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#1
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Craig Buck wrote:
Read up on the topic of linear loading. You can bend that wire back on itself and increase the total length of wire. There are discussions of this in ON4UNs Low Band Dxing book. One commercial example is the Cobra Ultralite at http://www.k1jek.com/. I use a top center fed L. One side is horizontal and the other side is vertical. Fed at the top center with ladder line. Cebik has several articles on his site about center fed Ls. No ground plane, horizontal and vertical polarization, fewer nulls in the pattern. Very nice I think the center feds make a lot more sense for multiband operation. You're absolutely right, Craig... in principle. But Richard's situation reflects the reality for many British hams whose house is at one end of a short and narrow rear lot. With neighbors very close on all sides, we're lucky to have even one mast, so center-fed antennas are often not very practical for us - they either sag in the middle or wind up in a very sharp inverted-V configuration. As a result, we're very much forced towards considering end-fed or base-fed solutions. However, I wouldn't go near an end-fed long wire or zepp configuration, because of the very high risk of feeding the RF return currents into the mains. Been there, done that, had the doorbell ring! Living in that situation myself, my best solution has been a 30-33ft vertical at the far end of the garden, fed against the best ground system I can manage. This can be fed directly on 7MHz; with an ATU at the base it is good for 10, 14 and 18MHz, and is usable on the higher bands too. Over the years, this system has acquired an auto-ATU at the base, and has evolved into a guyed tilt-over mast with various quick-change "accessories" that can be attached at the top. A lightweight 12ft fishing pole makes a taller vertical, which has slowly crept up to 45ft; or a selection of horizontal loading wires running back towards the house at the 33ft level make inverted-L configurations for the lower bands. With the auto-ATU, any configuration can easily be loaded on any band. It won't be optimum on more than one HF band, but it will get you on the air on *every* band - and that's what counts for most. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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#2
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"Ian White, G3SEK" wrote in message ... But Richard's situation reflects the reality for many British hams whose house is at one end of a short and narrow rear lot. With neighbors very close on all sides, we're lucky to have even one mast, so center-fed antennas are often not very practical for us - they either sag in the middle or wind up in a very sharp inverted-V configuration. As a result, we're very much forced towards considering end-fed or base-fed solutions. Although center-fed is not totally impossible or out of the question, you are right, a lot of UK hams have small back lots/gardens and so many of us do tend to seek verticals or end-fed arrangements with the feed point away from the house. In my particular case, the problem with a vertical is that it would practically be surrounded on all sides by either trees or the house, so I'm not sure if going for a vertical alone would be a good idea, and that's why I'm considering either an inverted-L or zepp or something better. However, I wouldn't go near an end-fed long wire or zepp configuration, because of the very high risk of feeding the RF return currents into the mains. Been there, done that, had the doorbell ring! Noted. Living in that situation myself, my best solution has been a 30-33ft vertical at the far end of the garden, fed against the best ground system I can manage. This can be fed directly on 7MHz; with an ATU at the base it is good for 10, 14 and 18MHz, and is usable on the higher bands too. Yes. Any vertical at my QTH would be about 10 metres away from the house to the south, and about 2 metres away from tallish conifers to the north. A vertical would seem to be hemmed in to me. No clear take of in any direction actually. The problem with using a center-fed arrangement, is that the most I could put up in backgarden would be ap 40 metre doublet as per: x------------------- | \ | \ | \ | \ | \feedline back garden But the feed would be at the top of a 10 metre mast. I would have to have the feedline go in at an angle. So one thinks perhaps I need to end-feed as per: ------------------- | | | | | x back garden BUT, I could be daring and do this: / | \ / | \ / house \ back garden front garden Erect a 40 dipole, feeding at point of small mast on chimney stack of house. That means half of the antenna ends up in front garden. Or even put up cobra: http://www.k1jek.com/index.html Junior does not do 160 though. |
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#3
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"Richard" wrote in message ... So one thinks perhaps I need to end-feed as per: ------------------- | | | | | x back garden Latest thoughts: If I could get a decent ground (and that's unknown) I bet I could do a lot worse than an inverted -L, to use for 40, 80 and 160. Best I could do: 10m 10m ------------------------------------------------ | | | pole on house | 10m | | x feed back garden front garden Yep, might be worth a try if I can get a decent ground. |
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#4
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"Richard" wrote in message ... Best I could do: 10m 10m ------------------------------------------------ | | | pole on house | 10m | | x feed back garden front garden or even better perhaps: 10m 10m ------------------------x------------------------ | | feed | | pole on house | | 6m | 6m | | | | back garden front garden Getting G5RV-ish now. Not that great for 160 though. |
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