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Thread: best antenna

  1. #2271
    First officer 1090 MHz's Avatar
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    Quote Originally Posted by JLD View Post
    I don't know if your friend has measured the return loss but if the antenna works well, it probably means that the decoupling sleeve is effective and the cable between receiver and antenna does not radiate much.

    One question: what did you use to adapt the decoupling sleeve to the brass tube?

    JL
    Since a DME system also transmits a signal, it passed that tx signal test too. The radome (casing) connector and sleeve balun were taken from a 2.4 GHz Wi-Fi antenna. I re-tuned the balun using some 1/2 inch copper water pipe. http://ads-b.ca/antenna-collinear-F-CYYZ2/img_9719.htm

    This is the DME I was trying to copy: http://upload.wikimedia.org/wikipedi...px-DME_SGT.jpg

    An airplane’s DME interrogator uses frequencies from 1025 to 1150 MHz. DME transponders transmit on a channel in the 962 to 1213 MHz range and receive on a corresponding channel between 1025 to 1150 MHz

  2. #2272
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    Quote Originally Posted by JLD View Post
    Well, started to search where to find corrugated coax in EU but does not seem easy!
    Any input is appreciated!
    Re: source of corrugated cable

    Firstly, thank-you to 1090 MHz for the Super Antenna concept and close-up photographs, which served as inspiration to attempt a similar build.

    After being unable to find a local source of LDF1-50 cable, and not wanting to incur shipping costs on what could be a bulky and heavy package, last summer I visited a couple of metal recycling companies (scrap yards) Apparently, with the continuous changes in cell-phone and radio technology, there are lots of new radio antennas being installed, and old ones being decommissioned including the removal or replacement of the cables. With the high value of copper, the premium coax cables used in cell phone and other communication towers are in high demand for recycling, and as a result, the scrap yards have lots of coax of various types, diameters and lengths. I can only imagine that the same would be true in Europe

    While unable to find any LDF1-50, a couple of visits to the scrap yards produced a variety of lengths of FSJ1-50 in good condition, ranging from 10 to 20 feet each, along with some of the larger LDF4-50. Other than a slight difference in velocity factor, the big difference between the LDF and FSJ families appears to be the corrugation, with LDF being ringed and FSJ being spiral. (Each has its advantages but both are very high quality low loss cables.)

    Scrap metal, including coax, is typically bought and sold by weight, and for a low cost per pound, an experimenter can acquire a lifetime supply of high quality cable at low cost.

    I'll report on my build and results after the snow clears and I can get the antenna onto the roof. So far, I'm pleased with the indoor results.

  3. #2273
    Captain abcd567's Avatar
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    FOR BEGINNERS:
    WANT AN EASY-TO-MAKE INDOOR ANTENNA,
    BETTER THAN DONGLE's STOCK ANTENNA?



    The main disadvantages of stock antenna supplied with DVB-T USB Dongle are:
    (1) It has a very short lead. Due to this, in most cases the antenna cannot be placed at an optimum location.
    (2) The stock antenna is not optimized for 1090 Mhz.


    The short cable length can be overcome by connecting a MCX to F pigtail to the DVB-T USB Dongle, and connecting to the pigtail, the required length of commonly available RG6 cable with a DIY antenna at other end of RG6 cable.

    The non optimized antenna can be replaced by a DIY antenna which has a ¼ wavelength vertical whip connected to core of coax cable, and a ground plane connected to shield of coax. The ground plane can be formed by a disc, a number of horizontal radials, a number of slanting radials, or a food/drink can.


    Here comes the Platenna

    The indoor antenna shown below is very easy to make without any special tools or special parts. It uses a pie plate made of aluminum foil as ground plane (disc), a 68mm (finished length) whip made of core of coax, and a cheap & readily available coax F-type barrel connector with nut & washers.





    Maximum Range Achieved: 250 nm
    Range Rings are 50 nm apart. Outermost ring is 300nm radius





    HOW TO MAKE:

    1. Collect the Stuff
    (1) MCX to F type pigtail for connection of RG6 cable to DVB-T USB Dongle.
    (2) Few meters of RG6 Coax for connection between Antenna & Pigtail/DVB-T USB Receiver
    (3) One F-type Coax cable connector with nut & 2 washers.


    Tip:
    (a) For RG6 coax lengths in excess of 5m/15ft, coax attenuation will be high, and an amplifier may become necessary.
    (b) Even with short lengths of Coax, use of amplifier increases plane count & range.
    (c) the coax connector can be either barrel type or panel mount type (see last photo below)




    F-type Cable Connector (Barrel Connector) with nut & washers.


    Large Size Aluminum Foil Pie Plate



    2. Assemble the Platenna
    The whip at top is ¼ wavelength (68mm)









    Dimensions of Whip
    Any one of the two connectors shown below is ok
    Last edited by abcd567; 2015-03-14 at 19:29.

  4. #2274
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    I set up a raspberry pi to receive ADS-B signals in my loft last week, and initially used the supplied magmount whip, trimmed to 1/4 wave and sitting on a small cake tin. This worked OK, but unsurprisingly the performance was a bit lacking. Maximum range was around 50-60 miles with the majority of contacts occurring much closer than that. Since I didn't have much in the way of materials laying around, I decided to fabricate the most basic antenna with what I had to hand - a short cable modem patch lead. I cut one connector off and stripped the braid back exposing the central core to 1/4 wavelength, and formed the braid into 4 radials to act as a crude ground plane. After connecting it, I found that reception was less than stellar. I then remembered that I had a surplus satellite diplexer, which could act as a high pass filter. Installing that made a big difference. Here are the results:

    antenna change.PNG

    Can you guess what time I installed the new antenna yesterday?

    So the overall results are that number of positions recorded over 24 hours increased from about 95,000 to 232,000 and maximum range increased to around 130 miles. Not bad for less than £5 in parts and 20 minutes fiddling.

    Going to try a few of the other antenna designs described here next to see if I can improve it further.

  5. #2275
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    Took me more time than expected to make some trial with co-linear.
    I made one using 8mm brass tube and TV coaxial cable with a measured VF of 0.82 (removed the braid of the cable and inserted inside the brass tube).
    I also used a decoupling sleeve at the bottom, made of 16mm copper tube.
    I made it 8 half wave long.

    It works very well but what I could confirm was:
    - bandwidth is narrow and you need to cut the half waves down to 1 mm accuracy to get good results. Even if SWR can be maintained low over 10 or 20 Mhz, what really matters is the return loss which is much narrower. This probably has the most effect on distortion of the radiation pattern.
    - the adjustment of the decoupling sleeve is critical to make sure SWR is minimal and return loss maximum at 1090. This is the only way to make sure cable and supports don't alter radiation pattern. I started with the sleeve in the theoretical position and was getting average antenna range. By lowering the sleeve 5-8mm to maximize return loss on 1090 (from 15 dB initially to almost 30 dB), the range more than doubled!)
    - I could only make this antenna work well because I have a VNA

  6. #2276
    Captain abcd567's Avatar
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    Quote Originally Posted by JLD View Post
    Took me more time than expected to make some trial with co-linear.
    I made one using 8mm brass tube and TV coaxial cable with a measured VF of 0.82 (removed the braid of the cable and inserted inside the brass tube).
    I also used a decoupling sleeve at the bottom, made of 16mm copper tube.
    I made it 8 half wave long.

    It works very well but what I could confirm was:
    - bandwidth is narrow and you need to cut the half waves down to 1 mm accuracy to get good results. Even if SWR can be maintained low over 10 or 20 Mhz, what really matters is the return loss which is much narrower. This probably has the most effect on distortion of the radiation pattern.
    - the adjustment of the decoupling sleeve is critical to make sure SWR is minimal and return loss maximum at 1090. This is the only way to make sure cable and supports don't alter radiation pattern. I started with the sleeve in the theoretical position and was getting average antenna range. By lowering the sleeve 5-8mm to maximize return loss on 1090 (from 15 dB initially to almost 30 dB), the range more than doubled!)
    - I could only make this antenna work well because I have a VNA
    Good Work!! Congratulations
    It will be helpful for all forum members if you post your antenna's pictures & sketches with dimensions and practical tips on how to make.

  7. #2277
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    Been a while, just getting back regarding replacement coco over spidertenna. Changeover back to spidertenna and within half an hour, range out to double.
    Been working away and not had time to changeover or report but has lead to a good benchmark for me.
    Spidertenna = double distance plus
    thanks
    TYBSU3

  8. #2278
    Captain abcd567's Avatar
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    Quote Originally Posted by Stephen P View Post
    Been a while, just getting back regarding replacement coco over spidertenna. Changeover back to spidertenna and within half an hour, range out to double.
    Been working away and not had time to changeover or report but has lead to a good benchmark for me.
    Spidertenna = double distance plus
    thanks
    TYBSU3
    The Dark Art of DIY CoCo

  9. #2279
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    Just confirms CoCo is not trivial to tune, at least for UHF and above.
    Small variation on cable VF and construction technique can result in unpredictable results which are imposible to correct without a VNA.

    I am still experimenting with my CoCo to see if I can make it robust to construction variability but this is not easy.

    I am also going to test some variation of collinear which does not require coaxial cable and could be easy to build.

    New Picture.png

    Need to test. 2 stacked half wave like on the picture should be OK but feed impedance might be very low when stacking more half wave phase/radiating sections above.
    If there are antenna specialists on the forum, would like to hear what they think.
    The top sections could be assembled on a fiber glass rod (8mm rods used for kites) which would allow to make the assembly precise and easy.
    The phasing line is just very small diameter copper wire.

    Will try to get something done for next weekend.
    JL

  10. #2280
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    Quote Originally Posted by JLD View Post
    Just confirms CoCo is not trivial to tune, at least for UHF and above.
    Small variation on cable VF and construction technique can result in unpredictable results which are imposible to correct without a VNA.
    Since very few DIY enthusiast have VNA and/or sufficient in-depth knowledge of antenna design, making a Coco by an enthusiast becomes a "Dark Art". Majority of them get poor results far below what is expected or claimed. Only a few lucky ones hit the gold mine by fluke and make a good coco.

    Coco is very alluring to a vast majority due to its simplicity, and because it needs only a piece of coax. The problem shows up only after it is built and put in service.

    I am still experimenting with my CoCo to see if I can make it robust to construction variability but this is not easy.

    I am also going to test some variation of collinear which does not require coaxial cable and could be easy to build.

    New Picture.png

    Need to test. 2 stacked half wave like on the picture should be OK but feed impedance might be very low when stacking more half wave phase/radiating sections above.
    If there are antenna specialists on the forum, would like to hear what they think.
    The top sections could be assembled on a fiber glass rod (8mm rods used for kites) which would allow to make the assembly precise and easy.
    The phasing line is just very small diameter copper wire.

    Will try to get something done for next weekend.
    JL
    Very innovative to experiment with non conventional designs. Waiting for your results.
    Last edited by abcd567; 2015-03-25 at 20:55.

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