You can get much more than 5% improvement, if you make some trial error adjustments as follows:
There are two parameters to be found by trial & error, detailed below.
(1) Value of Capacitor
Try using lower value of capacitor, say 1.5 pF. If you dont have 1.5 pF, put 2 capacitors of 2.7 pf in series, and it will give you 2.7/2 = 1.35 pF
(2) Distance from antenna at which Capacitor should be inserted.
Try reducing & increaing the distance of splitter from antenna, 1 cm at a time.
Point of insertion along coax should be:
n x L + 0.85 x L,
where L = ½ wavelength in air (138 mm) x VF of coax,
and n can be any whole number 0, 1, 2, 3, ..., 10, .... etc, but n being smaller, the results are better.
So if n is selected to be 0, distance should be 0.85 x L, i.e. slightly less than ½ half wavelength.
The factor 0.85 above is rule of thumb, best value to be found by trial & error.
Oops... wrap the splitter in self bonding/self amalgamating tape, or install inside a weather proof box......but decreased by 40% thanks to rainwater getting into the two-way splitter.
Last edited by abcd567; 2015-09-04 at 00:50.
@YSWG
You have mentioned the coax length between antenna & capacitor is 1 meter.
If your coax has VF=0.66
Length of ½λ piece of coax = VF x 138 mm = 0.66 x 138 mm = 91 mm
Number of ½λ pieces in 1 meter coax = 1000 mm/91mm = 10.989 pieces.
Out of above, take out the 10 complete ½λ pieces (as these do not play any part in impedance matching), and balance fractional part is 0.989 of ½λ, which plays real role in impedance matching. This seems too high, as normally the optimum lies between 0.75 and 0.9 of ½λ. So better cut-off 1 cm piece from this 1 meter to make the effective fractional piece about 0.9 of ½λ, and try. If you see some improvement, cut another 1 cm and try again.
Last edited by abcd567; 2015-09-04 at 05:10.
I'll give it a try, though the mast needs to be taken down to do it. :/
F-YSWG1 and T-YSWG2
I am lucky that I dont have any mast. Me and my antenna both live at same level, at my arms reach, inside my apartment near a large window, ideal for testing/experimenting.
It is ideal to have your antenna at arms reach without need to lower the mast, climb a ladder, climb the roof etc.
Make a new antenna, and put it in your back yard or in a room, near window. You can then do the trial & error effortlessly. Once you have adjusted the Capacitor & Length of Coax piece to optimum, you can take your antenna up the roof or mast.
Last edited by abcd567; 2015-09-04 at 19:08.
Made the change you suggested but it has been a negative. Even adding different capacitors didn't so a how lot. Maybe I shouldn't have touched it, was getting good results.
dump1090-rpi-acs-24h.pngdump1090-rpi-rate-24h.pngdump1090-rpi-signal-24h.pngdump1090-rpi-local_rate-24h.png
F-YSWG1 and T-YSWG2
Remove capacitor and revert back to original direct connection of feeder coax to antenna.
It seems your antenna has already close to 75 ohm impedance. Adding capacitor for impedance matching in this condition will not make any improvement, or may even worsen the performance. The insertion of capacitor is effective for those antennas which have a high impedance / poor SWR.
Example:
Mr. A had poor vision, he started using corrective glasses. Now he sees good.
Mr. B had normal vision. He was fascinated by improvement of Mr. A's vision by wearing glasses, so he tried glasses, and his vision worsened.
EDIT
Did you try diffirent lengths of coax between capacitor & feed point? This length is also important. I tried pieces of coax 0.75, 0.8, 0.85, and 0.9 of ½λ with a capacitor of 2 pF, and found the 0.85 x ½λ (i.e. 0.85x½x275xVF) gave best result for MY Coco (YOUR Coco may require different length than this, but within 0.75x½λ to 0.9x½λ range).
Once I determined optimum length, keeping that length I tried 2.5 pF, 2 pF, 1.5 pF and 1 pF capacitor and found 1.5 pF gives best result for MY Coco. (with YOUR Coco's optimum piece of coax, YOUR Coco may require a different value, but within 3.5 pF to 0.5 pF range).
Last edited by abcd567; 2015-09-12 at 20:32.
There are many antennas available which can solve your problem. Now days the microstrip antennas are too efficient. Can you please explain your purpose? I mean for which application you are looking an antenna. Also the methods are there that you can design your own antenna with the help of simple tools.