Hi Everyone- I'm looking for any thoughts or suggestions from anyone about some recent VSWR tests I've made on two antennas.
GAP TITAN BACKGROUND: I've had a GAP Titan vertical antenna running with my K2 (S/N 1599) for several years. The K2 and the GAP have served me very well (QRP WAS, 28 countries, etc.). The GAP is fed with about 80 ft of RG8U type coax (Belden 8214). Its VSWR measurements look completely normal to me when measured from here in my shack using an MFJ 259B meter. For example, typical VSWRs on 20m range from about 1.7 to 2.1 measured directly at the feedline PL259 connector. Most of the other seven GAP bands display similar "expected" VSWR ranges. Here in my shack the GAP feedline connector is attached to the center (common) port on a manual (not electronic) Delta-4 coaxial switch. The K2 and a couple of other rigs (Drake and Heathkit) are connected to the switchable Delta-4 ports. That arrangement enables simple rig switches to the GAP antenna without having to move the feedline from rig-to-rig. Measurements of feedline VSWR made THROUGH the Delta-4 switch to the GAP antenna with a 259B meter produce very similar results to those made directly at the feedline connector (i.e. with the switch bypassed). Conclusion: the Delta-4 switch seems completely transparent to the rig/feedline system. So far so good. HEXBEAM RECENT ADDITIONS: I recently put up a five-band HexBeam (2 wire-type elements for each of the five bands, 20m-10m). It seems to perform very well. The K2's KAT2 tuner likes it, as do the two other rigs and tuners I have (Drake and Heathkit). In the process of finishing the new Hex antenna, and "shaking down" its performance after installing it, I discovered one defective feedline PL259 connector which I replaced (naturally, outdoors on a windy day). Following that, I measured the HexBeam's VSWR across its five bands from the shack feedline connector with the 259B; all was well with it. VSWRs measured between 2.2 and 1.5 with no strangeness or instability seen on any of its five bands. Values on 20m, for example, ranged from 2.2 down to 1.7, depending on frequency. Similar measurements show up on the Hex's other four bands. (The top of 10m is somewhat higher, but that's not my issue.) MY ISSUE: Even though the HexBeam's 20m VSWR measurements appear quite normal made directly at its shack feedline connector using the 259B meter, they are VERY DIFFERENT when measured through a Delta-4 switch. The GAP antenna's VSWR's are very normal-looking when made through its Delta-4 switch, but the HexBeam and 259B meter are NOT HAPPY with a Delta-4 switch in place. (The HexBeam's Delta-4 switch is actually a separate switch, not the same one the GAP is connected to.) For example, instead of seeing a 20m range from 2.2 down to 1.7 on 20m WITHOUT the Delta-4 switch in place, I see values from about 4.5 or 5.0 across the whole band WITH IT IN PLACE. The 259B meter also appears quite "skittish" making measurements through the switch. It seems unable to decide on R,X and SWR values that remain reasonably stable. Something about the Delta-4 switch seems to have upset the HexBeam's VSWR applecart when being tested with the 259B. I see no such strangeness when measuring through the switch to a dummy load or to the GAP antenna when connected to the same switch. The only unexpected results seen through the switch are those made to the HexBeam. Just for jollies I decided yesterday to ignore the apparent problem, and just let my K2 and other rigs run on the HexBeam, each with its own tuner. All were happy, with the HexBeam's directivity quite obvious on all of them. I've disassembled both of my Delta-4 switches, cleaned their contacts, verified that all of my cable connections to the switches are secure and correct, and that no other dumb-thumbing factors have been introduced by me. I've done all the usual loosening-wiggling-tugging efforts to see if I can find a cable connector that might be in trouble, but nothing has shown up yet. MY QUESTION: Has anyone else ever used Delta-4 switches and seen similar unstable/unexpected VSWR results, either with a HexBeam or some other antenna connected to it? It seems obvious that the switch, only when connected between the HexBeam and a rig, introduces some sort of VSWR increase, but I've run out of ideas for what to try next. Yesterday my granddaughter said, "Just quit measuring and start QSOing!" Ah, the wisdom of a 12-year-old, huh? Thanks and 73 to all for the bandwidth and for any thoughts. Steve Banks K0PQ _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
