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GPS antenna alternatives

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  • Yes bias tee is the correct name, but they tend to cost more than the 'satellite tv dc injectors' which perform the same function. The cheap ones made in China sell for just a few $ and work perfectly OK in this application. If you buy a bias tee from Mini-Circuits it will typically cost $50 USD or more as they are selling into a different market.

    Regards,

    Martin - G8JNJ
  • edited August 2018
    Hmm, it would seem that times have changed since we used to buy bucket loads of DC injectors at about $2.50 USD each. They now seem to be retailing for about $20 USD, which is quite a markup.

    Looks like currently the cheapest option is a bias tee from a Chinese supplier, unless you build one yourself.

    3 to 5 turns air spaced self supporting made from thin enamelled wire, initially wound on the shank of a 3mm drill, as the inductor.

    47pF (or something around that value) as the DC blocking capacitor.

    Keep all lead lengths as short as possible.

    Regards,

    Martin - G8JNJ
  • This was what I was thinking might be the case, hope I did not damage the GPS IC running with this. I'll put the old puck back on and make sure it still works, and wait for this $10 bias-T to come in.
  • I'm using a PCTEL 40 dB antenna and the voltage being fed to it by the Kiwi measures at 3.139 V. It seems to be working more or less OK although it does seem to go a bit deaf at times, so maybe I need to beef it up a bit.
  • "Short circuit current can be sustained indefinitely" says the data sheet. So you should be okay. But I_lim_abias is 50 mA so if you try and draw anything above that the 3.3 will start dropping.
  • On second thoughts, I don't think my antenna is going deaf at times. The Kiwi seems to struggle to acquire sats when the server has been running for a few hours. Last night it had 11-12, but by this morning it was down to six. On restarting the server it immediately came back to 11-12. If this is a bug, I suspect it's been there a while.
    Powernumpty
  • G4DYA: Yes I have also observed the same GPS behaviour with Kiwi struggling to acquire sats after running a few hours. I noted this when the TDoA extension was introduced.

    Best regards

    Mauritz / SM2BYC
    Powernumpty
  • I have observed same 10-11 then later 5-6
  • There doesn't seem to be anything wrong with the PCTEL GPS-TMG-40N antenna's current draw. The data sheet says <=40 mA, and I've just measured mine at 23 mA, both well within the Kiwi's 50 mA current limit.
    Powernumpty
  • I put the old puck back on, GPS is working fine.
  • Stuck my PCTEL up today, just on a pole to test. Question; what is the downside of having "Always acquire" on and is there a solid advantage?
    I turned it on when I first got the antenna, got to 12 Sats, turned it back off and left it for a while and the GPS was back to 6/6 Sats, back on up to 11 within seconds.
    Is the always acquire option aimed at moving targets and with it off does dropping back to six satellites give enough accuracy that any more is just extra processing?

    Attachments:
    http://forum.kiwisdr.com/uploads/Uploader/24/c0d9b5ea364669b8159e8a07f61c73.png
  • PCTEL at 68hrs and 15minutes (after reboot). I have got it set to reboot each day but the WSPR channels are putting that off.
  • At KPH I use a PCTEL at the end of 100' of RG-6 through a 8 way passive MoCA splitter (https://smile.amazon.com/gp/product/B01M34OZ2S/ref=oh_aui_search_detailpage?ie=UTF8&psc=1). All 5 Kiwis are locked to 10-13 satellites and the resulting frequency accuracy and stability is very good. It is strange to see the shadow to the north, since the sky view is clear in all directions.

  • I have posted info in the past about the northern shadow, that is normal
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