[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

*Subject*: RE: [amsat-bb] Re: 92 ohm line*From*: "Brown, Gerald" <grbrown@xxxxxxxxxxx>*Date*: Tue, 02 Mar 1999 07:52:12 -0600

John's suggestion of using 2 sections of RG-58 (the second example) is sound. It maintains the balanced feed arrangement between the loops and may negate the anomaly I noted in the article dealing with the unbalanced feed arrangement. If anyone tries this out, let me know how it works. Just as info on the same topic, I have successfully used the configuration in John's first example below as a matching transformer when feeding two 50 Ohm antennae (common application for sat work). I find it far simpler and more accurate than the methods presented in most of the literature. My particular application was two 70 cm quagi's, physically offset for RHCP. Using 50 Ohm cable from each antenna (allows you to match the antenna with an swr meter), run any length--but the same length--to a 50 Ohm coaxial tee. This will give you 25 Ohms at the output of the tee. From the output of the tee connect two 1/4 wl sections of 75 Ohm coax (centers soldered together). This coaxial transformer has a nominal impedance of 37.5 Ohms, the exact geometric mean needed to transform 25 Ohms back up to 50 Ohms at the output. In fact, by careful pruning of the 37.5 Ohm line, you can get an exact SWR match to 50 Ohms--not something you can do when trying to use the "conventional" method of running 75 Ohm cable from the antennas to the tee. 50 Ohm cable Ant 1 o------------------- | 1/4 wl 37.5 Ohms coax tee -> |- ================== --------------------------- | 50 Ohm cable to rig Ant 2 o------------------- 50 Ohm cable 73, Jerry --------------------------------------------------------- (KD6PAG writes) > OK, here are the two cases, the first one mentioned > > ----------------------------- > o-*-----| RG58 |----*--o > | --*----------------------------*- | > | / \ | 25 > | | ------------------------------ | | ohms > \-|--| RG58 |-|--/ > o----*--*----------------------------*-*-----o > > > And the second, where the shields are soldered together on each end: > > - -------------------------------- > 0------| RG58 |-----0 > *----------------------------------* > | | 100 > | | ohms > *----------------------------------* > O------| RG58 |-----O > - -------------------------------- > > > [ARRL Antenna Book (16th Ed.), p. 24-21] > > And note that *i* didn't use the term 'in parallel' here. I don't know > what > you would call which. > > Of course, two lengths of RG59 gives about 150 ohms, as would two lengths > of TV twinlead in parallel might (but i'd be real concerned about > proximity > effects in that case). > > -- KD6PAG (Networking Old-Timer, "RF newbie") > ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

- Prev by Date:
**Re: Laser Satellite Comms** - Next by Date:
**Re: [sarex] Re: Laser Satellite Comms** - Prev by thread:
**Re: Laser Satellite Comms** - Next by thread:
**WiSP Updates** - Index(es):