Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old September 9th 04, 08:38 AM
Ian White, G3SEK
 
Posts: n/a
Default

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
  #2   Report Post  
Old September 9th 04, 10:07 AM
Richard
 
Posts: n/a
Default


"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.

  #3   Report Post  
Old September 9th 04, 11:04 AM
Richard
 
Posts: n/a
Default


"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.

  #4   Report Post  
Old September 11th 04, 10:16 PM
Richard
 
Posts: n/a
Default


"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.

Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
ladder line construction methods? Larry Gagnon Antenna 75 July 5th 20 07:31 PM
ladder line recommendations? Larry Gagnon Antenna 8 June 17th 04 07:14 AM
Ladder line question ???? Bob Antenna 2 April 24th 04 05:54 AM
Ladder Line or Coax For Reception only? Walter Antenna 12 October 11th 03 04:16 AM
Complex line Z0: A numerical example Roy Lewallen Antenna 11 September 13th 03 02:04 AM


All times are GMT +1. The time now is 05:56 PM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017