2.4Ghz "Cantenna" wiring - Can waveguides be welded together?

Discussion in 'Wireless & RF Design' started by stuckstick, Oct 16, 2015.

  1. stuckstick

    Thread Starter New Member

    Oct 15, 2015
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    Hello everyone, I am a new member and this is my first post; I do hope it is located correctly, and trust the moderators will adjust as needed.

    First, what a fantastic website! So many resources, shared by people genuinely interested and helpful. :)

    I have NO electical background, have successfully built high performance automotive engines, in particular cylinder heads and specialised in modifying carburetors extensively in a previous life, but... electrically speaking I am about at the level of flaslights and wall switches for household lighting.

    To date I have built some 2.4Ghz "cantennas" that have worked very well. I use these for WiFi around the house and is now my "hobby". My "testing" is nothing more than simple observation ie. did it provide results as expected, and is the signal (observed through computer software such as InSSIDer, Vistumbler and others) steady and without a lot of fluctuations or drop outs - answer "yes" to both criteria.

    Recently I decided to create a pair of waveguide antennas to use with a USB wireless adapter that has two non-removable antennas on it as delivered, the co-axial cables for each soldered directly to the PCB. My plan was to create a waveguide "cantenna" for each existing antenna and solder the new cables the same way to the PCB since I have seen this done succesfully on YT videos. The "cans" are typical food type so were separate from each other, however I wanted to add a "horn" to the front of each can for a bit of added gain and in this case for appearance reasons and this is what had me wondering about the electrical properties that I admit I do not fully understand. The "horns" I opted for were something found in a store and were *already spot welded together* but looked like they would mate nicely to my food cans.

    It's all assembled now, working and painted. In total there are four antennas now because this was to be used at a family members trailer where wifi is available but distant. The goal was to use the directional feature of the cantennas to tx/rx and use the smaller original antennas to distrbute signal around the premises. This is done either with software or within the operating system. The directional feature of my new device seems to work and provide some extra gain but evry so often will drop for a second or two then go back to a fairly steady rate varying only about 1-2dB. Nearby signals NOT aimed at by the cantennas are up and down almost always and vary by about 5-10 dB. This is unlike my other cantennas where signal varied extremely little, near or far.

    I have purchased some USB wireless adapters that were manufactured with two replacable antennas and on those the "ground" (threaded portion of RP-SMA connectors) show electrical continuity on all the ones I tested. Using a pair of replacable cantennas attached with RP-SMA connector on THESE adapters I do not get fluctuations or anything unexpected.

    Since I have this painted and assembled now, and reeeeeeeally don't want to cut and hack if not truly neccessary. I'm trying to get information about "tuning rods" because that will be something I'd like to learn about, is possibly an easy feature to add, and could possibly minimise or eliminate the problem - any suggestions appreciated.

    QUESTION: Does the spot welded "horns" cause an electrical problem and maybe excessive VSWR or other undesirable result, and should they be separated?

    ps - if necessary I can provide specs and a photo but generally this is two "cantennas" with recommended dimensions and materials, the co-ax cable from the cantennas to the PCB is (shamefully) RG-174/U because that's what I have plenty of
     
  2. stuckstick

    Thread Starter New Member

    Oct 15, 2015
    4
    0
    ADDITIONAL INFO:

    Here is a photo of this particular device. I collected the materials many months ago and wanted to finish this, mostly as a "proof of concept" for my own satisfaction. I now use different materials, and wouldn't intentionally fasten the waveguides anyway. The problems Im'having with this are "a learning opportunity" so I'm hoping to resolve the fluctuating signal I did not expect, even with nearby, unobstructed signal source - something's not right.

    For anyone reading this that has experience with such a device; I hastily tested for continuity after soldering the new cables to the PCB and thought both were good, but one was weak and I must have unknowingly broken it during assembly. What I experienced during the first try out was "less" fluctuation and more directional sensitivity - difference of 12-14dBi (InSSIDer v3) when pointed at or away from Tx. Once I reconnected the broken solder (signal) wire overall signal was higher and directional sensitivity was less, but fluctuation was more pronounced, pointing at or away produces 8-12dBi difference.

    I add this because it's possible that my newbie soldering job is at fault. I acknowledge that having two waveguides functional vs. one (when wire broken on first try) will often grab more signal. The fluctuation is my concern since my other waveguides (cantennas) produce strong, flat signal.

    i will try to upload some sreenshots of the signal graphsand anything else I think of.

    IMG_0068sma.jpg
     
  3. SLK001

    Well-Known Member

    Nov 29, 2011
    812
    225
    The two antennas on the Wi-Fi adapter are for diversity. Usually, they are oriented orthogonal to each other, so that maximum coverage is achieved. The wifi chip will sample each signal every second or so, and switch to the strongest signal. Your antenna setup has both antennas with the same boresight, so they are receiving basically the same signal. Also, they are in the sidelobes of each other, which could possibly be the reason for the signal fluctuation.

    Also, your flare is very shallow - you probably gain very little extra with it. To significantly increase the gain, you'll need more angle on the flare. Welding the flare to the waveguide is fine - you are guiding the wave, not conducting it. Below are pictures of my "cantenna" with a flare. This antenna simulates to approximately 17dBi of gain. Using WIRELESS NET GAIN, the signal gain is about 15dB better than the laptop OEM antennas.

    DSCI1712.JPG

    DSCI1711.JPG

    DSCI1713.JPG
     
  4. stuckstick

    Thread Starter New Member

    Oct 15, 2015
    4
    0
    Thanks SLK001 for replying. I left the original antennas as manufactured and their positions are adjustable. For some Tx points having them horizontal does improve signal. But mostly they will be used vertically to share a distant signal acquired by the waveguides. Good point about the side lobes of the waveguides, I am aware they are too close together but the "flares" were originally attached when acquired as you see them now and this was to be a quick prototype thus they remained joined and served as locations for the cans.

    After comparing this unit against others (singles) I have built I find that regarding fluctuations A) aren't really much different than the others, or different from OE adapters, as I originally percieved and B) having options to move the small white antennas and also tilt the waveguides I can nearly eliminate the fluctuations if I spend a few minutes focused on a particular Tx point. Emphasising the improvements are for a specific Tx and don't necessarily improve for all points; each would have it's own sweet spot that needs to be determined individually. Since the photos were taken I added "tuning stubs". Those easily make some change but since the dimensions were already spot on and they were placed directly over the active element vs. say a 45 degree angle, it's extremely sensitive very easy to "go past" the ideal, again a prototype or proof of concept thing.

    I wholly agree regarding the angle of the flares, again this is how they were acquired and at that time I didn't have much other materials. In future I will experiment. I keep reading about the 30 degree angle but there is so much incorrect and incomplete information on the internet I will verify on my own I guess. For example some people suggest 30 inclusive (15 each side of the centerline), some say 30 each side of centerline, some say anywhere between 30 and 45 from centerline... I think anyone can agree that just about everything "matters" regarding an antenna and many home built ones are mostly a result of available materials, retained or gleaned information, and amount of time, patience, and commitment applied.

    Is "WIRELESS NET GAIN" a software you are using? I couldn't find any such using that as a search query, I am looking for a (current) software that displays two colors to show signal vs. noise.

    It appears from your photos that you are using a cone type element, and it looks to be copper - is that correct or is it brass? I am curious about it's dimensions. It also appears that you used F type connectors, if that is correct do you think there may be any impedance issues ie. not 50 ohms? That leads me to ask about the coaxial used, is it RG6 or something else? Any impedance concerns? Obviously you are getting noticable benefits, but I raise the impedance matter because I wonder if the numbers are partially due to VSWR which is typically high on "cantennas" anyway, as far as I know.

    I apologise for the lengthy reply, I did want to address your much appreciated comments. My original question was about welding of flares, not so much about the flare to the waveguide but about to each other as seen in the photo. Yours apppear to be spot welded and I have no doubt they work, my concern was about any interference, cancellation, VSWR etc - only a prototype but I hate to waste and wanted to learn something. Since mine is a "double" I think any issues may be spacing (side lobes as you mentioned) and I would not repeat this design. But I'm beginning to think that since so many dual antennas, including 2.4GHz/5.8GHz dual type, are commonly grounded that I will be okay, electrically speaking, with this unit. I value your opinion on that if you have anything to add.

    I'm also beginning to think that the fluctuations I didn't expect are due, partly at least, to this unit having less gain than my other single waveguide units. Those are built quite differently and use different materials. Therefore this unit may not be able to lock onto a signal quite as well, may suffer a bit and that shows as fluctuations?

    SLK001 thanks for sharing your photos, results and suggestions.
     
  5. SLK001

    Well-Known Member

    Nov 29, 2011
    812
    225
    Actually, the program that I use is called "Wireless Net View". If it loads properly here, I have attached it in .ZIP format. All my connections are done using SMA connectors (50 ohm) and RG-59 (?) cable. I made my antenna feed from sheet copper - not sure what the dimensions are - was done over 9 years ago. I used data from an IEEE paper to get the design criteria, but I can't seem to find it now. I get about 1 to 2 dB extra gain with the cone vs a stub feed. As for your fluctuations, your dual antennas may be interfering with each other, or your AP may be using "Smart Power" and reducing output power if it detects a good enough S/N ratio. With the AP using spread-spectrum to broadcast, some amount of fluctuation is to be expected, since the receiving chip is using a simple RF detector to determine the S/N ratio instead of the real DATA/NOISE ratio (or Bit Error Rate). Also, a lot of receiving chips do not report the NOISE level, so arbitrary values of -99 or -100 dB are used.

    As for your setup, I would get rid of one of the cantennas. With them both pointed at the AP, they will probably be jumping from one to the other, and back again continuously. Depending on the criteria for antenna switching, this could be giving your receiving chip an identity complex in not knowing which antenna to support, thus trying to support both!
     
  6. stuckstick

    Thread Starter New Member

    Oct 15, 2015
    4
    0
    Thank you! It downloaded from here just fine. I just copied the name used above and when I saw the word "gain" I thought I should ask about it since the only program I know of that shows bar graphs in two colors (signal, noise) is old and doesn't work with most newer wireless chipsets.

    The RG59 coaxial and the F Type connectors to the active element are 75 ohm as far as I know, many people have built projects using it and had success. I asked because few projects I have seen take the time and effort to produce a cone type element and a properly sized flare or horn and I was curious about the effect of impedance and/or VSWR on such a nice project and whether any issuing extra impedance above 50 ohms would be part of the extra gain numbers. Good to hear a number (extra gain) associated with the cone element - every bit counts.

    Typically I read about cone elements and wherever the dimensions are suggested they are given as about 6mm diameter and 24mm height tapered to about 1mm at the base. Never seen any "science" to go with those dimensions but that is typically what is uggested.

    This adapter only has about four parameters that can be changed, one of which is "Antenna Diversity" and the options are 1, 2, or 3. I cannot find any OE documentation explaining the difference or what to expect from changing. I have a rough idea of the concept and I do see your point about the cantennas being too close and a possible cause for the fluctuations. Even before I added the waveguides I experimented with the settings and couldn't discern any difference, either in software or 'seat of the pants' observation. I also thought beforehand that the two so close was not ideal but at this point I can't see taking it all apart since I use different componets now for future builds. Perhaps I'll have another go at the diversity paramter settings now.

    My original idea was to find a USB adpter that had external antenna(s) of some kind, then add waveguides with the purpose being (besides fun) to use in summer where the access point is some 600' away l.o.s. and share the connection nearby as opposed to just being USB wired to one computer only and so I thought the small antennas would serve a purpose. Also, this kind of adapter typically has 300mbps bandwidth when equipped with two antennas and the matching chipset vs. 150mbps with one antenna, more bandwidth being desirable for my sharing purposes.

    When I did have only one waveguide functioning (my broken solder connection above) it worked well and was more "directional" than with two. With two good connections the peak signal was not appreciably higher but the "valleys" of the signal graph were definitely higher, so I'm thinking that more area "under the curve" is of benefit bandwidth-wise. Again, good for sharing purposes. Directionality was less with two than with one.

    The cantennas are soldered to the same two points as the original antennas of course, and as the small originals are originally spaced about 2" apart and advertised as "high gain" I will probably leave them. I probably won't delete one cantenna since that will cost time and paint and probaly can't be done gracefully and I'm pretty well finished with this build. What are your thoughts regarding desoldering one of the connections on the board and attaching it to the remaining connection ie. one antenna connection on the board would then be fed by two waveguides and one original pivoting white antenna, the other just by a single short antenna? This way, because as you say, the two waveguides are so close and focused at the same point the chipset would see signal closer to what the designers anticipated.
     
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