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Terry

-90dBm 5.8Ghz modules

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I'm seeing a lot of receivers claiming -90dBm which is a big jump from the -85dBm Airwave modules I am using. Has anyone tested these properly?

Are there any that are an easy upgrade for existing Airwave based receivers?

Do they have a compatible RSSI pin?

Terry

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I don't put much faith in the absolute sensitivity numbers that are being advertised on any of the 5.8GHz receivers. But there are some new 5.8GHz receivers that have demonstrated better sensitivity than we have seen in the past. Here's some thoughts I have on the evolution of our 5.8GHz A/V receivers.

Sensitivity Numbers:
The reason I don't like the hard sensitivity numbers that are being advertised is because we don't know how much noise was allowed in the received signal. Although there are some established tests used in the RF industry on how the numbers are measured, it is unlikely that the Chinese companies collaborated their tests and followed the same test criteria. So when one receiver manufacturer states -90dBm sensitivity, another company may call it -85dBm. Or they may say it is -95dBm. Or anything else they feel like using. So we can't just go by the advertisements and nothing else.

But for sure we (us users) can compare the performance of the popular models, which is what you (and I) would like to see. I've considered doing this, but since I work at a FPV store that sells some of these products, I suspect no one would trust my reported data. So I am reluctant to waste my time. Most of the FPV'ers that have the tools and skills to perform the tests are involved in the production or selling of FPV gear, so getting an unbiased report may be a pipe dream.

5.8GHz Chip Sets:
The Taiwan made Airwave module uses their proprietary FM receiver chips. Inside the metal sardine can is their custom chip, along with a bountiful collection of discrete parts, SAW filters, and a microcontroller. Their datasheet states it has -85dBm sensitivity.

The newer China made (Boscam, SkyRF, Foxtech, NexWaveRF, etc.) receivers have the RichWave FM receiver chip. For example, the RTC6715 chip. It too needs a big collection of parts to implement a full A/V receiver. Their datasheet states it has -85dBm sensitivity. So on paper, it should be the same as Airwave.

Anecdotal Reports:
Although the data sheets suggest that the receivers should be the same, there have been many reports that the new China made receivers provide more range. I've heard from a couple users that felt that their 200mW Boscam system had as much range as a 500mW-600mW Airwave system they had used in the past.

Better Performance:
So why the difference in performance? I suspect that is a combination of things. For example:
* The identical sensitivity numbers may have been based on different test criteria. Plus, the RichWave chip is a newer design than the Airwave chip, so perhaps it has other advantages too.
* Some Airwave users built their own video systems from Airwave modules. Construction is very critical at these frequencies and ALL the little details matter. An innocent mistake can cost a few dB's in performance.
* The commercial Airwave based FPV receivers have a RF filter on their antenna input. The China designed Richwave type receivers usually do not have the antenna filter. Deleting the filter (saves costs) could easily account for a couple dB's in more sensitivity in low noise floor environments.

* Some Richwave receiver designs are built on a single PCB (to save costs), rather than a RF module mounted to another PCB. The tighter integration can be a benefit by reducing RF losses, but this advantage depends on the construction details. For example, some airwave module designs couple the antenna's RF signal path from the main PCB to the RF module by a short jumper wire, which may induce a very small (but measurable) signal loss.

* The Richwave based receivers have about 3MHz video bandwidth, which is substantially less than the Airwave based systems. The reduced RF bandwidth increases RF sensitivity, but at the cost of reducing visual resolution.
* Some early 5.8GHz users based their negative opinions while using common linear (dipole or patch) antennas, which compromised the video system in typical FPV environments. On the other hand, many new FPV'ers to the 5.8GHz game have been blessed with circular polarized antennas (such as the Skew Planar Wheel and nifty new circular patches). On their own, the circular antenna designs have made a huge improvement to the 5.8GHz FPV flying experience. The improvement may be credited to the RF receiver, when it is the antenna that deserved some of the credit.

Airwave Compatible Receivers:
Upgrading to a "-90dBm" receiver that will work with your Airwave vTx's would require that you retire your existing receivers and buy compatible models with the higher advertised sensitivity spec. For example, ImmersionRC/FatShark has new vRx products with the Richwave chip that is marketed under their NexWaveRF name. FWIW, in a couple weeks I will be evaluating a customized Boscam RC305 type receiver with the Airwave frequencies (instead of their existing non-Airwave frequencies).

RSSI:
The RichWave receivers have RSSI. But the scaling is not the same as Airwave, so your custom application *may* need some modifications.

Is it Worth the Trouble to Upgrade?
Probably, or Maybe, depending on the situation. You're an ideal guy that should do a side by side test (Airwave vs. RichWave) and tell us what you think.

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Wow many thanks for the very extensive evaluation!

As you know I am very much against the just taking the theoretical numbers at face value, I argued Thomas S on that more than once :)

I for sure would love to do some side by side testing of one of the new modules when you get them. I dont want to swap out all 7 of the receivers I am currently using without being sure of some sort of solid improvement!

I prefer to use a modest 100mW TX due to the cool running, low power requirements, very clean video as no switcher needed so even a small increase at the RX end is worth having.

Terry

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Quote

I for sure would love to do some side by side testing of one of the new modules when you get them.

Very good, we can talk about that after I have my hands on one.

BTW, if you need stereo audio (for mic and data) then you'll need to use a NexWaveRF "UNO" receiver, which retails for about $70 USD each. From what I have seen so far, all the other Richwave based vRx's are mono audio.

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At this point mono or stereo makes no difference as I dont use audio.

My plan when I get the receivers is to first do a side by side ground test with a very low power TX and note the point that each receiver loses a usable picture. I will then repeat the test in the air with a 100mW TX and record the 2 monitors with a camcorder, with luck I should be able to see the distance info on the OSD.

Terry

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OK I did some testing today, I don't claim
it’s perfect as I would need to test a number of each type to be sure. As it is
I have one of the Fatshark modules and one of the Airwave modules both with
Fatshark CP aerials. I could be that I have a very good Airwave module and a
poor Fatshark module I just dont know!


The TX was an Airwave 15mW with an 8dB
attenuator witch if I have worked it out right is about 2.4mW with another
Fatshark CP aerial. I used such a low power to keep range low as I flew it out
with my quad using visual to control it.


Both receivers were side by side with
identical aerials and monitors, the monitors are known to be very fussy of
video quality so would show up any poor signal. I used a camera on a tripod
pointed at the screens to record them and allow me to study the results later.


I flew 3 flights in different directions and
noted the max distance I could read from each then averaged it and worked it
out as a percentage. On my test the Fatshark gave 28% more range, not as good
as some seem to be claiming but a clear advantage. I will not be throwing out
all my Airwave modules just yet but if I can overcome the problem of no RSSI
pin then any new receiving systems will use this module.


One surprise was that I could read the OSD at
1168ft with basic CP aerials on 2.4mW, much further than I was expecting.



Terry

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On my test the Fatshark gave 28% more range, not as good as some seem to be claiming but a clear advantage.

That helps us understand the sensitivity of your Airwave module. Detailed specs to the new Fatshark receiver are not available. But assuming the Fatshark Nexwave Rx's Richwave IC can achieve -90dBm, then after Fatshark's antenna bandpass filter, it would be about -88dBm. After factoring the 28% decrease in range with your DiY Airwave Rx, my best estimate is that the Airwave is about -86dBm.

Keep in mind that a DiY Airwave Rx does not have the bandpass filter, so in a low noise floor environment it would be slightly better than the older commercially made Fatsharks or IRC Rxs that do not use the Nexwave module. Plus, if you are using dpcav.com's old DiY 5.8GHz Rx PCB kit (I think you are) then its RF input coupling is slight more efficient, which gives it another advantage over the commercial versions that used a short jumper connection that can increase RF losses. In other words, if your range test comparison was old FatShark versus the new Nexwave Fatshark, then you would have seen a more dramatic range increase.

One surprise was that I could read the OSD at 1168ft with basic CP aerials on 2.4mW, much further than I was expecting.

That is fantastic. How would this range have compared to your original antenna system? Did you notice less multipath dropouts with the CP antennas?

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Yes if I factor that up I should get some stunning range with a proper TX. To be honest I didnt see any real improvement in drops but thats probably because I normally use a 14dBi patch. Its a bit apples and pears, if I had been using dipoles then I would probably of seen a drastic improvement.

Im glad you made sense of the 28% increase that would explain what I got. Im sure it was quite accurate as it was very close to my previous results with the dipoles and walk test. As I said well worth using these modules if I can find the RSSI.

Terry

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Where is the RSSI found?

The FatShark Rx pinout is the same as the Airwave AWM662FRX footprint. So to find the RSSI pad you can use the information published in Airwave's datasheet. Here are some pages from it:

post-2-0-49151400-1362769007_thumb.jpg

post-2-0-24084500-1362769025_thumb.jpg

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Ah ok I got it, it works backwards to the others though dosnt it?

I got 0.8v no signal and 2.2 full signal.

Terry

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There's a variety of RSSI formats out there. So you have to bend with the wind. :)

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No problem to change my program but Im sure the Airwave modules work less voltage=higher signal, thats odd if they are accentually the same.

Terry

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That is correct -- Airwave 5.8GHz module's RSSI voltage works as you mentioned. But in the industry there's no standard in how RSSI is scaled and not all modules use an inverted RSSI signal like Airwave. There's no right or wrong, it's just one of those nuisances we DiY'ers have to accommodate.

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Well its worth remembering when I build my next tracker!

In the short term I may well just use a new module to replace the centre video receiver in my current system and continue use the old Airwave receivers to do the tracking. This system has been used to 3.5 miles so if the tracking receivers lose signal past that it will just stay put and the aircraft wont move left or right by much so should give more range with minimum effort.

Im still not sure what the new tracker will use when I eventually find time to build it, I have some 16dBi patches already but Im tempted to try helical's again.

Terry

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