Further to Wellbrook ALA1530LN connection to HI-Z port
Posted: Mon Apr 23, 2018 9:29 pm
If I understand the following correctly, it should be possible to connect the ALA1530 interface output directly to the Hi-Z port without modification, or can someone tell me whether I am mistaken?
Ports A and B are intended as general purpose RF ports, but the Hi-Z port is really intended as the
prime port for HF and below and has been optimised as such. This is one of the major changes in
thinking from the RSP1. The reasoning here is that you seldom get a single antenna that gives
optimised performance from VLF to UHF, and so the majority of people will tend to use separate
antennas for HF and VHF/UHF. We chose a 1 K ohm impedance for this port, to simplify the
connection to a random wire antenna which is the antenna of choice for HF for many of our
customers and is also a good choice for frequencies below 1 MHz. Because of the long
wavelengths involved at HF, this port also works well for 50 ohm antennas as long as the feed
cable is not excessively long, but for long feed cables, you can simply use a reverse 9:1 balun
between the Hi-Z input and the end of the feed cable to achieve an adequate match to 50 ohms
for this purpose. When operating below 1 MHz (down to VLF), though, the direct connection will
work best, even with a 50 ohm feed as the high impedance termination will deliver the highest
terminal voltage at the input to the RSP2 and reflections will really not be a problem because the
wavelength is so long
Ports A and B are intended as general purpose RF ports, but the Hi-Z port is really intended as the
prime port for HF and below and has been optimised as such. This is one of the major changes in
thinking from the RSP1. The reasoning here is that you seldom get a single antenna that gives
optimised performance from VLF to UHF, and so the majority of people will tend to use separate
antennas for HF and VHF/UHF. We chose a 1 K ohm impedance for this port, to simplify the
connection to a random wire antenna which is the antenna of choice for HF for many of our
customers and is also a good choice for frequencies below 1 MHz. Because of the long
wavelengths involved at HF, this port also works well for 50 ohm antennas as long as the feed
cable is not excessively long, but for long feed cables, you can simply use a reverse 9:1 balun
between the Hi-Z input and the end of the feed cable to achieve an adequate match to 50 ohms
for this purpose. When operating below 1 MHz (down to VLF), though, the direct connection will
work best, even with a 50 ohm feed as the high impedance termination will deliver the highest
terminal voltage at the input to the RSP2 and reflections will really not be a problem because the
wavelength is so long