Hello everyone!
Does anyone know if it is safe to connect 2 base scanner antennas to one radio? Also, is it safe to connect 2 scanners to 1 antenna?
Thank you
Depends what you want to achieve.
Co-phasing typically refers to two or more antenna elements operating on the same band. The aim is to obtain higher gain, by beam steering/concentration. Co-phasing relies on careful antenna spacing and tuned phasing lines (typically 75ohm coax for 50ohm antennas) to ensure correct phase & impedance matching back to a single 50ohm feed line. Because 'tuned' lengths of coax are used to join two 50ohm antennas to the feed line, co-phasing only works on a narrow band of frequencies (+-5% from the tuned frequency). Get things wrong and performance can be much worse than a single resonant antenna.
Multicoupling on the other hand, is a different kettle of fish.
This is where two or more antennas or radios on different bands are connected to a common feed line/coax. Each antenna/radio is isolated from the other antenna/radio by the use of High pass, Low Pass or Bandpass filters.
Multicoupling works very well and single or double stage LC High pass and Low pass filters are relatively easy to build and can be housed in a small IP66 die cast enclosure.
For example,
If you wanted an efficient 35Mhz antenna as well as good VHF Hi/UHF performance, it is relatively simple to build a 2 port diplexer/multicoupler with a 80Mhz cut off frequency. Then you can connect a resonant 35Mhz antenna (vertical dipole or similar) to the LPF port, a discone on the HPF port and a single low loss coax coming back into the shack. In the shack, you can either run the single coax into one scanner, or build another diplexer of exactly the same design, to split the 35Mhz signals to one scanner and the VHF hi & UHF signals to another scanner. Either way, it gives good performance with relatively low loss (the diplexers should only introduce ~1dB of loss each, which is barely noticeable).
I should also point out that running two scanners from a single coax using a simple coax 'T' connector can be problematic. It will work OK for stronger signals but you will see at least 3-6dB signal reduction on all signals/bands and much greater attenuation on some signals. In addition, since there is no isolation between the scanners, any noise or interference generated by one scanner will degrade reception on the other. Ideally, you should run a dedicated 50ohm power splitter/combiner, which will provide 20-30dB isolation from one scanner to the other and will prevent any interaction.
