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I am trying to build an antenna to connect to the GOES-16 satellite (downlink at 1690,1MHz, linear polarization) with my SDR. My plans are using a 1m offset parabolic dish with a BiQuad feed, connected to a RG-58 coax line (50 Ohms) and followed by a filter (I have not decided yet wether to use a SAW filter or a end-coupled microstrip one)and a 20dB LNA. I live in a place where it will be difficult to get the signal from the satellite due to its low elevation and interfereces, so it is crucial for me to optimise the most the design.

Since the BiQuad is a type of dipole, I imagined that I would need a balun to improve the overall performance of the antenna. Assuming that the antenna is sufficiently well matched to the 50Ohm coaxline, only a 1:1 balun would be needed. However, most of the SMD baluns I find that handle this frequency carry an insertion loss of around 1-3dB with them. Hence, my questions:

Is it still worth adding the balun in spite of the big insertion loss? Would the losses/noise of the receptor without the balun be more inportant that those 1-2dB? Do homemade baluns (5-6 turns of coax cable) also have this insertion loss?

Thank you in advantage.

Edit: changed values of insertion loss to more common ones

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  • \$\begingroup\$ 2-3dB is pretty poor. Here's one that's 0.3dB everythingrf.com/products/microwave-rf-baluns/… \$\endgroup\$
    – Bruce Abbott
    Jul 13, 2019 at 15:48
  • \$\begingroup\$ @Bruce Thank you for the info. However, at aroun 1,7GHz, the insertion loss is still aroumd 1dB. Is it worth it in this case? \$\endgroup\$
    – user3141592
    Jul 13, 2019 at 15:51
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    \$\begingroup\$ I'm no expert on satellite receivers (I imagine severe interference issues with an unbalanced dish, but I have no experience in this area). Just pointing out that lower loss baluns are available. 1dB probably isn't enough to worry about, but there may be baluns optimized for 1.7GHz which are better. \$\endgroup\$
    – Bruce Abbott
    Jul 13, 2019 at 16:08
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    \$\begingroup\$ RG-58 is rather poor co-ax. You need to use low-loss. \$\endgroup\$
    – Leon Heller
    Jul 13, 2019 at 16:18
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    \$\begingroup\$ baluns are worth a lot in performance if the cable is imperfect in ingress and results in Poor C/I ratio . The SMD or cost does not need to be high but design depends on current, conduction loss, bandwidth . For short lengths , I would use semi-rigid coax or an LNB or RG9 or 212 or some low loss coax compatible to your connectors. \$\endgroup\$
    – Tony Stewart EE75
    Jul 14, 2019 at 12:52

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The answer depends on your HW configuration. Maybe you can add additional information on your HW.

A dipole is a balanced antenna, meaning that signal wave-forms are complimentary to each other on both elements of the antenna. If your receiver has a balanced RF input, then you don't need a balun. You might need a matching network though. On the other case if you have an un-balanced RF input, you will need a balun (=Balanced to Unbalanced).

Cheers.

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