Re: Mount an Arrow on rotator with 2m vertical orhorizontal
Hi Douglas,
Using two identical 50 ohm coax lenght you can't transform each 50 ohm antenna impedance into 100 ohm but if you connect both 50 ohm coax cables to a T connector than the resulting impedance at the common output of the T connector will be 25 ohm i.e. two 50 ohm impedances in parallel and your radio will see a VSWR of 50/25 = 2 and this is the reason it will not work !
BTW if you connect the above 25 ohm impedance to the input of a 1/4 electrical wavelenght long coax cable of 36 ohm impedance than at the output of it you will get an impedance of 36^2 / 25 = 52 ohm toward the main feed line with a good VSWR of about 1 in TX and RX
To build a 1/4 electrical wavelengt long of a transmission line of 36 ohm impedance you can connect in parallel two 1/4 electrical wavelenght of 75 ohm coax cable like RG59 or RG11 i.e. 34,13 centimeters or 13,38 inches long for 145 MHz
BTW in this situation if both antennas are mounted in parallel one Vertical and the other one Horizontal and if the elements are mounted on the same plain with respect to the space than the resulting polarization of the radiated field can be at 45 degrees like \ or at 135 degrees like / depending at wich side of the dipoles the inner conductors of the 50 ohm feed lines are connected.
73" de
i8CVS Domenico
 Original Message  From: "Douglas Phelps" [email protected] To: "R.T.Liddy" [email protected]; [email protected] Sent: Tuesday, April 16, 2013 8:31 PM Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m vertical orhorizontal
Any reason why, using identical coax lengths, you could not transform the impedance to 100 ohms and then use a T connector to sum both antenna signals and achieve 50 ohms to the radio? I know Transmit power will be 3 dB down at either antenna but is there any reason it will not work? Any antenna gurus out there?
Domenico, There are two solutions to use coax to combine two 50 Ohm antennas. 70.7 Ohm cable (50 to 100) [Two 50 ohm antennas transformed by two lines to 100 Ohms each, in parallel = 50 Ohms] and your suggestion using 35.4 Ohm cable section (25 to 50) = [Two 50 ohm antennas connected in parallel = 25 Ohms, transformed to 50 Ohms]
The interesting part is you do not save anything when using 75 Ohm coax as 1/4 wave sections (two in parallel =37.5 Ohms) VS two separate 75 ohm sections one to each antenna.
Art, KC6UQH
Original Message From: [email protected] [mailto:[email protected]] On Behalf Of i8cvs Sent: Wednesday, April 17, 2013 5:00 AM To: Douglas Phelps; R.T.Liddy; Amsat  BBs Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Hi Douglas,
Using two identical 50 ohm coax lenght you can't transform each 50 ohm antenna impedance into 100 ohm but if you connect both 50 ohm coax cables to a T connector than the resulting impedance at the common output of the T connector will be 25 ohm i.e. two 50 ohm impedances in parallel and your radio will see a VSWR of 50/25 = 2 and this is the reason it will not work !
BTW if you connect the above 25 ohm impedance to the input of a 1/4 electrical wavelenght long coax cable of 36 ohm impedance than at the output of it you will get an impedance of 36^2 / 25 = 52 ohm toward the main feed line with a good VSWR of about 1 in TX and RX
To build a 1/4 electrical wavelengt long of a transmission line of 36 ohm impedance you can connect in parallel two 1/4 electrical wavelenght of 75 ohm coax cable like RG59 or RG11 i.e. 34,13 centimeters or 13,38 inches long for 145 MHz
BTW in this situation if both antennas are mounted in parallel one Vertical and the other one Horizontal and if the elements are mounted on the same plain with respect to the space than the resulting polarization of the radiated field can be at 45 degrees like \ or at 135 degrees like / depending at wich side of the dipoles the inner conductors of the 50 ohm feed lines are connected.
73" de
i8CVS Domenico
 Original Message  From: "Douglas Phelps" [email protected] To: "R.T.Liddy" [email protected]; [email protected] Sent: Tuesday, April 16, 2013 8:31 PM Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m vertical orhorizontal
Any reason why, using identical coax lengths, you could not transform the impedance to 100 ohms and then use a T connector to sum both antenna signals and achieve 50 ohms to the radio? I know Transmit power will be 3 dB down at either antenna but is there any reason it will not work? Any antenna gurus out there?
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSATNA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsatbb
Hello Domenico, Art and the bb, My comment here is with the ARROWS antennas.
I think one thing is overlooked here. We are dealing with two antennas on different frequencies.
And yes in this it may work since 435 MHz is 3 times the 145 MHz. So 1 quarter wavelength on 145 MHz becomes 3 quarter wavelength on 435 MHz. Therefore it may work impedance wise.
However there may be a problem with coupling between the two frequency bands.
73 OZ1MY/Ib
Oprindelig meddelelse Fra: [email protected] [mailto:[email protected]] På vegne af Art McBride Sendt: 20 April 2013 19:47 Til: 'i8cvs'; 'Douglas Phelps'; 'R.T.Liddy'; 'Amsat  BBs' Emne: [amsatbb] Re: Mount an Arrow on rotator with 2mverticalorhorizontal
Domenico, There are two solutions to use coax to combine two 50 Ohm antennas. 70.7 Ohm cable (50 to 100) [Two 50 ohm antennas transformed by two lines to 100 Ohms each, in parallel = 50 Ohms] and your suggestion using 35.4 Ohm cable section (25 to 50) = [Two 50 ohm antennas connected in parallel = 25 Ohms, transformed to 50 Ohms]
The interesting part is you do not save anything when using 75 Ohm coax as 1/4 wave sections (two in parallel =37.5 Ohms) VS two separate 75 ohm sections one to each antenna.
Art, KC6UQH
Original Message From: [email protected] [mailto:[email protected]] On Behalf Of i8cvs Sent: Wednesday, April 17, 2013 5:00 AM To: Douglas Phelps; R.T.Liddy; Amsat  BBs Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Hi Douglas,
Using two identical 50 ohm coax lenght you can't transform each 50 ohm antenna impedance into 100 ohm but if you connect both 50 ohm coax cables to a T connector than the resulting impedance at the common output of the T connector will be 25 ohm i.e. two 50 ohm impedances in parallel and your radio will see a VSWR of 50/25 = 2 and this is the reason it will not work !
BTW if you connect the above 25 ohm impedance to the input of a 1/4 electrical wavelenght long coax cable of 36 ohm impedance than at the output of it you will get an impedance of 36^2 / 25 = 52 ohm toward the main feed line with a good VSWR of about 1 in TX and RX
To build a 1/4 electrical wavelengt long of a transmission line of 36 ohm impedance you can connect in parallel two 1/4 electrical wavelenght of 75 ohm coax cable like RG59 or RG11 i.e. 34,13 centimeters or 13,38 inches long for 145 MHz
BTW in this situation if both antennas are mounted in parallel one Vertical and the other one Horizontal and if the elements are mounted on the same plain with respect to the space than the resulting polarization of the radiated field can be at 45 degrees like \ or at 135 degrees like / depending at wich side of the dipoles the inner conductors of the 50 ohm feed lines are connected.
73" de
i8CVS Domenico
 Original Message  From: "Douglas Phelps" [email protected] To: "R.T.Liddy" [email protected]; [email protected] Sent: Tuesday, April 16, 2013 8:31 PM Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m vertical orhorizontal
Any reason why, using identical coax lengths, you could not transform the impedance to 100 ohms and then use a T connector to sum both antenna signals and achieve 50 ohms to the radio? I know Transmit power will be 3 dB down at either antenna but is there any reason it will not work? Any antenna gurus out there?
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSATNA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsatbb
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSATNA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsatbb
Hi Art, KC6UQH
Feeding a 50 ohm antenna with a odd numbar of 1/4 electrical wavelenght of 75 ohm coax cable you transform the 50 ohm antenna impedance into 100 ohm and connecting two 100 ohm impedances in parallel you get again 50 ohm to supply the system main fedline to TX and RX but using this solution the VSWR into the 75 ohm coax cables is 75/50 = 1.5 and this VSWR represent losses particularly at high frequencies from 435 MHz and up to 1296 MHz
On the other side feeding two 50 ohm antennas with the same lenghts of 50 ohm coax cables in parallel you get a 25 ohm impedance to be transformed again into 50 ohm using a matching line of 37.5 ohm 1/4 electrical wavelenght long made with two pieces of coax cable 1/4 electrical wavelenght long but in this solution the VSWR into both 50 ohm feeding lines will be a good 1 to 1 and the losses are not very high so that this second solution seems to be preferable.
The 37.5 ohm Zo impedance power divider can be professionally built in air using two sections of round copper tubing 1/4 wavelenght long using the following formula:
Zo = 138 log (D/d) 10
where D is the inside diameter of the outer tubing and d is the outside diameter of the inner tubing.
In this solutions the RF losses are less than using two sections of 75 ohm coax cables in parallel each 1/4 electrical wavelenght long so that this round copper tubing power divider solution seems to be preferred and it is that I currently use up to 1296 MHz
73" de
i8CVS Domenico
 Original Message  From: "Art McBride" [email protected] To: "'i8cvs'" [email protected]; "'Douglas Phelps'" [email protected]; "'R.T.Liddy'" [email protected]; "'Amsat  BBs'" [email protected] Sent: Saturday, April 20, 2013 7:47 PM Subject: RE: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Domenico, There are two solutions to use coax to combine two 50 Ohm antennas. 70.7 Ohm cable (50 to 100) [Two 50 ohm antennas transformed by two lines to 100 Ohms each, in parallel = 50 Ohms] and your suggestion using 35.4 Ohm cable section (25 to 50) = [Two 50 ohm antennas connected in parallel = 25 Ohms, transformed to 50 Ohms]
The interesting part is you do not save anything when using 75 Ohm coax as 1/4 wave sections (two in parallel =37.5 Ohms) VS two separate 75 ohm sections one to each antenna.
Art, KC6UQH
Original Message From: [email protected] [mailto:[email protected]] On Behalf Of i8cvs Sent: Wednesday, April 17, 2013 5:00 AM To: Douglas Phelps; R.T.Liddy; Amsat  BBs Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Hi Douglas,
Using two identical 50 ohm coax lenght you can't transform each 50 ohm antenna impedance into 100 ohm but if you connect both 50 ohm coax cables to a T connector than the resulting impedance at the common output of the T connector will be 25 ohm i.e. two 50 ohm impedances in parallel and your radio will see a VSWR of 50/25 = 2 and this is the reason it will not work !
BTW if you connect the above 25 ohm impedance to the input of a 1/4 electrical wavelenght long coax cable of 36 ohm impedance than at the output of it you will get an impedance of 36^2 / 25 = 52 ohm toward the main feed line with a good VSWR of about 1 in TX and RX
To build a 1/4 electrical wavelengt long of a transmission line of 36 ohm impedance you can connect in parallel two 1/4 electrical wavelenght of 75 ohm coax cable like RG59 or RG11 i.e. 34,13 centimeters or 13,38 inches long for 145 MHz
BTW in this situation if both antennas are mounted in parallel one Vertical and the other one Horizontal and if the elements are mounted on the same plain with respect to the space than the resulting polarization of the radiated field can be at 45 degrees like \ or at 135 degrees like / depending at wich side of the dipoles the inner conductors of the 50 ohm feed lines are connected.
73" de
i8CVS Domenico
 Original Message  From: "Douglas Phelps" [email protected] To: "R.T.Liddy" [email protected]; [email protected] Sent: Tuesday, April 16, 2013 8:31 PM Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m vertical orhorizontal
Any reason why, using identical coax lengths, you could not transform the impedance to 100 ohms and then use a T connector to sum both antenna signals and achieve 50 ohms to the radio? I know Transmit power will be 3 dB down at either antenna but is there any reason it will not work? Any antenna gurus out there?
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSATNA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsatbb
Domenico, Loss for a 1/4 wave resonant line is small. RG 4121/2 5/8 and 3/4 inch 75 Ohm line for CATV is very low loss. If you build your own Coax the impedance should be 35.4 Ohms for your preferred match.
73, Art
Original Message From: i8cvs [mailto:[email protected]] Sent: Saturday, April 20, 2013 3:29 PM To: [email protected]; 'Douglas Phelps'; 'R.T.Liddy'; 'Amsat  BBs' Subject: Re: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Hi Art, KC6UQH
Feeding a 50 ohm antenna with a odd numbar of 1/4 electrical wavelenght of 75 ohm coax cable you transform the 50 ohm antenna impedance into 100 ohm and connecting two 100 ohm impedances in parallel you get again 50 ohm to supply the system main fedline to TX and RX but using this solution the VSWR into the 75 ohm coax cables is 75/50 = 1.5 and this VSWR represent losses particularly at high frequencies from 435 MHz and up to 1296 MHz
On the other side feeding two 50 ohm antennas with the same lenghts of 50 ohm coax cables in parallel you get a 25 ohm impedance to be transformed again into 50 ohm using a matching line of 37.5 ohm 1/4 electrical wavelenght long made with two pieces of coax cable 1/4 electrical wavelenght long but in this solution the VSWR into both 50 ohm feeding lines will be a good 1 to 1 and the losses are not very high so that this second solution seems to be preferable.
The 37.5 ohm Zo impedance power divider can be professionally built in air using two sections of round copper tubing 1/4 wavelenght long using the following formula:
Zo = 138 log (D/d) 10
where D is the inside diameter of the outer tubing and d is the outside diameter of the inner tubing.
In this solutions the RF losses are less than using two sections of 75 ohm coax cables in parallel each 1/4 electrical wavelenght long so that this round copper tubing power divider solution seems to be preferred and it is that I currently use up to 1296 MHz
73" de
i8CVS Domenico
 Original Message  From: "Art McBride" [email protected] To: "'i8cvs'" [email protected]; "'Douglas Phelps'" [email protected]; "'R.T.Liddy'" [email protected]; "'Amsat  BBs'" [email protected] Sent: Saturday, April 20, 2013 7:47 PM Subject: RE: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Domenico, There are two solutions to use coax to combine two 50 Ohm antennas. 70.7 Ohm cable (50 to 100) [Two 50 ohm antennas transformed by two lines to 100 Ohms each, in parallel = 50 Ohms] and your suggestion using 35.4 Ohm cable section (25 to 50) = [Two 50 ohm antennas connected in parallel = 25 Ohms, transformed to 50 Ohms]
The interesting part is you do not save anything when using 75 Ohm coax as 1/4 wave sections (two in parallel =37.5 Ohms) VS two separate 75 ohm sections one to each antenna.
Art, KC6UQH
Original Message From: [email protected] [mailto:[email protected]] On Behalf Of i8cvs Sent: Wednesday, April 17, 2013 5:00 AM To: Douglas Phelps; R.T.Liddy; Amsat  BBs Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m verticalorhorizontal
Hi Douglas,
Using two identical 50 ohm coax lenght you can't transform each 50 ohm antenna impedance into 100 ohm but if you connect both 50 ohm coax cables to a T connector than the resulting impedance at the common output of the T connector will be 25 ohm i.e. two 50 ohm impedances in parallel and your radio will see a VSWR of 50/25 = 2 and this is the reason it will not work !
BTW if you connect the above 25 ohm impedance to the input of a 1/4 electrical wavelenght long coax cable of 36 ohm impedance than at the output of it you will get an impedance of 36^2 / 25 = 52 ohm toward the main feed line with a good VSWR of about 1 in TX and RX
To build a 1/4 electrical wavelengt long of a transmission line of 36 ohm impedance you can connect in parallel two 1/4 electrical wavelenght of 75 ohm coax cable like RG59 or RG11 i.e. 34,13 centimeters or 13,38 inches long for 145 MHz
BTW in this situation if both antennas are mounted in parallel one Vertical and the other one Horizontal and if the elements are mounted on the same plain with respect to the space than the resulting polarization of the radiated field can be at 45 degrees like \ or at 135 degrees like / depending at wich side of the dipoles the inner conductors of the 50 ohm feed lines are connected.
73" de
i8CVS Domenico
 Original Message  From: "Douglas Phelps" [email protected] To: "R.T.Liddy" [email protected]; [email protected] Sent: Tuesday, April 16, 2013 8:31 PM Subject: [amsatbb] Re: Mount an Arrow on rotator with 2m vertical orhorizontal
Any reason why, using identical coax lengths, you could not transform the impedance to 100 ohms and then use a T connector to sum both antenna signals and achieve 50 ohms to the radio? I know Transmit power will be 3 dB down at either antenna but is there any reason it will not work? Any antenna gurus out there?
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSATNA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsatbb
participants (3)

Art McBride

i8cvs

Ib Christoffersen