Topband: Hairpin Matching Coil Questions
To amplify a little on some other comments - For an Inv L, and a decent radial system, with a coil shorted across (shunt) the vertical wire input to the braid/radials, the otherwise low impedance can be transformed to 50 ohms. One way to do it is to use an antenna analyzer to measure the unmatched impedance and then adjust the length of the horizonal-ish leg to get the reactive component to be roughly -20 ohms (capacitive, and the resonance with be ~ 1.9 MHz for a 1.825 target) and the resistive component well less than 50. Using the measured resistive component (which changes slowly with frequency) you can find what reactance you really need in the unmatched antenna for a perfect hairpin match with available calculators or from that Hairpin matching article in Jun QST. Once the length is fine adjusted to get the needed reactance, the needed coil impedance (and inductance) can then be calculated or found from a graph. Then wind your coil long and find the tap (or stretch) that minimizes SWR at your favorite frequency. A bit more back and forth may be required. No need for beauty and the coil is not huge. From multiple personal experiences, this can certainly be done, although beware that a NEC model to get initial antenna dimensions may be far enough from reality (dimensions way too long in one case and long in others). This may be particularly painful if no antenna analyzer is available. Some experiences recounted on my webpage and a calculator is there. Bill N6MW _ Topband Reflector
Topband: THE ITINERANT 160 METER ANTENNA PROJECT - Follow Up
My previous request for suggestions for a relatively simple/transportable TB ant got some responses that have been incorporated into a design and construction that might be useful to others. It is a dual band 160/80 trapped vertical/T with two load top wires and two elevated gull wing radials using the spiderbeam 60' mast. It is relatively compact and works respectably on 160 and perhaps somewhat better on 80. Highlights are only 55' of the mast is useful (bending), radials are 75' (tuned to 80) and ~ 17' high, the 2 top load wires are 60' (tuned to 160), trap is coax type (Low-Z wired), a single hairpin match shunt coil setting allows no-tuner 160/80 use without any switching with limited BW and use on 160 requires a GOOD common-mode choke (this is a rather OCF antenna on 160). The hairpin matching requires patient trimming of wire lengths so if you are willing to complicate things a bit, a capacitor could be tossed in for an L-match. It is also very likely that putting this antenna up at another location would force a revisit to the tuning issues. As always YMMV. See http://n6mw.ehpes.com for details - at the end of the antenna project list. Bill, N6MW _ Topband Reflector
Topband: ITINERANT 160 M ANTENNA - Response Summary
So gently getting back to the topic of the original post which was: Getting thoughts on relatively simple and relatively inexpensive portable 160 m antenna, potentially deployable by one person, that allows for flexibility and somewhat predictable tuning for use on modest Dxpeds or rare location indigenous ops. Strawman proposal was for Inv L 50’(or more) alum mast with elevated radials all tuned with “hairpin” shunt coil – plus a request for suggestions and potential actual physical assistance with testing/assembly/distribution. Principal thoughts to date by TB types posted and direct: 1. More top wires than just one – doable with minimum additions provided the site has space. Should improve performance somewhat, requires top wire supports in other directions (which may only be a minor issue) and some more wire. 2. Mast higher than 50’ - I believe at 55’ (~17 m) it is still quite possible to hoist it up (maybe not walk up but a rope attached 1/3+ of the way up) 3. Use 18 m fiberglass telescope instead of alum. - Doable and can be walked up they say, but nearly twice as heavy as alum, more expensive and bending at top reduces effective height a bit. But still if you’ve got one . . . 4. Ground radials instead of elevated. - Could be good for some locations but requires 20+ m radius circle thick with wires. The innkeeper might not be pleased and also space may not be available unless you go the tent/generator route. I suppose the antenna product could be in two flavors, ground and elevated, with possible different tuning of the top wire. 5. Go to a site that has nicely spaced high palm trees (on the good propagation side of course) and then . . . - I welcome volunteer advanced palm tree scouts. Yet perhaps not all (or even most) interesting 160 m entities have palm trees. - Yet the point is well taken that a good site with advanced planning (Google Earth/eyeballs) is important (when possible). This matter has been looked at for KH8 but I am looking at broader uses as well. 6. Matching not worth the effort with modern ATUs - Yes but I would not think of trying a semi-serious 160 m effort with low power (or difficult to match antenna), and the high power matching units have $, size and weight issues. The current plan has the charm of a simple, flexible matching coil even at the expense of tuning by fiddling with top wire and/or elevated radial lengths 7. Receive antenna use - I purposely did not mention this just to see if it would be seen as an oversight among TBers. My only personal experience is I don’t have one and there have been a significant number of high end 160 stations (who surely have Rx ants) I could hear but could not hear me (my ant is a bit better than the one proposed here and with 500 w). Of course, his story may not hold up for a rare-ish DX station. Anything else? Bill N6MW ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: THE ITINERANT 160 METER ANTENNA PROJECT
The plan is to develop a simple, relatively inexpensive, relatively light weight and shippable/airline transportable 160 antenna kit for one man quick deployment for modest DXpeditions or contributed for use by resident hams in rare-ish (for 160 m) locations.The ability to make adjustments to actual deployments to provide matching is important since such antennas are famously variable due to soil and local obstruction environment and there should not be a need for antenna matching hardware, especially at the planned higher powers. First cut electrical design:Inverted L using telescoping aluminum tubes, two elevated radials and hairpin matching. Mechanical features of a prototype that was deployed: 9 Alum tubes 6', .058 walls, 2 diameter through 1 diameter -- this gives a 50' or 15.3 m mast (it can be pulled upright by 1 person, or probably telescoped up also) #14 wire ~ 28 m for top wire and 2X ~34 m radials (values after some adjustment, not unique, some tradeoff between the top and radials) Base - 2 thicknesses of Walmart (cheap 8X11) ¼ plastic cutting board resting on ground with a ~ 1.5 wood cylinder bolted in the center.SO-239 connector screwed to the board. Guys -- 4X 3/32 dacron rope attached at 7 tube height, angled at ~ 45deg Guys held down by sandbags (very effective and moveable) Inv L top wire end was at ~ 2.5 m height with a support of opportunity (e.g., a tree) ~ 25 m from base Radials have their closest support near the base from plastic rings looped through each of an opposite pair of the guys at ~ 6 m high and 6 m from the mast.The radials therefore go from the base to the rings at about a 45 degree angle.(Elevating the base and everything else, by a meter did not seem to affect the impedance.Beyond that, supports of opportunity were used - above neck height is always nice. This produces, with some fiddling with wire lengths, an impedance around 20 -- j20 which can be matched using a practical hairpin coil shunt of inductive reactance ~ 45 ohms ( 4 microHenrys, say 5 turns 4 dia). More details of the test case including the EZNEC example are shown on my website.There are obviously a number of ways this design could be modified/improved, several discussed on the website.However, the tradeoffs with size, weight and complexity must be considered in the light of the mission here which includes transportability and ease of deployment. I am looking for collaborators to contribute ideas to help improve, and potentially, test design issues.Check out the website at http://n6mw.ehpes.com http://n6mw.ehpes.com/ for the Itinerant 160 m antenna project expanded discussion toward the bottom. The immediate target is designing and assembling a respectable 160 m antenna that might go to KH8 on a DXpedition. Bill, N6MW billsstuff(at)gotsky.com ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: ITINERANT 160 M ANTENNA PROJECT
The plan is to develop a simple, relatively inexpensive, relatively light weight and shippable/airline transportable 160 antenna kit for one man quick deployment for modest DXpeditions or contributed for use by resident hams in rare-ish (for 160 m) locations. The ability to make adjustments to actual deployments to provide matching is important since such antennas are famously variable due to soil and local obstruction environment and there should not be a need for antenna matching hardware, especially at the planned higher powers. First cut electrical design: Inverted L using telescoping aluminum tubes, two elevated radials and “hairpin” matching. Mechanical features of a prototype that was deployed: 9 Alum tubes 6’, .058” walls, 2” diameter through 1” diameter – this gives a 50’ or 15.3 m mast (it can be pulled upright by 1 person, or probably telescoped up also) #14 wire ~ 28 m for top wire and 2X ~34 m radials (values after some adjustment, not unique, some tradeoff between the top and radials) Base - 2 thicknesses of Walmart (cheap 8X11”) ¼” plastic cutting board resting on ground with a ~ 1.5” wood cylinder bolted in the center. SO-239 connector screwed to the board. Guys – 4X 3/32” dacron rope attached at 7 tube height, angled at ~ 45deg Guys held down by sandbags (very effective and moveable) Inv L top wire end was at ~ 2.5 m height with a support of opportunity (e.g., a tree) ~ 25 m from base Radials have their closest support near the base from plastic rings looped through each of an opposite pair of the guys at ~ 6 m high and 6 m from the mast. The radials therefore go from the base to the rings at about a 45 degree angle. (Elevating the base and everything else, by a meter did not seem to affect the impedance. Beyond that, supports of opportunity were used - above neck height is always nice. This produces, with some fiddling with wire lengths, an impedance around 20 – j20 which can be matched using a practical “hairpin” coil shunt of inductive reactance ~ 45 ohms ( 4 microHenrys, say 5 turns 4” dia). More details of the test case including the EZNEC example are shown on my website. There are obviously a number of ways this design could be modified/improved, several discussed on the website. However, the tradeoffs with size, weight and complexity must be considered in the light of the mission here which includes transportability and ease of deployment. I am looking for collaborators to contribute ideas to help improve, and potentially, test design issues. Check out the website at http://n6mw.ehpes.com for the Itinerant 160 m antenna project expanded discussion toward the bottom. The immediate target is designing and assembling a respectable 160 m antenna that might go to KH8 on a DXpedition. Bill, N6MW billsstuff(at)gotsky.com ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
