On another occasion I found the center conductor of one pigtail wasn't even soldered to the circuit board during manufacture the shield was, how could the assembler miss that? On another occasion the coaxial cable pulled out of the metal body. On the other hand I have never had a physical problem with the ones that have real coaxial connectors mounted in the diplexer metal housing. Note that every manufacturer of ham-grade units uses nickel or chrome plated connectors I have seen a Comet triplexer that was shipped with coax pigtails, but now has silver plated female N connectors in all four locations.
It's being used on a remote base system: the 2m is a GM channel-steered remote base radio, the UHF is the user repeater, and the MHz port feeds a control receiver. Duplexers are in-band units that are made from multiple cavities, so therefore we need to know a little about cavities A cavity, depending on how it is made and used can be a peak filter or a notch filter. Some cavities have the connectors in the top, others have the connectors on the side.
Multiple cavities in series can collectively increase the peak height or the notch depth. This additive characteristic is what makes a duplexer possible. The normal purpose of a duplexer is to allow the simultaneous operation of a receiver and a transmitter in the same frequency band on the same antenna.
Duplexers are made from multiple cavities arranged so that the peak or notch from each one is added to the previous one and the next one by means of critical length cables.
Unfortunately, saying "duplexer" is like saying "car". They come in various types, makes, models, and performance levels. Some are notch-only, others are notch-pass.
There are 3-cavity, 4-cavity, 5-cavity, and there are 6-cavity models more cavities give a higher level of receiver-to-transmitter isolation, but at a cost of increased insertion loss and I have seen both a 7-cavity and an 8-cavity unit. There are also special purpose assemblies based on duplexers. In general, the higher the RF level at a site i.
I've also seen a 8-cavity 4-port duplexer it was a custom order that allowed a And you may not need a duplexer at all if you run a split site system at a low RF level site. Depending on circumstances even a single site system can be built with no duplexer at all see the "Some thoughts on Repeater Receiver-to-Transmitter Isolation" article elsewhere on the Antenna page.
And to continue the used car analogy above, used duplexers can have problems just like used cars. Unless you trust the used duplexer seller you will want to have your radio mechanic test it out before you buy it.
As just one example - many duplexers have a variable capacitor as part of the tuned circuit the "loop" on each port. Usually these are a precision glass vacuum variable capacitor. And the effort involved in replacing one can be anything from simple to outrageous depending on how the cavity is built.
Duplexers expect to see a 50 ohm load on every port, and many transmitters, many receivers and some antennas are not. A duplexer is 50 ohms only at resonance , anywhere else it is reactive. If it is not, the most common way to "fix" the problem is to use a "magic" length cable - but the right way is to fix the radio so it is 50 ohms.
The proper way to tune a cavity or a duplexer is to use 6 dB or 10 dB 50 ohm pads between the test equipment and the cavity or endmost duplexer can, as that ensures that pad "masks" any nonohm-impedance in your test equipment and ensures that the duplexer is really tuned to precisely 50 ohms.
Many folks that take a duplexer that is tuned on the bench with 6 dB pads on each port to guarantee a 50 ohm environment and then install it in a system discover that the duplexer is "mistuned" - that they have to make adjustments to get the same performance that they had on the bench. The transmitter can be fixed with a "Z-Matcher". Then retune the duplexer. Once the duplexer is tuned properly it should NOT need ANY adjustments from the bench to the site except for the bumpy mile-long four wheel drive road - and that's why you take the pads and the service monitor with you to verify the tuning on site.
And you try to drive that 4wd road "gently". A posting on repeater-builder a while back made the comment that the GE MASTR II UHF transmitter output impedance was mostly 50 ohms resistive, but with a capacitive or inductive component whose value depended on what company made the output transistors and this characteristic is not limited to GE equipment.
In the early days of the MASTR II large fleet operators were having an unusually high number of station and repeater power amplifier failures. One large user that I am aware of had eight repeaters and was losing roughly one PA per month.
After GE had several engineers investigate the problem they came up with a two-pronged fix. Solid state power amplifiers do not like reactive loads, and the engineers found that the best solution was a pi-network output matching stage followed by a circulator to protect the output device s from an unmatched load. GE had Decibel Products develop a "Z Matcher" device which functioned as the output tank circuit that the transmitter designer had left out. The second prong of the field fix was that GE ended up buying a circulator for each transmitter and this solved the rest of the problem this situation is why the Motorola MICOR line has a factory-installed circulator in every PA deck - even in the mobiles!
As mentioned above, every circulator must be followed by a low pass filter some installations use a pass cavity, which itself might be separate or part of a pass-notch duplexer.
Unmatched loads did not start with solid state PA decks. Feedlines over the years have included 35 ohms, 50 ohms, 75 ohms, 93 ohms, ohms and ohms. As mentioned, one way to transform impedances is to use a "magic" length of the right impedance of coax as a matching transformer. The cable length between the end cavity and the transmitter is NOT supposed to be critical, and if it is then you have an impedance problem. While the most common situation is between the transmitter power amplifier and the duplexer, the same situation can happen between the receiving antenna and the receiver, or between the duplexer and the receiver Matching the transmitter to the duplexer is covered in this article Cabling lengths between the Duplexer and Radio Set.
Despite the article title, there is a lot of impedance matcher usually called Z-matcher info in there. The closeup photos show how GE simply replaced the station antenna relay with the Z-matcher daughter board prior to the Z-Matcher it had been replaced with a jumper.
The schematic to the GE Z-Matcher is here. It's part of LBIG. The tuneup info for the DB Products Z-matchers can be found here. As said above a duplexer is made up of a number of cavities and a number of critical length cables beteeen them.
Infrastructure Hardware. Power Systems. Test Equipment. Wi-Fi Networking Equipment. Understanding Antenna Duplexers. What is a Duplexer? Duplexers must: Be designed for operation in the frequency band used by the receiver and transmitter and must be capable of handling the output power of the transmitter.
Antenna diplexer applications Antenna diplexers find many uses. In view of the size and cost of the antennas they may have a single vertical antenna and they may want to combine the signals from several transmitters to feed into the antenna. As they are on different frequencies, it is possible to use a diplexer to combine the signals and use a single feed.
Enabling a multiband transmitter to use different antennas according to frequency : Some transmitters like some ham radio transmitters can cover very wide ranges of bands - for ham radio transmitters there is a growing trend towards transmitters covering HF and VHF bands. They may even extend into the UHF region. Allowing single feeder to be used for multiple feeds, e. The signals from he antennas can be combined at the antenna end using diplexer, and a second diplexer at the point of use to route the signals to the radio and television.
Diplexer definition: A diplexer is a device that enables different devices to share a common feeder or resource. It typically consists of filters Low Pass, High Pass or Band Pass at different frequencies connected to to allow the sharing.
Duplexer definition: A duplexer is a device that allows duplex operation a device to allow transmitters and receivers on slightly different frequencies on the same band to use the same antenna.
It isolates the transmitter from the receiver, giving sufficient isolation for them to operate at the same time. A circulator is an ideal example of a duplexer. Basic antenna diplexer concepts There are a number of ways of implementing RF diplexers.
RF diplexer filter requirements When designing an antenna diplexer a number of parameters must be considered. Band pass filters Under some circumstances band pass filters may be used. Shopping on Electronics Notes Electronics Notes offers a host of products are very good prices from our shopping pages in association with Amazon. Note: Electronics Notes receives a small commission on sales at no cost to you.
Selected Video What is a Spectrum Analyzer? How to Adjust Scope Probe Compensation.
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