I have the DX Engineering preamp that I use with the DX Engineering portable flag and can confirm the 4.5 dB noise figure. Using the methods I described here in an earlier post, I measured the noise figure as between 4 to 5 dB.
Also I measured the gain (S21) from 0.1 to 30 MHz with my VNA-2180. It comes out to be 32 dB at 1.8 MHz. Overall the gain response is essentially the same as what WD8DSB measured on a prototype of the preamp and reported on his Web page (https://sites.google.com/site/portableflagantenna/). There is a broad dip in gain of about 1 dB in the middle of the HF range, but it's inconsequential. Finally I measured the input impedance (S11) of the DX Engineering preamp. It varies a bit with frequency but when reported as SWR relative to 50 ohms, it ranges between 1.2:1 and 1.5:1 over the HF range. It will be a fine match for the flag which has a 50 ohm feedpoint impedance. Overall I think these are very good numbers for a relatively inexpensive preamp that is portable and battery powered. (Disclaimer: I have no affiliation with or commercial interest in DX Engineering). 73, John W1FV -----Original Message----- From: Topband [mailto:topband-bounces+john.kaufmann=verizon....@contesting.com] On Behalf Of Don Kirk Sent: Tuesday, March 9, 2021 6:22 PM To: topband Subject: Re: Topband: Portable Flag follow up (DX Engineering preamp noise figure update) I should have said the so the 4.5 dB noise figure is certainly not unreasonable. Sorry for the typo. 73, Don (wd8dsb) On Tue, Mar 9, 2021 at 6:20 PM Don Kirk <wd8...@gmail.com> wrote: > A couple of weeks ago there were a lot of postings about my portable flag > for radio direction finding (for tracking down RFI), and someone asked > about the DX Engineering preamp that was designed for use with my portable > flag and specifically what the noise figure was for this preamp. Tim > (K3LR) said DX Engineering would measure it, and today he reported it > measured 4.5 dB. > > Tim mentioned that there were trade offs in the design such as low current > draw and high gain, so the 4.5 dB noise figure is certainly unreasonable. > It really is the only preamp I now use with my portable flag, and very > pleased with how it works. > > Just FYI, > Don (wd8dsb) > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector