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  1. #1
    Join Date
    26th November 2009
    Posts
    5,214

    900Mhz Yagis on ebay

    This is a nice quality 916Mhz Yagi antenna that can be used for ground recovery of
    the 900Mhz trackers out there: https://www.ebay.com/itm/NIB-Linx-5-...EAAOSwbqpTvrAV

    Price is cheap and I picked one up. Get an N male to SMA adapter cable to fit ones receiver
    and would be in business for ground recovery.

    Note well. This antenna solution is generally best used after ones rocket is down and it or
    other 900Mhz Yagis can increase the ground footprint of the tracker. If your rocket lands nearby, you don't need it but if it lands quite a distance away and you have to walk to it, you can put this on your receiver and point it in the direction you know the rocket is at. Generally hold the elements horizontally or if you think the rocket is in a tree and the antenna is up and down, hold the elements so they are vertical. Doing a search on Ebay will lead to higher gain Yagis available but beware, you need to be comfortable carrying the thing. The goal is to achieve a larger ground footprint to improve one's chance of recovery when pushing a 100mW tracker to the limits.
    Trying to point a Yagi antenna at a sight unseen rocket might result in lost positions and if receive gain is desired for flight tracking, try a patch antenna like this:
    Click image for larger version. 

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    The beamwidth on a patch antenna is wider than a Yagi on this frequency so one can achieve some additional in-flight range and still have some directivity.

    I noticed increased reception of positions with 100mW trackers with the patch antenna (which at the time I got it was $19.99. Lucky to find anything like that anymore.) and the Yagi does
    indeed improve the ground footprint for recovery.

    I've done two ground recoveries with EggFinders where once loss of signal (LOS) occurs, I
    plug the Yagi antenna in and proceed towards the last known position. When the EggFinder LCD starts beeping a new position as I approach the rocket (which both times I still couldn't see lying on the ground) I replaced the Yagi cable with the vertical dipole "duck" antenna.
    Both times the signals disappeared. This proves the Yagi increases the ground footprint
    as would be expected.

    Again, this might be helpful when pushing a 100mW tracker to the limits. What are the limits? It would depend where one is flying. A lot of hillocks and depressions and the ground
    foot print can be drastically cut with the tracker. If the LOS occurs at a 2 miles out from 100 feet in the air and there are hills are depressions a Yagi might be the edge at getting a 900Mhz tracked rocket recovered especially if the final lie of the rocket is quite some distance away from the last known position.

    Kurt


  2. #2
    Join Date
    27th May 2015
    Location
    Charleston, SC
    Posts
    184
    Kurt-thanks for the link, even a home brew 900 MHz yogi would definitely be more costly. As you point out, the use of a yogi antenna would significantly expand the receiving distance of a 100 mw transmitted signal.

    Fred, L2
    KG4YGP
    member of ICBM, S.C.


  3. #3
    Join Date
    26th November 2009
    Posts
    5,214
    Quote Originally Posted by FMarvinS View Post
    Kurt-thanks for the link, even a home brew 900 MHz yogi would definitely be more costly. As you point out, the use of a yogi antenna would significantly expand the receiving distance of a 100 mw transmitted signal.

    Fred, L2
    KG4YGP
    member of ICBM, S.C.
    But I'd reserve it for terrestrial use to improve the ground footprint. I believe the sale is over but I received mine.
    Pretty nice. Sport flying is overkill but if pushing a 100mW tracker far, might come in handy for ground recovery.
    Kurt

  4. #4
    Join Date
    23rd October 2015
    Location
    Canberra, Australia
    Posts
    89
    Quote Originally Posted by FMarvinS View Post
    ... a yogi antenna ...
    Good for detecting bears, I suppose!

    However, these are very good. Not as cheap, but not expensive.

    http://store.rfdesign.com.au/antenna-900mhz-6dbi-yagi/

    Cheers and a happy New Year guys
    John
    TRA #14574 L2

  5. #5
    Join Date
    11th February 2017
    Location
    south Florida
    Posts
    634
    9-element 900mhz yagi on eBay now for $14 shipped:
    https://www.ebay.com/itm/YA90011-DMS...-/112516184562

    And see page 3 of this document for a 900mhz version of WA5VJB's famous Cheap Yagi:
    http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf
    I made one of these for 70cm and have been using it successfully with my Telemetrum. Also used the 2m/70cm version to work the ham satellites. You can make these in less than an hour with a piece of wood and some #10 wire.

    L1 3/25/17 H135 Wildman Darkstar Jr
    L2 8/12/17 J180 LOC Expediter
    L3 3/17/18 M1350 Painkiller Max

  6. #6
    Join Date
    30th May 2017
    Location
    vermont
    Posts
    76
    I built this for my 70CM tracking device, it looks cheap but still works very good.
    http://zaarc.org/70cm_yagi.pdf
    Eric M
    NAR#85115 L2

  7. #7
    Join Date
    26th November 2009
    Posts
    5,214
    As long as you run it at 433.920 Mhz you'll be optimized to the n'th degree for whatever 70cm
    tracker you're running. Have fun! Kurt KC9LDH

  8. #8
    Join Date
    26th November 2009
    Posts
    5,214
    Here's a couple of Yagi's that were had for $15.00 on ebay. Not bad for ground recovery use.

    Click image for larger version. 

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    The longer one is the one billdz mentions above and the other one above it was
    a 9db gain one I found that has a center frequency of 916Mhz which is great for the
    EggFinders. The longer 11dB Yagi I calculate is around 925Mhz for the center frequency.

    I was able to slide a bicycle handlebar grip on the 11dB antenna but the base of the 9dB is
    smaller and can't use the grips I have.

    Again, these are best used on the ground recovery phase to increase the ground footprint of the tracker. If the rocket is lying on the ground, the tracker antenna is likely horizontal so hold one's Yagi with the element horizontal. If you think the rocket is (heaven forbid) hanging in the trees or off on some wires, hold the Yagi so the elements are vertical.

    If you don't know, twist back and forth between vertical and horizontal while coming in closer to the presumed rocket position.

    If you don't believe me that the Yagi improves the ground footprint, once the rocket is down,
    take off the little vertical dipole and plug in the yagi. Walk towards your downed rocket, I'm presuming you've lost the signal once the rocket is down and are using an EggFinder LCD that beeps. Once it starts beeping with the Yagi, disconnect it and put on your screwon vertical dipole. I expect you'll lose the signal. Screw the Yagi back in and you'll get it back.

    Again, I wouldn't use the yagi for in flight tracking but use it to increase the ground footprint once the rocket is down.

    For the 70cm, 1.25 meter and 2 meter bands the beamwidth of the Yagi antennas is broad enough that if one points them in the general direction of the rocket they'll likely receive a signal. Hence one sees them used on these bands readily. On 900Mhz/33cm band the beamwidth especially of the high gain Yagis are so narrow that they could be hard to aim
    at a moving rocket in flight. Once it's down it's easier to point the antenna and aim it at a nearly stationary object to receive an updated GPS position. Kurt


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