Isolator
Isolators are a safety device that prevents RF from bouncing back and damaging the Tx board. They are included as standard on 2&4 port combiners and are raised off the shelf as being next to metal affects their performance. The arrow on the label shows the direction of RF. If the isolator starts to heat up then it’s been installed the wrong way. They are very low loss but it is good practice to have one on every Tx circuit.
ZAPD-1
ZAPDs are a 50/50 splitters but can’t handle much power. They are perfect for RF splitters on Rx circuits but are unsuitable as a combiner. They can handle about 1W safely.
Hybrid Combiner
A Hybrid coupler can function as either an RF splitter or combiner. Ports 1&2 are inputs and ports 3&4 outputs. They work by taking 50% of ports 1&2, combine them and send the RF out of port 3 with the same going out of port 4. When using them as a combiner you’ll need to attach a dummy load to either port 3&4.
Power Splitter
These are 50/50 splitters but unlike the ZAPD-1s they can handle more power and are suitable for splitting Tx as well as Rx.
Directional Couplers (sniffs)
These are more of a 90/10 splitter. 90% goes to the “out” port and 10% goes to the sniff port. As the name suggests they only work one way.
Dummy Load
These absorb RF energy and the maximum amount of power they can absorb is rated on them. The more energy they absorb the hotter they are so be careful when handling them on live rigs. If you are planning to use them for long periods consider installing a fan close by if, they are in an enclosed space to keep them cool.
Band Pass Filter
As the name says this, will pass all RF between two frequency bands and reject everything else. The size of the pass band will vary depending on how many chambers the filter has as well as the make. To tune a filter you will need to adjust the screw heads (the 3 on the left hand side in this case). Be aware that some filters may require you to release a securing nut prior to tuning. In which case simply loosen it a few turns but do not remove the nut.
Band Stop (Notch) Filter
Band stop filters do the opposite of a band pass filter. We use them to create duplexer by adjusting the high and low outputs to “notch” each other out. For example if you were tuning it for the receive circuit you would tune the filter so the middle of the “notch” where the base transmit frequency was and vice versa. These are not as good as a duplexer but they do work very well. As an extra safety measure, I tend to add a band pass filter between this and the main Rx port to ensure the TX cannot see the Rx.
Leave a Reply