Chuck & Jeff, Yes you are correct...2 x 50 Ohm load paralleled to give 25 Ohm then thru 35 Ohm 1/4 wl cable will transform back to 50 Ohms and then any 50 Ohm cable can be attached.
Most multi-dipole antennas I've seen use 72 Ohm cable coming off each dipole. 50 thru 72 Ohm 1/4 wl give 100 Ohms and parallel 2 of these to get 50 Ohms. I've seen the DB224 in this configuration. Of course there they have a second harness to couple 2 sets of dipoles for 4 bay. Another monkey wrench in this discussion. The use of 72 Ohm cable would take less cable, but use of 35 Ohm cable would be simpler since only one cable critical length. 73, ron, n9ee/r >From: Chuck Kelsey <[EMAIL PROTECTED]> >Date: 2008/03/06 Thu AM 10:36:40 CST >To: [email protected] >Subject: Re: [Repeater-Builder] Re: DB 212-2 Harness info. > >I agree with Jeff. The lines to each element are 50-ohm. They can be any >length, but must be equal in length. Connect to the tee. Then a 1/4-wave >section of 35-ohm cable. This brings things back to 50-ohms. At that point >connect any length of 50-ohm transmission cable. > >Chuck >WB2EDV > >----- Original Message ----- >From: "Jeff DePolo" <[EMAIL PROTECTED]> >To: <[email protected]> >Sent: Thursday, March 06, 2008 11:19 AM >Subject: RE: [Repeater-Builder] Re: DB 212-2 Harness info. > >>> What this does with antenna element at 50 Ohms then 1/4 wl >>> down the 35 Ohm cable it looks close to 100 Ohms looking into >>> this cable. >> >> No, that's not right. If the element were 50 ohms and you attached 1/4 >> wave >> of 35 ohm cable, you would transform it down to 25 ohms, not up to 100 >> ohms. >> You could transform 50 UP to 100 via a 75 ohm odd-quarterwave cable. >> >>> The length of the 50 Ohm coax going from the tx/rx to this >>> antenna input does not matter for SWR or impedance. Only >>> concern would be length and loss of 50 Ohm cable. >> >> Just to be clear, the length of the 50 ohm cable doesn't matter at the >> input >> to the antenna, but it DOES matter within the harness itself even if the >> cable isn't being used as a transformer. The bays have to be fed in-phase >> otherwise uptilt/downtilt and elevation pattern distortion will occur. >> >> --- Jeff WN3A >> >> >> >> >> >> >> >> >> Yahoo! Groups Links >> >> >> >> > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
