TDK Data Sheet<\/a> for Sl ceramic capacitors.<\/p>\nFor the 10m trap a value of 10pf was used, with 16 turns of 18ga stranded wire tightly wound on a 1 inch diameter piece of fiberglass tube.\u00a0 (calculated inductance is about 3.25uh)\u00a0 This originally resonated about 27500, but crept up after taping and sealing to 28000.\u00a0 Decided to roll with them as constructed.\u00a0 These may be fragile, too fragile for portable use, as 18ga wire was also used for the connections.\u00a0 NOTE: USE LARGER GA WIRE FOR CONNECTIONS.<\/p>\n
The “tricksey” part discovered previously is that using caps with a large enough reactance on the upper band helps them survive by limiting the current actually flowing through the capacitor.\u00a0 At the 100w levels the voltages are less of an issue than the current handling.\u00a0 Using parallel-series combinations can also help, depending on what value caps are available.<\/p>\n
The downside is that the inductance value to resonate the trap for 10m becomes relatively large.\u00a0 This makes tuning the antenna for the 15m band “tricksey”.\u00a0 The 15m tail is short, maybe 15 inches from the relatively large inductance used in the trap.\u00a0 When trimming, very small trimmings move the 15m resonance quite a bit more than on a normal 15m dipole.\u00a0 The good news is that the 10m band is only very slightly effected by trimming wire on the 15m side of the trap.\u00a0 The 15m tails needed to be replaced and re-trimmed after trimming a 2 inch bit of wire moved resonance from 20.85mhz to 21.65mhz.\u00a0 oops.\u00a0\u00a0\u00a0 SMALL SNIPS FOR 15m tuning!!!!<\/p>\n
After trimming, the 10m\/15m antenna is good from 28000 to 28750, and also covers the entire 15m band.\u00a0 STOP….DO NOT TRIM AGAIN!<\/p>\n
The 20m\/40m version is built with a trap resonance at 13.65mhz.\u00a0 The 20m legs are approximately 15ft long.\u00a0 The 40m legs will be about the same.\u00a0 (?actual measurements?)\u00a0 Total antenna length of about 60 feet.<\/p>\n
Both of the 2019 home 20m\/40m trap dipoles can be easily matched with the Kenwood TS-590 internal tuner for use on 10m as well, which provides options.\u00a0 Worked JA’s on 10m using the 20m\/40m trap dipole several times now. The new version for the 20m\/40m\u00a0 portable does NOT tune on 10m, probably because of the different value of capacitance\/inductance used, or maybe because the new antenna traps resonate at 13.65Mhz instead of 12.5Mhz.\u00a0 The new trapped antenna covers the entire 20m band, with the highest SWR of 1.5:1 at 14000-14015.\u00a0 The 40m band is below 1.5:1 SWR from 7000 to about 7250, with the swr going to about 2.3:1 at 7300.<\/p>\n
(For future testing, add turns<\/p>\n
Using the new 1 inch o.d.(~25mm) fiberglass form material as the coil form and the TDK capacitors:
\nFreq\u2014\u2014\u2014Capacitor——-\u2013# turns calculated\u2014\u2014#turns actual\u2014\u2014-
\n27.7Mhz\u2014>10pf————->12 turns (approx)\u2014\u2013> 12 turns, 28Mhz(use 12.5?) (calculated inductance of 3.25uH as constructed)
\n20.66Mhz\u2013> ?????
\n13.75Mhz\u2014>\u00a0 34pf————>16 turns —— \u2014\u2014\u2013> 16.5 turns, 13.65Mhz\u00a0 (calculated inductance 4.04uh)
\n6.75Mhz\u2014-> 16.33 turns<\/p>\n","protected":false},"excerpt":{"rendered":"
After a detour to building the 2 band trap dipoles using rg-316 type coax, the worm turned. The failure of a couple of the coax trap antennas due to incomplete sealing and weather proofing the coax became a problem. The antenna at home failed. Two of them. Then the antenna being used for portable ops failed during the 2024 NC QSO party. In the meantime, the home antennas built from coils and capacitors for 40m\/20m are still in use 4 years later with no change in resonance points.<\/p>\n
Rather than continue with a seemingly fragile system it was time to revert to the coil-and-cap design. Avoiding the cap failures previously experienced on the 10m\/15m antenna is addressed by using caps with low enough values to be appropriate for the 10\/15 version. So a supply of the TDK ceramic caps was laid in. These caps have 3KV and 6KV ratings. Parts#810-CC45SL3JD080DYGN (example is 8pf SL 6kv) from mouser. TDK Data Sheet for Sl ceramic capacitors.<\/p>\n
For the 10m trap a value of 10pf was used, with 16 turns of 18ga stranded wire tightly wound on a 1 inch diameter piece of fiberglass tube. (calculated inductance is about 3.25uh) This originally resonated about 27500, but crept up after taping and sealing to 28000. Decided to roll with them as constructed. These may be fragile, too fragile for portable use, as 18ga wire was also used for the connections. NOTE: USE LARGER GA WIRE FOR CONNECTIONS.<\/p>\n
The “tricksey” part discovered previously is that […]<\/p>\n
Continue reading Going Full Circle – Trap Dipoles Ageeeeeeen.Ageeeeeeen.Ageeeeeeen….Part 4<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[7,10,61],"tags":[],"_links":{"self":[{"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=\/wp\/v2\/posts\/3798"}],"collection":[{"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3798"}],"version-history":[{"count":9,"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=\/wp\/v2\/posts\/3798\/revisions"}],"predecessor-version":[{"id":3848,"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=\/wp\/v2\/posts\/3798\/revisions\/3848"}],"wp:attachment":[{"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3798"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3798"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/w4kaz.com\/qth\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3798"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}