6

Puh! That's a big one you're planning: Most circulators are passive, magnetic material circulators: These circulators are basically a three-port resonant cavity in a cylindric shape, where the cavity is filled with ferrimagnetic material, typically special ferrite disks. The electromagnetic properties of magnetized ferrite are used to break up the ...


6

Yes, it will work with the proper attention to details. I have done the same in the past at two repeater sites to take advantage of the coverage of the dual band antenna. Do take care as the third harmonic of two meter frequencies can come close to 70 cm frequencies. You will want to plan your frequencies to keep as much separation as possible. Making the ...


5

Like you, I modeled your diplexer in LTSpice, but I don't find the results to be acceptable. At 147-MHz, the input impedance is 87$\Omega$; at 443-MHz, it's 24$\Omega$. Also, the crossover frequency is about 350-MHz, which seems too high. Tonne Software offers Diplexer Designer to address your requirement. Creating a low-pass / high-pass design with a ...


5

You have soldered a 68nH inductor instead of 100nH! Maybe the layout and the wiring also play a key role. Here's a vintage commercial one. It's quite compact. The size, inclusive of the coaxial sockets, is 4" x 2" x 1". Here's the schematic. Tin plating is observed inside the enclosure. There is no PCB and the wiring is point-to-point. Connections to ...


5

A circulator can probably be constructed from coaxial cable. However, you will also need ferrite and magnets. From https://wa8dbw.ifip.com/Circulator.html : A circulator is best thought of as a "Magic Box" containing three transmission lines spaced 120 degrees apart. These transmission lines are placed between two disks of ferrite material. On the other ...


3

I've got a bit of knowledge of military radio systems. The military is not especially fond of ground based repeater systems, especially in any environment where they would need to be mobile, partially for the reasons you mention. They're bulky, finicky and take time to set up. More importantly though, losing one to enemy action or just bad luck instantly ...


2

The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal. Indeed. The notch filter in the transmit side is instead to protect the receiver from the transmitter. As well as the familiar harmonics and spur signals generated on specific frequencies by the transmitter it also produces broadband noise centred on ...


2

The added capacitance of the RG58 stubs may also be an issue. I suggest using flat copper strip instead between the port connectors and the PCB. While you can probably get away with SO239's for just 2m, N connectors (or similar UHF connectors) are really mandatory here.


2

In the absence of test equipment there is no way to know for certain what went wrong, or what to do about it. The duplexer sounds like the most likely culprit, but the problem could be something else, like inadequate shielding in the receiver. If you ask around, maybe someone in your area has the necessary test equipment and wouldn't mind helping.


1

The transmitter doesn't need protection from the receiver, because the receiver doesn't transmit any signal. Perhaps not, but consider: The transmitter makes broadband noise and intermodulation products that may fall on the receive frequency. More isolation is better. And, The transmitter should ideally also not load the antenna at the receive frequency. ...


1

There is a trick to balance the notch tuning johannsen cap adjustment with the coupling ring loops to meet the required rejection per side with minimum insertion loss. I believe I tuned mine to reject 40-45dB rejection per cavity at max. First, I would get the pass rod approximately at the pass frequency, then tune notch under cap. If too deep or shallow a ...


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