USB -serial converters can rise the local noise level by 3- 6dB. General eliminating digital originated noise is much more important then using a low noise pre-amp of course. A low noise pre-amp is made useless by this noise. If the USB-serial is just plugged in without any RFI protection it can spoil the noise floor on higher bands like 50MHz and others ( i did not test yet 70) But I noticed a serious noise increase when starting the logger program. Also a intermittent noise burst effect 1/ second can be noticed. This noise burst runs synchronised with the data string over the serial port. When starting N1MM CAT communication over the USB-serial the base noise clearly came up 3-6dB Then using the big toroid and a better shielded USB cable it was better. It is tricky this USB-serial chip noise because it will not stop immediate after closing the CAT communication. It will hang i...
Ham radio in JO33hg31 53.15N 6.35E