RX amp required - NOT TX


I know I am in a minority here, but I don't want to increase my transmitter gain - if anything I tend to back it off a little. What I am trying so hard to find is an inline device which offers perhaps 9-12 dB gain for the receiver and (possibly) 3dB gain for the transmitter just to get rid of the insertion loss. Ideally I want a unity gain for the transmitter side after insertion of the RX amp.

To keep myself busy, I install Hotspots and although I have tried a selection of makes over time, the most common problem is that the laptop client can see the AP but the AP is deaf to them. As it is I use moderate gain aerials (about 8dB) and usually limit the TX power to around 50mW. This as a rule tends to mean that MOST clients that can see the AP can also be SEEN by the AP.

I don't see the point in bellowing out hundreds of milliwatts when the client is whispering back with perhaps 30, of which 20 is going into their thigh.

Already googled myself senseless and checked Ebay repeatedly. The only time I can find a pre-amp for the receiver it is almost an afterthought for some gizmo that will pump out 500mW - 1500mW and as an afterthought, increase the RX gain by perhaps 6dB

So far the only thing I can think of, is to buy one with a decent RX gain - ignore the transmitter gain totally and then just under-drive the unit so that AFTER the transmitter has been amplified it is still only pumping out around 50 - 80mW - but in the process has some 6 - 9dB gain for the receiver.

Please - I cannot be alone in wanting to improve the receiver sensitivity more than the transmitter "oomph" - has anyone found a product suitable yet?

Kind Regards


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The wonders of not checking to see if house guest has logged out of her account.

If someone can please give thoughts to message anyway - and if you know of an RX-only amplifier please od let me know either on here or if you prefer, by email.

If you reply by email, please change the "exmarc" to "exmark" for anti-spam.

Kind regards


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I'm pretty ignorant on such things, but have you considered using different antennas to achieve your goal? What exactly is a "moderate gain aerials (about 8dB)"? Is that an omni?

Reply to
Char Jackson

Ugh... That's not going to be easy. It sounds like you want a T/R switch built into an inline amplifier. Those are either keyed by the TX RF, or have a wire running to the AP. The gain of the TX amp is usually not fixed to some number and is controlled by an ALC (automatic level control). This is a strange beast indeed.

Good thinking. If you can hear it, you can talk to it. 8dBi seems a bit high for an indoor antenna, but might work as the signal bounces around off the walls. It's still better than an omni.

Try about 20mw for many PDA's and cell phones.

Well, there's a reason that the RX gain is so low. It's purpose is NOT to improve the receiver sensitivity. The GaAs FET front end of most access points is fairly close to the limit of what can be done with receivers. The best the RX amp can do is compensate for the coax cable and connector losses. Add too much gain, and the dynamic range of the receiver is reduced by the amount of the gain increase. The noise floor remains the same, while the overload point drops with the gain increase. Put a proper 20dB gain RX amp on a typical low power AP front end, and all you'll see is intermod and blocking problems.

Maybe. If you really want more RX gain, without affecting the xmitter, dive into your unspecified model favorite access point, break the T/R switch chip, and bring the xmitter and receiver cables out to separate connectors. Might as well send some DC (through a 2.4Ghz choke) to the RX amp for powering it. The xmitter goes to one antenna connector, while the TX amp goes to the other. Of course, this requires two antennas, but those are cheap and easy.

You could also just break the trace between the T/R switch and the receiver front end, to insert the RX amp, but that would not help to reduce the effects of your unspecified length of coax cable.

I don't think you're going to improve receiver sensitivity much with an external amplifier and certainly not without trashing the dynamic range. I like numbers. What manner of receiver sensitivity were you expecting for a 10% PER (packet error rate). Do you have suitable test equipment needed to measure the before and after sensitivity? That's not a rhetorical question as you won't really know if the additional amplifier is doing any good without measurements.

You don't really need the expensive test equipment as most of the setup can be faked using client radios and AP's as a test generator and receiver.

Question: What problem are you trying to solve by adding an RX amp? Reducing coax loss is a solution, not a problem that needs solving. Are you having reliability, coverage, thruput, interference, multipath, or other problems at your hotspots?

Reply to
Jeff Liebermann

Argh. After typing out a somewhat verbose but numbers rich reply my PC decided to reboot without warning - thankyou Avira, that was most kind.

To give a slightly more condensed answer :) :-

Reliability is not an issue for some users - eg: almost any Dell computer seems to be able to get a reliable connection even if they see us around -70 dBm - On the other hand Advent / MSI computers can fail to make a decent connection even if they see us with a strength of -50dBm.

Coverage is fine with some clients - again Dells, or any decent spec USB devices - which tend to throw out a bit more power than some of the the notebooks do.

Throughput is fine - is someone can connect to us, they often can pull data as fast as we can hoover it out the cable connection to give them.

Interference - well there are no shortage of other users about - but it is consistently the case that borderline users can always see us, but just cannot shout back loud enough for us to hear them.

As for multipath, I am guessing with MIMO that ought not be a problem - though I admit if it is, I am unaware of it.

The problems are largely solved if we disable the onboard AP and drive any of the ubiqitti AP's from the public lan port. For some reason Ubiqitti radios (especially the NS2) have a fantasically high sensitivity and while fully appreciating your comments about saturation / SNR etc with over amplifying, the sensitivity of the receivers on NS2 is I think in the order of -95 to -97 dBm. Certainly they are the most effective units we have EVER found when it comes to connecting weak clients (talking more about specific applications over a distance here not hotspot)

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To be honest, although I am not adverse to playing around with transceivers, once they get into UHF (and high end of UHF too), it has gone way past my skills to make neat cuts / connections etc on PCB's where an extra 1mm of track in the wrong place can suddenly make the whole thing go downhill in terms of performance.

Give me something working at a few Megs and I will tinker all day :)

I think I was just hoping someone would come back and say something like "You need the RX+12 from whizzlec for about £25" - alas they didn't :) I think the simplest answer is to stick with the NS2 solution. It seems wasteful but it DOES work and it IS simple.

Thanks again though for your helpful and throughtful comments and questions - I apologise for just giving a condensed version of my reply as the figures I pulled from the Xirrus Wi-Fi inspector for example evaporated with the reset and I am just a shade too tired to go outside and take readings again now!

Kind Regards


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Ummm.... that's often an early symptom of the dreaded bad Low-ESR electrolytic capacitors on the motherboard or power supply problem. See:

Open the case, blow out the dust, and inspect the caps.

Ummm.... I would hate to see the size of the original.

You're not going to solve that with a receiver amp. The problem is that most (not all) wireless client software is fairly smart about listing only those access points where it has a good chance of connecting. The usual criteria is surviving the 4 way initial 802.11 association and handshake. The problem is that network sniffers, such as Netstumbler, Kismet, NetSurveyor, WiFiHopper, ad nausium, only listen for responses to network probe packets and broadcasts. They will display "alligators" (that's a radio with a big mouth, and small ears) that there would be no hope of ever connecting and using.

I got a good demonstration of that today while sitting in the dentists office. My iPhone 3G would see only 1 secured network. That wasn't going to work. So, I fired up yFyLite (Netstumbler clone) and found about 6 assorted networks, some showing rather substantial signal strengths. I recognized the MAC addresses of 2 of the strongest as Cisco and Sonicwall, two of the leaders in the "more power is better" wars. I tried to force a connection to the strongest, but the iPhone would not connect because the AP was deaf and couldn't hear me. Duz this sound familiar?

You didn't really answer my question. What problem are you trying to solve? If it's the difference between a network sniffer and what a wireless connection manager shows, forget about RX amps. It isn't going to make much difference.

Ummm... Most laptops use MiniPCI or PCIe Mini cards. Although there are some high power varieties, most of the commodity variety belch somewhere between 50-100 mw. Same with most (not all) access points. What's different between "good" and "marginal" laptops and access points are the feed lines and antennas. Many antennas barely work such as this old Compaq mounted on the hinges:

Others have 2ft of high loss small diameter coax as a feed. Still others use antennas that should never have seen the light of day. I've disconnected the connectors on a laptop and temporarily attached a pair of decent air dielectric PIFA test antennas, and seen spectacular improvements in performance.

Another problem is buggy software. I'm always amazed at the often radical differences in performance I've seen when I upgrade the wireless firmware and/or drivers.

Thruput may be fine, but what about error rate. You can't tell if half your packets are getting trashed (for various reasons) using a simple thruput test.

Why would you want other "users" (presumably client radios) to hear you (presumably another client radio)? Are you doing Peer to Peer? Please avoid the ambiguous terms "us" and "them".

MIMO is all about speed, not reliability. Multipath performance is required for spatial diversity MIMO to operate, but all you get is more speed, not more reliability. In this case, if the MIMO access point can't hear the client radio, the AP will switch down to 802.11g speeds. More simply, it takes a good strong signal for MIMO to work well.

I just hate agreeing with you, but Ubiquity stuff works well (and is cheap). I recently replaced some WAP54G v3 pieces of junk with Ubnt Bullet2 radios. It was a major improvement. However, I won't say anything nice about their non-802.3af PoE injector. Retch.

If I can get chain saws, Coleman lantern, and friends HF SSB radio off my workbench, I think I have everything I need to do a proper sensitivity and dynamic range bench test on some of the radios I have in stock. It would be interesting to see what Ubnt does differently (such as an external RX RF amp on the PCB, lower loss BPF, or lower loss T/R and diversity switches.

Ummm... careful when you read the data sheets. Everyone lies except amazingly Dlink. The RX sensitivity numbers are invariably direct copies of the chipset sensitivity from the Broadcom or Atheros data sheets. In the distant past, I started researching the numbers and produced a spreadsheet and graph demonstrating the hype:

The Dlink numbers are real measurements. Also note that the numbers for the Ubnt Lighstation is about 3dB better than any of the other units, which makes me wonder what they're doing.

I now use a surgeons binocular glasses and a microscope. It's actually easier to work with microwaves because the components actually work. It's not like 220Mhz, where all the leaded components have enough lead inductance and irritating self-resonances, to render them useless.

Sure. Then you can battle exactly the same dynamic range problem at HF frequencies, with the added enjoyment of dealing with atmospheric noise levels well above your receiver sensitivity. I'll take microwave any day over designing 100dB dynamic range power burning RX front ends.

Actually, there are plenty of 2.4Ghz RX only amps available. Before I waste my time supplying a list, tell me where in your unspecified access point you are going to install it?

Y'er welcome. I'm trying to concentrate on anything except myself. The anesthetic from the dentist drilling holes in my teeth and in my bank account is starting to wear off. I'm waiting for the Vicadin to kick in. I never could make the Xirrus Wi-Fi inspector work for me, probably because some of the other tools I use install "shims" in the network stack that mangle other drivers.

I'll try it again...

Reply to
Jeff Liebermann

Try NetSurveyor instead:

Reply to
Jeff Liebermann

But that's useful for a "site survey" thing, where you want to know what's going on in your neighborhood.

[I just bought an Engenius EOC1650 to get wifi into the back rooms of our house, and (bonus) into our backyard. It comes with a "scan" feature, but I dug out my ancient iPod Touch and loaded Stumbler into it, and it's way more sensitive. Hey, no one around me is using channel 11, so there I boldly went with that fine AP. My Dlink main router uses channel 1, along with my neighbor, but we've not had problems.]
Reply to
Prinzip Gavrilo

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