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KB2VXA > TECH 02.12.03 00:08l 51 Lines 2381 Bytes #999 (0) @ WW
BID : 16352_WT3V
Read: DB0FHN GUEST OE7FMI
Subj: Re: G8MNY > Homebrew Duplexers
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<WB0TAX<N1UAN<WB1CHU<K1UGM<
W1ON<W1ON-5<K1UOL<K1UOL<WA2PNU<KC2COJ<WT3V
Sent: 031201/1101 16352@WT3V.#CNJ.NJ.USA.NOAM $:16352_WT3V
From: KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
To : TECH@WW
Hi John and readers,
One thing I should point out at the outset is the common misuse of terms.
I see it all the time and again in your bulletin. You use the term
"duplexer" in the subject field while using "diplexer" in the text body.
That's a bit confusing so I shall explain. A duplexer allows repeater
operation by passing the input and output signals simultaniously through
extremely narrow tuned cavity filters, thereby allowing full duplex
operation. A diplexer allows simultanious operation of two transmitters
operating on two slightly separated frequencies on a single antenna. A
variation allows dual band operation of two tranceivers on a single
antenna or dual antennas on a single tranceiver simultaniously depending
on which direction it is connected.
No I can understand some of the resoning behind using one for 2M/70cM
operation but not all. In the case of single band antennas (which with
the exception of beams) is redundant inasmuch as a @M antenna works well
on 70cM. Darn, another typo, make that 2M. A quarter wave on 144Mc is a
3/4 wave on 432Mc and presents a 50 Ohm load, so do odd multiples making
a 70cM antenna redundant. This is particularly useful for mobile
operation, using a 1/4 wave 2M antenna saves cluttering the vehicle with
antennas and the needless expense of a so called "dual band" antenna.
One practical application is separate 2M and 70cM tranceivers feeding a
single antenna so a station could employ two operators during a contest.
Beyond this I see little use for such a diplexer, especially since one
injects considerable signal loss making it a distinct disadvantage for
weak signal work.
Now if I have gone wrong somewhere I would appreciate someone explaining
the advantages of using one. Meanwhile I'll continue to use a multiband
tranceiver and one separate with a coaxial cavity switch and a multiband
antenna. Oh yes, other antennas are envisioned for future weak signal
work, but I shall use coaxial cavity switching for minimal signal loss.
73 de Warren, KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
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Message timed by cesium laser: 11:10 on 2003-Dec-01 GMT
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