On Fri, Jul 15, 2016 at 4:21 PM, Jim Brown <j...@audiosystemsgroup.com> wrote: > Also, several changes of a dB or two add up.
Oh Yeah. Particularly on any band where it's common to have poor but open paths. Oh Yeah. Sing it again, Sam.... These last few dB's count on 160 particularly, just about all the time, on 80 an awful lot of the time. These are bands where even a merely moderate loss can put you in the noise at the other end. The real expenditure of resources needs to be with the grey matter. As one evil friend persists in saying regardless of who it offends, "Don't-do-dumb-sh*t doesn't cost any money". RF loss is mostly self-inflicted. Maybe because looking at model patterns, we think we can get that predicted gain just by throwing up some wires in the same shape. But the model is missing the implementation and the environment. We have proven cases of self-inflicted 12 dB total losses to an antenna system. You *can* buy an amp to cancel out the 12 dB, that would be the same as 100 watts after fixing the 12 dB. Yeah, *measured* that one. That bad surely *is* uncommon. But would you take total 6 or 7 dB loss eliminated? That happens a fair amount. My evil friend also says "Fix stupid before spending money". He must have laughed for 15 minutes when I told him the 12 dB story. He could barely breathe. Of course that's really no fun if it was you or I that just did stupid, and my evil friend says "Fix stupid before spending money". Grrrr. But loss is loss. In some professions it's "First, do no harm." In antenna system design and implementation it's "First, do no loss." There are some exceptions. Distance to antennas and cost/suitability of feedline is a balancing act. Just do your best. At least try to quantify it, and mull on it for a while. Read up. Talk to someone who is not inside your own brain. We all have our personal blind spots, and good friends who will tell us the truth are priceless. Just one example, one local ham (not the evil friend) put up ON4UN style 4 x 1/8 wave raised radial systems for his phased pair of 160m verticals using #14 THHN. He did not strip the insulation. UV destroyed the insulation in only two years which had deteriorated to a rather strange appearance, but "something" was left of the insulation still hanging on the #14. The *measured* effective series resistance of the two radial systems was 18 and 21 ohms. The radials were replaced with BARE #12. After that the *measured* effective series resistance of the two radial systems was 4 and 5 ohms respectively. The R component of the repaired system feed of the vertical with the 5 ohm radials was now 38 ohms. Calculating backward, the 16 ohms of unnecessary deteriorated insulation series resistance would have produced a feed R of 54 ohms and a completely amazing 1.5 dB loss caused by the THHN insulation on the four 1/8 wave elevated radial wires. We don't know whether the THHN was that lossy from the get-go, as this parameter was not measured right after the THHN initially went up. It could have gotten better with the deterioration. We will never know. The local ham bought the THHN from his local home improvement store, just like me and the rest of us, for the reduced bulk cost, which is typically half the cost of the same length of bare wire from outlets who will actually sell you spools of bare #12. Said local ham is witness to a stripping technique I used that will allow you to strip the wire with a dull pocket knife at walking speed. Back to my evil friend, who says "Fix stupid before......" Grrr.... I will say positively that stripping THHN to create bare copper will eliminate certain losses. One really should consider it. My evil friend says "Leaving THHN insulation on wire used in antenna systems is stupid." Go shoot HIM. You should see his list of "stupids". Grrr, Grrr, and triple Grrr. It's hardly just leaving the insulation on THHN used for antenna wire. K9YC (not the evil friend) says "Also, several changes of a dB or two add up." And he surely is right, especially on the low bands. They do add up. Death by a thousand paper cuts. Used to hear a thing on TV a lot, "Do you know where your children are?" Remember that? Do you know where your losses are? Be just as irritated about a 2 dB loss out in the feed and antenna systems as you would be if your supposedly 1500 watt brick-on-key super-pileup-stomper amp, for which you just spent multi-kilo-bucks, would only load up to 950 watts, no matter the drive power. Oh yeah, 2 dB loss in an antenna system used for QRP? On any given day that can be the difference between weak-but-heard and no contact. The low band contesting season is just a few short months away, and approaching at the same speed as Christmas and New Year's. Go eliminate a loss or two. 73, Guy K2AV. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
