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  • iamnothere
    replied
    Thanks , abcd567

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  • abcd567
    replied
    Originally posted by AzKo View Post
    Build spider today when finally get some stuff to build something. And im not also so good solder. But main thing is that antenna is working

    [ATTACH=CONFIG]6265[/ATTACH]
    Good work!

    Spider is one of the easiest and very reliable antenna for begginners. In fact all antennas with a wavelength (69mm) whip and a groundplane (metal disc, horizontal radials, slanting radials, or a food/drink can, also known as Cantenna) are ideal for beginners.

    The reasons are:

    (1) These antennas are naturally resonant, i.e. have an impedance close to 75 ohms, which matches with the Coaxial cable, Amplifier & Receiver (dvb-t) impedance and gives a swr less than 1.5, a highly desireable situation.

    (2) These antennas have high dimensional tolerance, so few mm error in length of whip or radials or few degrees error in bending down the radials does not appreciably degrade its performance.

    Dont worry about soldering. The antenna works good even if the soldering is not very good.

    Please click the link below to see 4 different antennas, all with wavelength whip, but each with different methods of providing groundplane.


    http://forum.flightradar24.com/threa...-FOR-BEGINNERS
    Last edited by abcd567; 2015-07-20, 23:38.

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  • AzKo
    replied
    Build spider today when finally get some stuff to build something. And im not also so good solder. But main thing is that antenna is working

    2015-07-20 22.39.17.jpg

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  • abcd567
    replied
    Originally posted by iamnothere View Post
    This is my 2nd quarter wave antenna with 8 legs, new build have not install yet , first one is on duty .
    [ATTACH=CONFIG]6262[/ATTACH]

    Another antenna I made month ago , it prove my solder skill pretty bad .
    [ATTACH=CONFIG]6263[/ATTACH]
    Well done! Keep experimenting. That is how you are going to learn & find the best antenna built for your system. Dont worry about soldering. Many of us (including me) have worst soldering skill than your's.

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  • abcd567
    replied
    Trial Runs for Comparison of FRANKLIN SPIDER (With Impedance Matching added), Spider, and Franklin Spider.


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  • iamnothere
    replied
    This is my 2nd quarter wave antenna with 8 legs, new build have not install yet , first one is on duty .
    IMG_5535.jpg

    Another antenna I made month ago , it prove my solder skill pretty bad .
    IMG_5463.jpg

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  • abcd567
    replied
    Originally posted by AzKo View Post
    I made also this Franklin Spider antenna today. Lets see how it performs. And thanks abcd567 at good antenna tips
    The Franklin Spider is inferior to Spider if impedance matching is not used, but can be made superior to it by impedance matching, as shown in above post.

    Today I have tried two tweaks in values of the two parameters of impedance matching as below:

    (1) Soldered a third 1 pF Capacitor in parallel with existing two, increasing the total value of Capacitor from 2 pF to 3 pF

    (2) Tried two different lengths of transmission line between the Antenna & the Capacitor. Original was 210 mm (including length of connectors at both ends). I made two more, one 225 mm (including length of connectors at both ends), other 240 mm (including length of connectors at both ends).

    The combination of 3 pF Capacitor & 240 mm Transmission Line (including length of connectors at both ends) between Capacitor & Antenna resulted in Franklin Spider surpassing the performance of Spider.

    Since each built of DIY antenna is slightly different, these values (240 mm / 3 pF) may not be optimum for every one, but sure will be close to optimum, provided RG6 Coax cable (with VF 0.83 to 0.85) is used as transmission line piece between Antenna & Capacitor, shown in photo in my post #2395.
    Last edited by abcd567; 2015-07-20, 01:29.

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  • AzKo
    replied
    I made also this Franklin Spider antenna today. Lets see how it performs. And thanks abcd567 at good antenna tips

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  • abcd567
    replied
    Due to yesterday's abnormal graph, I checked my system and found a defective (dodgy/intermittent) connector. I replaced the connector and repeated yesterday's test, and results are now normal as follows.

    1) When The λ whip was replaced by Franklin whip, there was a distinct drop in performance to about 40%.

    2) When crude impedance matching was added to the Franklin Spider, there was a distinct increase in performance, jumping up from 40% to 85% of Spider.

    Now I have to optimize the matching network by:

    1) Using an adjustable trimmer capacitor 2 - 5 pF instead of fixed ceramic capacitor of 2 pF.

    AND

    2) Try three lengths of transmission lines (i.e 205 mm, 210 mm & 215 mm) between antenna & capacitor.

    I hope I will be able to achieve optimum matching, in which case the Franklin Spider's performance will (hopefully) exceed Spider's performance.




    .
    Last edited by abcd567; 2015-07-19, 02:44.

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  • abcd567
    replied
    In the above trial run of matching network for Franklin Spider, I had to make some assumptions & aproximations. As a result, the matching is aproximate, not optimum. I am now planning to optimize matching network by trial & error.

    (a) I will replace fixed ceramic capacitor by adjustable (2pF to 5 pF) trimmer capacitor.

    (b) I will make & try two more pieces of transmission line, one 5mm less (i.e.205 mm total length including connectors at both ends) other 5mm more (i.e. 215mm total length including connectors at both ends).

    I hope I will be able to get still better results than the crude matching I have done now.
    Last edited by abcd567; 2015-07-18, 13:26.

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  • abcd567
    replied
    I have noted something wrong in the graph of collected data I posted above with impedance matching. When I changed wavelength whip with Franklin whip (i.e. converted Spider to Franklin Spider), all the graphs became nearly zero. I have previously swaped the Spider & Franklin whips several times, and each time the graphs dropped to about 40%, but not almost zero.

    To clear the matter, tomorrow I will repeat the experiment about the same time and post graphs.

    Inspite of above abnormal behaviour, the jump back of Franklin Spider graph to level of Spider after addition of impedance matching, clearly prove the effectiveness & success of impedance matching method I have used.

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  • abcd567
    replied
    Franklin Spider Failure Reason - Impedance Mismatch


    The Spider has an impedance close to ideal 75+j0 ohms. The SWR is about 1.3

    The Franklin Spider has an impedance 176+j0.14, far from ideal 75+j0 ohms. The SWR is about 2.35

    As a result Franklin Spider gave inferior performance than Spider.

    I now attempted a CRUDE impedance match (many approximations in calculations and factors & use of capacitor 10% lower than required) and still got a dramatic improvement. Please see data graphs below:


    .


    And this is how I achieved it:

    Step 1 of 3: Starting point is antenna impedance by simulation


    Step 2 of 3: Calculation of length of transmission line piece & value of series capacitor by Smith Chart.
    Length of Transmission Line between Antenna & Capacitor (including length of Connectors) = 210 mm RG6, VF = 0.84 (assumed)
    Capacitor = 2.2 pF.
    I did not have a 2.2 pF capacitor, but had many 1 pF capacitors, so I put 2 capacitors of 1 pF in parallel, which gave me 2 pF, 10% less than required 2.2 pF. I will now purchase a 2 - 5 pF trimmer (adjustable capacitor) and replaced ceramic ones by trimmer and try to fine tune the response to optimum.


    Step 3 of 3: Built & put on trial run


    Later Addition: Later tweaking showed that using a 3 pF Capacitor (instead of 2 pF Capacitor) and 240 mm Transmission Line (instead of 210 mm transmission line) improved performance, and Franklin Spider surpassed Spider.

    Last edited by abcd567; 2015-07-20, 05:20.

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  • cloud_9
    replied
    Originally posted by HermanZA View Post
    119mHz I can assume is voice comms, but what happens on 1575mHz ?
    GPS L1 1575.42 MHz.

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  • HermanZA
    replied
    119mHz I can assume is voice comms, but what happens on 1575mHz ?

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  • cloud_9
    replied
    This is my AirNav antenna.Is it a spider or is it a simple collinear with ground plane and does anyone one know the retailer for this one.Apparently it's a 3 in 1 antenna(119.1 + 1090 + 1575 Mhz).

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