Archer C7 1750 V5 antenna modding?

#1

Hey so I've been looking to mod a C7 V5.X. Detachable antennas are pretty rudimentary to install due to the internal connectors being just UFL. Swap those out, put in a nice set of RP-SMAs, grind out some plastic and we're good to go. I'd like to ask about the 2.4G/5G layout tho. How is that handled and which antennas do which? On that note, does the V5 have traces for the internal antennas or are those only present on V1-V3? It'd be nice if I could put some UFLs on those and compile with a custom patch.

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#2

The antennas are dual band. It is 3x3 MIMO on both bands. There is a chip diplexer for each antenna combining the two bands right next to the U.FL connector.

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#3

So I could potentially split the antennas if I tap before the diplexer? Or is the chip doing more than just multiplexing

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#4

The diplexer is the little white chip outside the RF box. It's a passive filter that doesn't do anything other than combine the signals from two radios to one antenna. You could potentially modify the board to tap the signal before it reaches the diplexer, but that would not be simple.

Do you have the unit now or were you thinking of buying one? In the latter case you should look for a model that already has separate antennas for each band, it will be much simpler to hook up single-band antennas to that.

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#5

I already own it. I have a fair share of hardware modding experience so I might give it a try. Need to inspect how small things really are first.

Thanks for the information!

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#6

might be of interest to you how i did it with c7 v1

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#7

Looks clean. I'll likely mount mine in the front or sides, since I'm wall mounting the entire machine and want to have a flat profile

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#8

Regulatory warning: Meraki MR16 antenna connectors
Warning you may not get what you desire: Meraki MR16 antenna connectors

I hope the best in your experiment.

@psyborg, your pics aren't showing up on my end. Odd, I have to actually go to the image's link to see it.

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#9

Just remember that wires don’t behave much like wires anymore at 2.3 GHz, even more un-wire-like at 5 GHz

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#10

updated to include embed links, again, while trying to put image forum complained that it must be smaller than 4096KB, and images had about 1200KB so i used web upload from zippy but seems like they change url to prevent hotlinking.

@jeff can you explain that a bit further? while his version has dual-band ones, i was able to confirm v1 are 5GHz only. putting these to 2.4 gave lower signal strength than regular 2.4 antennas that come with alfa usb cards.

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#11

Once you're above a few MHz, and certainly by the time you're in the GHz range, wires no longer have the same voltage on both ends, even when taking into account resistive losses. They start to look like inductors, capacitors, all coupled to anything and everything around them. A piece of coax is the shape, size, and material that it is mainly because it matches 50Ω (or whatever the characteristic impedance of the line is) source and load impedances, without "bouncing back" energy. Similarly, that trace on the PC board, its width, the material of the board, the ground plane beneath it, all ensure that its impedance matches the components at either end.

Off by a little bit, you lose power. With a 3:1 SWR, you lose 25% of your power. Both that and feed line losses could easily swamp any gains an external antenna might get you. Here's a typical "commercial quality" pigtail https://www.mouser.com/datasheet/2/398/CAB.622-1218656.pdf

At 2.5 GHz, assuming everything is perfectly matched, you lose ~1dB of power. At 5 GHz, it will be ~2 dB,

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#12

(@jeff, I [and others who studied radio theroy] are gonna say...if you have to ask DON'T DO IT)

EDIT: you also have to consider what's called balance or imbalance, that's why that other post (and this is pseudo-jargon)

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#13

I'm a beginner radio/ee/software engineering student. The implications of having an extended line from the diplexer didnt come to me. Granted I've had my fair share studying coax, I know what you mean. Guess that splitting the antennas isnt something that will provide any real benefit.
Brings me to another question about the 2.4 antennas. Those have U.FL connectors on the board. If I want to mod it to have RP-SMA and have approximately the same lenght cables how much of an impact would that have on performance, if any noticeable?

Also about your post in the other thread, doubt a cheapo 12V $50 router has the power to cause any harm to a human. Good general warning when working with high power equipment tho.

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#14

Good question...for specific answers, you can check the loss measurements for those connectors. The manufacturer should know. Connectors are also rated for certain frequency ranges. At the time of my posting, I can't recall what ranges for RP-SMA...but I'm almost certain it's rated up to 18 GHz.

If you connect it to a directional antenna...or amplifier...but yes, I get your point. :grin:

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#15

It's not the connector that is going to cause you problems, but that the footprint for a u.FL and a PCB-mount RP-SMA are not the same. Remember, those are impedance-matched strip lines, not "wires" on the PCB.

If you want RP-SMA, you'd likely be a lot better off with an u.FL / RP-SMA pigtail.

If I were to guess as to the losses that would be introduced by slapping an RP-SMA connector on a u.FL pad, I'd guess 3 dB if you're lucky, 6-10 dB more likely. It's a guess because "nobody" does that at these frequencies, especially if they have the roughly $10,000 device needed to measure the losses.

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#16

@jeff makes an excellent point.

To actually test full loss, you have to retest the entire radio system... with the new antenna system included. This is where the regulations I mentioned come into play; as in most countries, only the manufacturer is legally allowed to alter this - and only in the device's production phase.

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#17

Yes that's what I meant. Would the pigtails impact performance in any significant way, asuming they're the same lenght as the originals

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#18

Assuming you purchase quality pigtails (which is unlikely through the various "import" sites), the loss of one 10 cm pigtail is probably comparable to another 10 cm pigtail. There will be some additional loss due to the additional connector and its mate itself. Based on top-quality connectors, such as https://www.amphenolrf.com/connectors/sma.html, you're probably looking at ~0.05 dB per connector (you've arguably got two including the one on the antenna). Non-spec ("cheap") connectors, you're on own.

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#19

Recommendations for high quality pigtail sellers. Preferably ones in Europe.

Thanks for all the info btw

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#20

Any of the reputable component houses. As one place to get a list https://www.sierrawireless.com/distributor-page/#/r=EMEA and look at their "Premier Partners".

I've purchased Taoglas pigtails through Mouser here in the US as they have "real" spec sheets and they seem well made. There is a significant difference in loss between the 1.1 mm and 1.3 mm cable, with the larger cable significantly better.

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