Hello Ab cd,IMPROVED RANGE BY CHANGING STUB CONDUCTOR SPACING
For my Franklin antenna, I was using an impedance matching stub in which spacing between stub conductors was 5mm (due to 5mm spacing of terminal screws in the terminal block for adjusting the tap position).
I dig-up some theory about impedance matching by stub, and found that if I increase the spacing of stub wires to 10mm, I will get a much better impedance match.
I increased the spacing to 10mm and put antenna on trial run for 24 hrs. I could gain about 75 to 100 km extra in all directions.
Below are two coverage screen-shots, one for a 5mm spacing stub, and other for 10mm spacing stub.
Image 1 of 3 - Coverage with 5mm spacing of Stub Conductors
View attachment 352
Image 2 of 3 - Coverage with 10mm spacing of Stub Conductors
View attachment 353
THEORY & CALCULATIONS
Image 3 of 3 - Calculations
View attachment 354
For matching impedance of Antenna with impedance of Feed Cable, the quarter-wavelength stub's impedance ZSTB shoul be:
ZSTB = √ (ZFDR x ZANT)
For RG-6 cable: ZFDR = 75 Ohms
For Full-Wavelength Dipole / Franklin Antenna: ZANT = 1600 Ohms
Hence required stub impedance ZSTB = √ (75 x 1600) = 346 Ohms
Calculated Stub impedance from it’s dimensions
ZSTB = 276 log10 (2S/d)
where S = conductor spacing in mm, d = conductor diameter in mm
Stub conductor is #18 AWG which has a dia of 1mm
CASE A - 5mm SPACING BETWEEN STUB CONDUCTORS:
S = 5mm, d=1mm
Hence ZSTB = 276 log10 (2S/d) = 276 log10 (2x5mm/1mm) = 276 log10 (10) = 276 x1 = 276 Ohms
Conclusion: Mismatch - 276 Ohms provided vs, 346 Ohms required
CASE B - 10mm SPACING BETWEEN STUB CONDUCTORS:
S = 10mm, d=1mm
Hence ZSTB = 276 log10 (2S/d) = 276 log10 (2x10mm/1mm) = 276 log10 (20) = 276 x1.301 = 359 Ohms
Conclusion: Matched closely - 359 Ohms provided vs, 346 Ohms required
http://forum.planefinder.net/members/richard-lee.497/The inline amplifiers such as the one here http://www.ebay.co.uk/itm/IN-LINE-S...?pt=UK_Sound_Vision_Other&hash=item3ccdc6c614
does anyone know what sort of power they require (amps) and any recommendations for suitable power supplies (in UK) . I can find one psu rated at 14v but I think that's an off load rating, not sure what it would drop to on load - plenty of 12v psu's around
The diameter of wire affects:Hello Ab cd,
I've 2 questions,i beg your pardon,I'm a newbie:
I would realize a Franklin collinear antenna , could diameter of conductor have effect on reception? I've some lenghts of internal copper conductor of coaxial cable Belden H 1000 type 2,62 mm diameter.....
Do you suggest to use another diameter?
What happens if i use a 50 ohm cable( Belden H 1000) instead of a 75 sat ohm cable?
thank in advance,kind regards and compliments for your work....
There is a 1:9 ratio between air band frequency 120Mhz and ADS-B 1090 Mhz. The VHF antenna power will be fed to receiver, as well as the inLine amplifierks "out" port, which normally has high impedance to reverse feed. I did not notice any degradation of the airband signal by using this arrangement.@ad cd, Lets take this scenario in to consideration. Lets say someone has two antennas on there roof, a CoCo or other design ADS-B antenna, and a discone. Now I know my CoCo receives FM/433mhz and 800mhz trunked systems loud and clear, much better than a set of rabbit ears with the filters removed. Now lets say the person were to add a 1090mhz coild as you did before the discone, this would make it so the ADSB antenna was the only one letting 1090mhz through, giving optimal ADS-B performance correct? But wouldn't the discone get loaded down with all the other out of band signals the CoCo antenna is receiving and cause problems for the discone? Do you get degraded air band reception with your set up than if you were to only run the air band and antenna by itself?