frequency. Wikipedia explains it well:

The answer is that path loss is defined on the use of an isotropic receiving antenna. Hence path loss is a convenient tool; it represents a hypothetical received-power loss that would occur if the receiving antenna were isotropic. Therefore, FSPL can be viewed as a convenient collection of terms that have been assigned the unfortunate name path loss. This name calls up an image of purely geometric effect and fails to emphasize the requirement that the hypothetical receiving antenna be isotropic.
Since the hypothetical receiving antenna used in the FSPL equation is assumed to be isotropic, it has a fixed aperture. Antenna aperture is a term that defines how effective an antenna is at receiving the power of radio waves. Since antenna aperture is frequency-dependent, since antenna aperture is related to antenna gain, and since the FSPL equation assumes an isotropic antenna (i.e. the same aperture is used for all frequencies), the FSPL equation produces results that are frequency-dependent.

Wikipedia sums this up well:

In simple terms the frequency dependency of the path loss can be explained like this: with the increase of the frequency the requirement to keep the gain of the receiving antenna intact will cause an antenna aperture to be decreased, which will result in less energy being captured with the smaller antenna, which is similar to increasing the path loss in the situation when receiving antenna gain would not have been fixed.
The takeaway message, first, is that the common statement, "higher frequencies don't propagate as well," is incomplete. In fact, radio waves all are affected equally by the geometric expansion of their wavefront, regardless of frequency. It's only when you introduce an antenna and try to receive the signal that you get frequency-dependent effects--but this is entirely an effect of the antenna aperture, and doesn't relate at all to the environment "absorbing" the signal in some way.

Importantly, this discussion completely ignores environmental effects like the absorption of RF energy by atmospheric moisture, or the 60-GHz oxygen absorption peak, which are frequency-dependent absorption effects.
 
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