Forum Discussion

rwbradley's avatar
rwbradley
Explorer
May 18, 2015

Install WIFI antenna on Batwing Mod

I decided to mount a WIFI antenna for those few times when WIFI actually works for me.

What I had:
- WIFI Antenna with N connector
- RG58 cable
- old Linksys WRT54G router running DDWRT configured as a Universal Wireless Repeater to repeat WIFI from campground to Router and than my devices connect to it using my SSID
- aluminum bracket from old network rack mount hardware
- flame retardant conduit putty

What I needed:
- LAP sealant

I decided the best way to do a permanent setup was to use a shelf beside the fridge to put the router on that shelf and run the cable out the side of the shelf into the void behind the fridge to get to the roof. (while I was at it I installed a Wilson Sleek too, separate write up)

1) remove fridge vent cover
2) cut enough of the screen to allow the cable to pass thru
3) drop cable down into fridge vent void
4) cut hole in side of shelf to fridge vent with a spade drill bit
5) fish cable into cabinet using a pull rod (coat hanger would also do)
6) drill hole in bracket to fit N connector thru it
7) use 2 sided tape, bracket and tie straps to mount antenna on Batwing
8) reinstall fridge vent cover
9) cover fridge vent screws, and along the antenna wire with LAP sealant

I found afterward that I had to shave some off the edge of the bracket so it would not hit the antenna head as it came down. That was easy to do with a metal file since I used an aluminum bracket







Moderator edit to re-size pictures to forum recommended limit of 640px maximum width.

  • SCVJeff's avatar
    SCVJeff
    Explorer
    May 18, 2015
    Here's mine.
    Hopefully you are using the term 'RG-58' as a generic, because it's loss at 2.5GHz is close to 40db per hundred feet, as opposed to LMR-200, almost the exact same size @ ~16db for the same length. That's a huge difference, even at 10'.

    Also from the school of been there, go to Home Depot, Lowes, or Harbor Freight and replace those zip-ties with Stainless zip-ties.


  • rwbradley's avatar
    rwbradley
    Explorer
    May 18, 2015
    Definitely used RG58, would have gone higher but I did not want a hole the size of my arm in the trailer. Also I measured out the length exactly. I think I ended up with about 1-2" extra.

    Never seen stainless zip ties, I will check it out. I just figured on replacing these ones every year as the sun makes the plastic brittle.
  • Tom_M1's avatar
    Tom_M1
    Explorer
    May 18, 2015
    If your WiFi adapter is USB, you could move it closer to the antenna and run a long USB cable. You can go up to 16 feet with a passive cable, 100's of feet with an active. This would minimize your RF loss.

    As Jeff noted, your zip-ties will self destruct in a matter of months from UV exposure. At the very least get some black nylon ones which are UV resistant.

    While you are on your roof replacing zip-ties, you might want to move the antenna up higher on the mast.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    May 18, 2015
    I do believe they are exactly the same size for the good stuff, and yours looks like it is. The difference between the two is .048mm, but the difference in performance is HUGE.

    Below are the cut sheets for LMR-200, and Belden 9201, considered a reasonably good RG-58, and there are many.

    LMR-200

    Belden 9201
  • Oldme's avatar
    Oldme
    Explorer
    May 18, 2015
    RW....Nice install.
    While everyone talks numbers on all communication cable,
    in real life a run as short as yours would show no real
    loss or improvement. Being a short run is the key here.
  • tahiti16's avatar
    tahiti16
    Explorer
    May 20, 2015
    Short is absolutely a critical but with the huge difference in loss between the 2 cables I would opt for the lower loss. Remember we are trying to "fix" a weak signal and the cable we are talking about is before any amplification.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    May 21, 2015
    Oldme wrote:
    RW....Nice install.
    While everyone talks numbers on all communication cable,
    in real life a run as short as yours would show no real
    loss or improvement. Being a short run is the key here.
    Loss is loss no matter how you slice it, and if you have the RF background to make that statement you should know that.

    I ran this out when the OP posted this with generic hi-end RG-58, and it works out to roughly 3.6db @ 10', and his run has to be very close if not exceeding that. That's less than 1/2 the power to the antenna. Don't tell people that's not significant.
  • rwbradley's avatar
    rwbradley
    Explorer
    May 21, 2015
    tahiti16 wrote:
    Short is absolutely a critical but with the huge difference in loss between the 2 cables I would opt for the lower loss. Remember we are trying to "fix" a weak signal and the cable we are talking about is before any amplification.

    That is the point that many people seem to miss. In theory most Omni antenna's are only able to add up to 8db of gain (despite what the packaging may say), with most in the 2-5db gain. Cable loss is so high in some cases it can be as much as about 1db per foot for really cheap crappy cable. This tends to defy most peoples understanding of antenna theory. Ya an antenna on a 100ft pole would be great, your line of sight would be fantastic. The problem is that you would gain 8db from the antenna, but may loose 20-30db from cable loss, putting you way in the hole. Also joining cables adds additional issues to because of connetors, a pair of 5ft cables connected together will loose about 1db additional vs a single 10ft cable.

    My antenna was an 8db antenna, I figured with the RG58 at the length I choose, I would loose about 2-3db. When I tested, I was seeing +5db vs without it, exactly what I expected.

    My opinion is that as long as you get it outside the trailer and up above the roof line, this is your best case scenario, as if you plan the placement of the router and the antenna carefully, you may only need 2-4ft of cable to do it and if you use RG58 or better you will only loose a few db from the cable. This will deal with line of sight/obstruction issues, faraday cage issues from the trailer itself, and cable length issues.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    May 21, 2015
    It's 3' just to get to the top of the mast, ~2' on the roof, and from the pix it appears another 2-3' inside the cabinet mebbe. That's why I picked 10' for the comparisons.

    EDIT: I just went back and looked at the RG-58 data sheet above, and 2.5GHZ isn't even listed (clearly not the one I thought it was).

    So the best that one can take from this is the losses shown at 1000MHz
  • rwbradley's avatar
    rwbradley
    Explorer
    May 21, 2015
    To clarify since I did not mention it anywhere, because I wanted to be on the Batwing, I used 2M (6ft) of RG58 and it was close (only a few inches to spare). But my last comment was just illustrating an option. Surface mounting to the roof could get you down as low as 2-4ft, but mounting on the Batwing may take about 6-10ft depending on the layout. Both options would keep your loss at an acceptable level if you used RG58 or LMR200 or better and would deal with the Faraday cage and line of sight issues, it just depends on personal preference or layout/mounting options.

    I also was not able to find a chart for above 1000mhz either, so I just estimated based on about -1.5db at 1000mhz for 6ft, I would likely be in the -2-3db at 2.4ghz. Since my tests were just informal using the db readings my router was giving me, I figured my numbers were good but far from exact science.

    In the end I am happy with the install, and I have retested several times and continue to replicate about +5db with the external antenna on vs using the stock antenna.

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