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I have a SoM (Snapdragon 820) on a development board . I want to test a loop gps antenna(Antenova-Bentoni-SRFG017-MHF4). I need to add a blocking capacitor to be able to make it work.Where /how can i add the capacitor?

A little more information :

I am working with a development board(Dragonboard 820) which is designed to work with active gps antennas. I want to test a passive (also a loop) GPS Antenna. According to support departmant of board manufacturer , it is possible , but only with a dc blocking capacitor.

Since I do not design the circuit board , i am not able to add anything to it. Should i make a bridge-like connection pcb which have connectors and capacitor on it ? Or what is right/best/known way to achieve that ?

Thanks in advance!

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  • \$\begingroup\$ contact your sales rep (604) 801-6461 : sales@intrinsyc.com but coordinate with your buyer \$\endgroup\$
    – Tony Stewart EE75
    Nov 16, 2016 at 14:28
  • \$\begingroup\$ Have you tried measuring the dc resistance of the antenna? \$\endgroup\$
    – Andy aka
    Nov 16, 2016 at 15:10
  • \$\begingroup\$ @Andyaka No , i did not.I need the capacitor anyhow, don't I? I tried to hang the antenna and boot the board.It did not boot.I contacted with support and they gave me the information I have added to the question. \$\endgroup\$
    – Kaplan
    Nov 16, 2016 at 15:19

2 Answers 2

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Is the antenna on a connector? If so then you can get off the shelf DC blocks e.g. http://194.75.38.69/products/dc_blocks.shtml which will do the job without having to mess with strapping capacitors onto the board. The minicircuits web site is fairly poor but they are a good starting point for any basic RF building blocks, obviously other brands/vendors exist.

You could easily create your own connection PCB with a capacitor on (from memory for GPS frequencies a 15pf 0603 works well) however the time and hassle of getting the impedance matching and shielding as good as the off the shelf products is normally not worth any potential cost savings.

You can also get Bias-Ts which block DC on the RF path but also provide a DC port that allows you to supply power to one side of the connection. They cost a little more but are a more useful thing to have in your stock of RF bits and pieces.

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  • \$\begingroup\$ Thanks for the quick reply. Yes it is with a connector.But it is not a SMA but MHF4 connector , (probably )the smallest connector for antenna.This blocker i have seen during the search in internet.But they are too big.Besides we developed a smartphone-like device.Even i could use it to test the antenna (there is a SMA connection point on Develpoment board -not on SoM ), it would not be realistic due to size limitations. \$\endgroup\$
    – Kaplan
    Nov 16, 2016 at 15:03
  • \$\begingroup\$ About PCB : I can make one.But i searched for mhf4 connectors.Only male ones I could find.I also need a cable with mhf4(female) on both sides which I do not know how to find or do since no female connectors i could find internet. \$\endgroup\$
    – Kaplan
    Nov 16, 2016 at 15:10
  • \$\begingroup\$ I have found some cable with both sides mhf4 female connectors. So the question, if adding a bridge like pcb with capacitor on it for the antenna can be a solution or it affects the signal quality ?Is there a more proper solution ? \$\endgroup\$
    – Kaplan
    Nov 16, 2016 at 16:58
  • \$\begingroup\$ Adding the cables and connectors will give you a hit of a couple of dB, more for longer cables. The pcb will give you a hit of a one or two dB if done right but could cost you 10 dB or more if you mess up the impedance matching. Is this enough to matter? Assuming you're only aiming for reasonable position accuracy then with an active antenna and reasonable GPS you can easily live with a 15 dB hit. With a passive antenna like you want to use I'd be fighting for every dB you can get. But I've no experience with the parts you are using, you may have some margin to play with. \$\endgroup\$
    – Andrew
    Nov 16, 2016 at 17:06
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If not SMA , consider tracing the board and remove the SMD L that provides the bias rather than risk reducing the Return loss by adding a cap that does not have correct geometry for series characteristic impedance relative to ground plane. It must mimic the trace dimensions being cut to not affect s22 which might be a 402 or smaller.

Otherwise, Mini Circuits SMA BLK-89K ac coupler looks good.

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  • \$\begingroup\$ Thanks for the reply.The SoM , I work with, is so small and compact that I am afraid i can not remove anything without damage something else. you can see it here link \$\endgroup\$
    – Kaplan
    Nov 16, 2016 at 15:54
  • \$\begingroup\$ is it an SMA connector? \$\endgroup\$
    – Tony Stewart EE75
    Nov 16, 2016 at 15:55
  • \$\begingroup\$ No it is a MHF4 connector. \$\endgroup\$
    – Kaplan
    Nov 16, 2016 at 15:57
  • \$\begingroup\$ oh well then you add adapters and risk insertion losses data-alliance.net/… \$\endgroup\$
    – Tony Stewart EE75
    Nov 16, 2016 at 16:34

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