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  • Stealth
    replied
    @abcd567

    Maybe I didn't convey in that post that I'm on top of the basics.

    The point of the post was to relate how dramatic the effect of signal overload can be. It wasn't just a reduction in displayed aircraft or range, it was a drop from seeing numerous aircraft, some beyond 175nm to seeing virtually nothing. Virtually nothing was just one aircraft within about 15nm. It was way more dramatic an effect than I would have imagined.

    Some additional learning points from this scenario were:

    + Don't assume an antenna is going to work well solely based on reflected power reading i.e. VSWR, however its a good sign that it will work to some degree
    + Range should not be used as the sole indication of antenna effectiveness, look at message rate and the number of 'hits' over a significant period of time
    + Finally, don't ever take something at face value, check it out

    My 'fall back' and the 3 element co-linear I mentioned previously are shown below (original graphics as downloaded, not my actual versions).

    150_x_150 colinear.jpg

    5-8th.jpg

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  • abcd567
    replied
    @Stealth

    I suspect your "fall-back antenna" is a low gain simple antenna like the mag-mount Whip (supplied with dvb-t), or Spider or Cantenna. These simple antennas pick comparatively less cell/mobile signals, and the 1090 mhz signal is not "drowned" into the strong cell/mobile signals.



    Below is the RF Scan of signals at my location showing strong Cell Phone signals.

    The scan was done using OPTION-2 (DVB-T plugged into Windows computer) of following thread:

    Find Out Existing RF Signals (Cell/Mobile/Pager etc) In Your Area

    Last edited by abcd567; 2018-05-19, 17:41. Reason: Fixed broken image of scan

    Leave a comment:


  • Stealth
    replied
    Playing with antennas is the best part of this pursuit. Last week I was about to build my third co-co in recent times, first two were duds. No matter what I did with them the analyzer kept showing a low VSWR everywhere but 1090. So for a change I built a three element co-linear using coax screen and built on a 6mm fiberglass rod, three simple coils and all was ready to go. Analyzer showed around 1.6 VSWR. Down with the mast, up with the antenna. Rush indoors to see results.......nothing, blank screen.

    Back to the fall-back antenna and a re-think. Decided to get a FA antenna express mailed, just to give me a commercial benchmark. Arrived today, wait for the wind to die down and up it goes. Expecting glorious signals, hurry inside. One measly signal within 20 nm, nothing else.

    Much head scratching, try a few changes on the gain settings and two or three signals close in. I wonder, so drag out the bandpass filter and insert. Bingo! Signals flooding in and at a very decent rate. The FA antenna had brought enough signal in to completely overload the FA Pro-stick Plus.

    Now I wonder if my co-linear from last week was good after all and I had the same issue........

    I should mention that the 'fall-back' antenna had been receiving quite well, worst was out to 100nm best out to 200nm + in some directions.
    Last edited by Stealth; 2018-03-20, 12:50.

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  • abcd567
    replied
    CONGRATULATIONS!

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  • petercr
    replied
    Looks like the new antenna is working based on the last 7 days...
    new antenna.png
    (and today is only just 4hrs old based on GMT)

    max range last night was 145Nm

    Leave a comment:


  • abcd567
    replied
    Great to know you already have experiance in DIY antennas by helping your dad, an amateur radio enthusiast.

    Yes, DIY is cheaper for sure . This is in addition to the fun and satisfaction it gives.

    Leave a comment:


  • petercr
    replied
    Originally posted by abcd567 View Post
    Hi Peter
    Good that you have decided to make a DIY dc blocker.
    DIY is fun.
    My Dad was an amateur radio enthusiast from the time he got out of the RAF at the end of WWII until he died (about 20yrs ago) and I fondly remember helping build a number of his antennas so this does bring back some memories...

    (and DIY is often cheaper )

    Leave a comment:


  • abcd567
    replied
    Hi Peter
    Good that you have decided to make a DIY dc blocker.
    DIY is fun.

    A 100pF capacitor is ok. The 200pF is not critical, but preferable.

    The impedance added in RF path by 200pF capacitor is 0.73 ohms. As the 100pF has half the capacitance, its impedance is double i.e. 2x0.73 = 1.46 ohms. Both these values are low enough to be acceptable.

    As the prices of 100pF and 200pF are nearly same, I preferred to use 200pF to get slightly lower impedance at no extra cost.

    XC = 1/(2 x pi x f x C) = 1 / (2 x 3.141 x 1090 x 106 x 200 x 10-12)
    = 0.730 ohms

    Leave a comment:


  • petercr
    replied
    Hi abcd, (having read this far I feel I sort of know you)

    Voltages on both F-connectors are correct (about 17V on the amp side as it's no-load without the amp connected) and 0V on the TV side. I have a spare 2-way splitter that I've gutted and there's a hobbyist electronics store 10mins down the road where I can get 220pf ceramic caps for less than a dollar so I might make a power blocker as well as an extra precaution...

    (or I can put 2x100pf in parallel if 200pf important - caps come in a pack of 2pc so no problem either way)
    Last edited by petercr; 2018-03-19, 04:27.

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  • abcd567
    replied
    @petercr
    1. There are two output ports in power inserter, one for TV, other for Amplifier.
      In the powered-up condition, when measured with a multimeter:
      • The terminal for TV MUST have zero DC voltage to protect TV (or the DVB-T dongle)
      • The terminal for Amplifier MUST have full DC voltage (say 14V DC or similar).
        Zero DC at this terminal means no power supply to amplifier and the Amplifier wont amplify. It will rather attenuate.


      Power Injector - DC Voltages.png

    2. Test continuity of your antenna between core and shield at feed point by a multi tester. If it shows open circuit, then DC Blocker is not necessary. However even with open-circuit antenna, it is safer and desirable to have DC Blocker so as to protect your power insereter and amplifier from damage in case of accidental short circuit.

    Leave a comment:


  • petercr
    replied
    I did notice that comment while reading through all those pages so I got out my multimeter and measured the DC voltage across the output connection of the power inserter when powered up and it was zero so I know it's safe... (it's also from a well-known Australian antenna manufacturer so I doubt they'd forget about that).

    Edit:
    Same as this except with F-type connectors...
    https://www.kingray.net.au/catalogue...ors/psk06.aspx

    Extra edit: When assembling, I did a continuity check of each segment and all okay. The open end was also encapsulated in non-conductive epoxy to bond it to the end cap on the PVC pipe.
    Last edited by petercr; 2018-03-18, 20:32.

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  • abcd567
    replied
    @petercr:

    The built-in DC blocker of power supply blocks DC only from going to the DVB-T (or Pro Stick). It definitely allows DC to go to the Satellite amplifier, which passes the DC to antenna. If the antenna has a DC short, your DC power supply will fry itself or fry the amplifier.

    The DC blocker MUST be between Satellite Amplifier and antenna. This requires a separate dc blocker.




    https://www.ebay.com/itm/DC-Blocker-...g/132336080669

    DC Blocker F inline.jpg

    https://www.ebay.com/itm/DC-BLOCKER-...-/131036281185
    Last edited by abcd567; 2018-03-18, 14:52.

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  • petercr
    replied
    Here's the antenna with an addition I made this afternoon - the bottom section is a piece of 50mm PVC-U pipe with caps and IP68-rated cable glands that should be totally water-proof. When the satellite amp arrives I intend to fit it in there along with the power supply.
    IMG_20180318_160425_1.jpg

    Leave a comment:


  • petercr
    replied
    De-lurking after reading all 271 pages... Today saw me install an 8-element open top CoCo using RG6 inside a 3m length of 15mm (1/2" for you non-metric types) PVC conduit attached to a j-bracket and with the limited horizon I've got (due to the house and other tall gum trees and palm trees in the area) I've managed to get a max range of just over 130NM after about 12hrs of reporting. Have ordered a Prostick+ and separately from eBay one of those generic 20dB satellite amps (along with a TV amp power supply (with built-in DC blocker) that was lying around) - see which one turns up first... Hopefully I can get my range up even further.

    Leave a comment:


  • lodervsm
    replied
    Thanks for your tips.

    I have reduced my gain in the last couple of days and seems that --gain 42.1 is a good compromise to my system. I also added an extra filter after the antenna. Now my max range has reached 311NM. I noticed that for my position somehow it helps to have a southerly wind for max range.

    Leave a comment:

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