Aircraft Antenna Mod

[MacIak]

I was able to make a safe assumption that the Mavic aircraft does use dynamic RF transmit. And it appears to be directly related to the proximity of the remote controller to the aircraft (as expected).

I direct connected my spectrum analyzer to the radio board on the Mavic and measured a constant 8.5dB (7mW) with the remote controller sitting right next to the aircraft:

View attachment 17125

I moved the remote controller inside my microwave oven across the room and the power increased to a constant 12.5dB (18mW):

View attachment 17126

I then powered off the remote controller and the aircraft appears to go into a constant full power 20dB (100mW) beacon mode on a narrow channel not broadcasting the video stream anymore (makes sense):

View attachment 17128

I have started testing the same concept on the remote controller, but the remote TX uses frequency hopping that that is a little more difficult but I will see what I can come up with.

Those are great findings, fully confirming my thoughts of dynamic power on bird side. Should it not be transmitting 26dB as per specs in FCC??

 

[beanbubba]

Those are great findings, fully confirming my thoughts of dynamic power on bird side. Should it not be transmitting 26dB as per specs in FCC??

I was measuring at the radio board. The published EIRP of 26dBm also includes the gain from the antenna.

I am making an educated guess that the aircraft antenna gain is 3.8 dBi based on similar antennas I have worked with.

My spectrum analyzer has approximately 2dB loss in the attenuator and cable connectors.

Therefore 20dBm + 2dB + 3.8dBi = EIRP of 25.8dBm. Thats almost dead on 26dBm.

Equivalent isotropically radiated power - Wikipedia

Note that DJI published an EIRP of 26dBm, but that is far from the FCC upper limit of 36dBm EIRP and the reason Sunhams is able to sell their amp's in the US assuming the end user has a relatively low gain antenna (most of you do not, see attachment below). The US law is a little fuzzy in this area because technically the manufacturer is required to certify a "system" including all the parts that contribute to the EIRP. Nobody has certified the modified controllers plus amp's and therefore technically not legal.... BUT as long as you stay under 36dBm there is no one in a black government van that will seek you out on range test day

 

[beanbubba]

Here is a primer on the basics of calculating RF link budgets in Wifi frequencies (that DJI uses even though they don't use the 802.11 Wifi protocols, it's the same math).

 

[beanbubba]

I measured the remote controller TX with and without the sunhams amp's. There is no apparent variable output like we saw in the aircraft. It just transmits at full power from what I can see (more testing needed, this is not conclusive).

Here is direct connected to the remote and measured at 16.5dBm. If you are using the factory antenna at 3.8dBi (estimated), and account for the 2dB loss in my measurement, the EIRP would be 16.5dBm + 2dB + 3.8dBi = 22.3dBm.

If you are using the Rexuav antenna at 9dBi, and account for the 2dB loss in my measurement, the EIRP would be 16.5dBm + 2dB + 9dBi = 27.5dBm.




Here is the measurement with the sunhams in-line at 31dBm.

If you are using the Rexuav antenna at 9dBi, and accounts for the 2dB loss in my measurement, the EIRP would be 31dBm + 2dB + 9dBi = 42dBm (FCC limit is 36dBm).

 

[beanbubba]

Here is direct connect to the aircraft radio board with sunhan amp in-line and measured at 30dBm. If you are using the factory antenna at 3.8dBi (estimated), and account for the 2dB loss in my measurement, the EIRP would be 30dBm + 2dB + 3.8dBi = EIRP of 35.8dBm (just barely FCC legal).

This is the max output I observed in "beacon" mode (when controller is powered off). The other tests were inline and less power as discussed before and redundant to mention at this point.

 

[ZeeKodadii]

wow great write up and lot of info. I just had couple questions

1) Can you use two sunhams amp's on one 10dbi antenna with one connector ?
10dbi+ 30dbm +30dbm +2 db =72dbm?

2) when doing the rexuav antenna we use two sunhams amp's wouldn't that be 9dbi+30dum+30dbm+2db=71?

 

[beanbubba]

wow great write up and lot of info. I just had couple questions

1) Can you use two sunhams amp's on one 10dbi antenna with one connector ?
10dbi+ 30dbm +30dbm +2 db =72dbm?

2) when doing the rexuav antenna we use two sunhams amp's wouldn't that be 9dbi+30dum+30dbm+2db=71?

The sunhams published upper receiver sensitivity is 20dBm. You will fry one of the amp's if you try to run them in series.

 

[beanbubba]

I need a U.FL Female to U.FL Female adapter or cable. I have searched everywhere and can't find one. Without it, this means trying to solder the microscopic connector that I doubt I have the skill to do.

Here is a Male to Female example of what I am looking for:



Does anyone have a source for a U.FL Female to U.FL Female adapter or cable?

 

[dirtybum]

The sunhams published upper receiver sensitivity is 20dBm. You will fry one of the amp's if you try to run them in series.

don't know that that's entirely true Dr.bean. An antenna guru I once knew, we'll just call him Will, once shared with me and others I'm sure, the use of two amps,one of them being considered the jumper amp. only really necessary or useful with the larger antennas like 19 db panels and to be used when using longer cables. but no it does not necessarily double the amps specs

 

[beanbubba]

don't know that that's entirely true Dr.bean. An antenna guru I once knew, we'll just call him Will, once shared with me and others I'm sure, the use of two amps,one of them being considered the jumper amp. only really necessary or useful with the larger antennas like 19 db panels and to be used when using longer cables. but no it does not necessarily double the amps specs

Based on your description, your guru may have been drinking that day.

 

[dirtybum]

I need a U.FL Female to U.FL Female adapter or cable. I have searched everywhere and can't find one. Without it, this means trying to solder the microscopic connector that I doubt I have the skill to do.

Here is a Male to Female example of what I am looking for:

View attachment 17257

Does anyone have a source for a U.FL Female to U.FL Female adapter or cable?

is this it?https://www.ebay.com/itm/301694926173

 

[dirtybum]

Based on your description, your guru may have been drinking that day.

although that did make me laugh, what about my description describes him as a drinker? or what in my reply implicated that?

 

[beanbubba]

although that did make me laugh, what about my description describes him as a drinker? or what in my reply implicated that?

Specifically that amp's are necessary with large high gain antennas. Amp's are MOST needed with low gain antennas

 

[beanbubba]

is this it?IPEX UFL Female to Female Coaxial Cable 1.37mm OD 15CM | eBay

That has the right description, but the wrong picture.

 

[sprtbkrydr]

10Pcs IPX / U.FL Female to IPX / U.FL Female Coaxial Cable 1.37mm 15cm Wireless

 

[beanbubba]

I need a U.FL Female to U.FL Female adapter or cable. I have searched everywhere and can't find one. Without it, this means trying to solder the microscopic connector that I doubt I have the skill to do.

Here is a Male to Female example of what I am looking for:

View attachment 17257

Does anyone have a source for a U.FL Female to U.FL Female adapter or cable?

I attempted to solder a U.FL connector last night. Forget about it! The tip of my iron is 3 times the width of the connector. I don't have great solder skills, do they make specialized solder gear for tiny, tiny work?

10Pcs IPX / U.FL Female to IPX / U.FL Female Coaxial Cable 1.37mm 15cm Wireless

Right description, wrong cable

 

[sprtbkrydr]

I attempted to solder a U.FL connector last night. Forget about it! The tip of my iron is 3 times the width of the connector. I don't have great solder skills, do they make specialized solder gear for tiny, tiny work?


Right description, wrong cable

What would have to be different for it to be the right one? Is one end of it right?

 

[sprtbkrydr]

Is this the right end?

MHF I Ni Top | I-PEX Connectors

 

[beanbubba]

Is this the right end?

MHF I Ni Top | I-PEX Connectors

Need a cable or adapter with this on both ends:

 

[sprtbkrydr]

Need a cable or adapter with this on both ends:

View attachment 17334

So the one above is right then? Sorry for my ignorance I was just trying to find the right thing.