1 How close in frequency to the tuned pair? Normally no, it will only work for the frequencies it is tuned to... Especially with a notch only system like a mobile duplexer, which might only have maybe 40 or 50 dB isolation to start with... You make up the difference by having a 5 MHz difference in the frequencies.
2. You should be concerned with both the SWR between the transmitter and the duplexer and the duplexer and the antenna.. The first is an indication of the band pass characteristics of the duplexer at the frequency in use while the second tells you whether the antenna and feedline is properly matched ...Actually you should be concerned with mismatches betweem the receiver and the duplexer for the same reason but you need a diffferent way to evaluate that. 3. Ideally you should use the best tranmission line you can afford between the duplexer and the antenna... RG 58 is very lossy at UHF...There are less lossy feedlines of similar small size since concealment is one of your issues, and these would probably not be a major issue for a 5 meter length.... Also remember that the lines coming from both the transmitter and the receiver should be double shielded to minimize desense... I normally use RG-142... In your case maybe a short run of RG-142 double shielded coax from the duplexer to the antenna might be appropriate, but I'll leave that end of the discussion to someone else who might have a different or bettter idea. Good luck Dave WB2FTX ----- Original Message ----- From: tait700 To: [email protected] Sent: Saturday, April 04, 2009 10:12 AM Subject: [Repeater-Builder] UHF Mobile Duplexer Questions Hello, I am new to Repeater Building and was wondering if someone Knowledgeable would be able to answer Three Questions for me ? 1, With a Duplexer tuned to say 467.00 Low side and 477.00 high side will the duplexer only function at those Frequencies, i.e if the system has another pair of Tx / Rx frequencies that are close to the tuned pair is the duplexer able to handle both sets or only the ones that is is specially tuned for ? 2. When the system is completed and the final vswr readings are being taken is the vswr meter inserted between the Duplexer and the Antenna or between the Duplexer and the Tx radio ? I understand that when checking the vswr on a normal conventional radio / antenna system the reading is taken on both the highest and lowest Tx frequency, and any adjustments made to give the best result at the centre of the two. Is the procedure the same for a duplexer with the checking frequency being the midle of the Tx / Rx seperation ? 3. Could someone possibly indicate how much signal loss i could reasonably expect with the insertion of the Duplexer to the system. I have a very short cable run from the Duplexer to the single antenna < 5M and am running RG58U/C. I realize i should be running Hardline to minimize signal loss but we have very strict building codes here which prohibit any type extended vertical antennas and i have had to conceal its location requiring a convoluted path for the feedline to the antenna. Sorry for the longwinded post, i would be very grateful for any and all info people could provide on the above. Thank you for your help, Regards, Tait 700 ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.0.238 / Virus Database: 270.11.41/2040 - Release Date: 04/03/09 17:54:00
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