Coaxial cable problem
I am trying to construct a balun for my quadrifilar antenna using suitable coaxial cable. I tried to use RG174 for the balun but suffered a huge attenuation at the outcome. Thus, would like to consult some experts on which type of coaxial cable that I should be using to minimize the attenuation. Below are the specifications for my antenna.
Type: Quadrifilar Helical Antenna
Operating frequency : 1.575GHz
Input impedence : 50Ω
Type of balun to construct: http://www.qsl.net/iz7ath/web/02_bre.../pag13_eng.htm
Would appreciate if anyone will be able to help me. Thank you.
Yong
Try RG-58C/U (MIL-C-17G) ..
It should work well in this frequency range ..
Regards,
IanP
Hi keigo82
look at https://www.edaboard.com/viewtopic.php?t=73468
I think it will help you
pl
RG174... hmmm, is very close to filament wire to make heaters...
But short length of RG174 in balune itself have not so much impact on loss compare if you using RG174 as feeder cable to antenna
RG223 is better (double screened) than RG58 and RG214 for approx half of loss of RG223/RG58 and still not so hard to handle physical and mounting connection (crimping) compare to semiridge cable from 1/4" and up.
But possible biggest problem here is feeder cable loss and know if antenna is matched or not (200 Ohm for 4:1 balune and 50 Ohm system), very short length of cable in balune make not so much loss even if using high losses RG174 (~1dB/m loss). Half wave for balune sling as 1575 MHz and RG174 (c=0.6) is around 56.4 mm and make no more than 0.05 - 0.1 dB loss.
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Have Plasma possibly to measure return loss or standing wave on couple of frequencys around 1575 MHz? (measured directly on balune) - antenna(system) should be have 200 Ohm impedance for perfect match to 4:1 balun in 50 Ohm system (> 20 dB return loss), 300 Ohm antenna give as best as 13.5 dB return loss and 150 Ohm antenna give around 16.5 dB returnloss on 4:1 balun (50 Ohm) for example.