HI Steve, Thanks for the nice implementation comment.
The portable flag front to back ratio is highly related to the elevation angle and frequency of operation (just like any terminated loop), and therefore I did not want to overstate the front to back ratio in my portable flag article. I designed the portable flag for direction finding local RFI (ground wave based signals) and therefore made sure I selected an appropriate termination resistor to provide a very deep null at low elevation angles on 160, 80 and 40 meters where I often deal with RFI (the portable flag has a very high front to back ratio at low elevation angles), and because of this it also has exceptional front to back ratio at low elevation angles down in the AM Broadcast Band. Very small flags have just as good front to back ratio and RDF as a full size flag as long as the appropriate termination resistor is used. The problem is when the flag becomes too large for the frequency of operation which causes the directional properties to degrade. You can see some front to back ratio vs. elevation plots for my portable flag on my simple portable flag website and here is the URL to that site: https://sites.google.com/site/portableflagantenna/home Problem with very small flags is that the noise figure of the preamp becomes a critical parameter, and because of this I don't recommend attenuators be placed before the preamp as this causes degradation in the signal to noise ratio. I stumbled upon this issue when doing field tests on one of the DX Engineering prototype preamps, and had them change the design so the attenuators now come after the actual amplifier stage which solved the problem. Everything I said above about the performance of very small terminated loops assumes no interaction with surrounding objects, and ignores issues related with feedlines since the feedline is very short on the portable flag. P.S. I make no money from DX Engineering as I agreed to not be paid in order to keep the price of the portable flag as low as possible. 73, Don (wd8dsb) _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
