Re: Topband: Inverted L with elevated radials for topband

[Jeff Blaine <KeepWalking188@ac0c.com>]

When it comes to elevated radials, the amount of guys who have strong 
opinions on the subject are many - and unfortunately the amount of 
objective data behind those strong opinions is generally not existent.  
On the other hand, the N6LF work is one of the few well documented 
objective works available.
You won't go wrong drawing your radial design based on the N6LF graphs.  
As far as the performance and feedpoint question goes, build the best 
ground you can and then cook up the match network based on the measured 
values.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 3/5/20 5:43 PM, Grant Saviers wrote:
> comments in line
>
> On 3/5/2020 10:02, Gabriel - EA6VQ via Topband wrote:
> > I have some doubts about installing and inverted L with elevated 
> > radials for
> > 160m.  I have been searching in Google and find some contradictory
> > information, so I would appreciate very much if you can help me with 
> > your
> > own experience.
> As noted by others, N6LF has a wealth of modeled and measured data on 
> elevated radials.    antennasbyn6lf.com
> > The antenna would be supported by a 16 m (52.5 ft) high fiberglass pole
> > placed on top of a 3m (10 ft) high small tower with the horizontal 
> > part of
> > the L slopping down to a 5 m (16 ft) high mast about 23 m (75 ft) 
> > away.  Two
> > to four tuned elevated radials can be placed, although they will have 
> > to be
> > bent due to space restrictions.
> By "tuned" do you mean resonant 130ft +/-?  Again N6LF has data for 2 
> to 16 elevated radials, and with more they can be shorter.
> Also see his paper in Antenna Compendium 8 re inductively loading for 
> shorter radials.  I had only 2 75ft radials on a 52' mast.
> > Now the doubts:
> >
> >
> > What impedance can I expect at the feed point with this configuration?
> Having the radials as high as possible will minimize ground losses and 
> decease Z.  With 2x at 10ft plan on 25 to 30 ohms.
> > How to match it in order to feed it with a 50 ohm cable?  Some pages say
> > that no match is required, only a choke. Other pages say a hairpin is
> > necessary as the impedance can be too low. So other say that a tuner 
> > at the
> > base is required?    I am confused L
> SWR losses on 160 are so low that a 2:1 doesn't cost many db's. Too 
> keep your amplifier happier I use a 50::25 ohm transmission line 
> transformer.  make it or buy it.
> A good choke is a must.  Make the K9YC 4" #31 choke.
>
> > What performance for DX can be achieved by this antenna?  Is it 
> > really good
> > or do you have some better suggestion for a really small lot where no 
> > ground
> > radials are possible?
> You won't do better with anything else.  More radials will improve it 
> slightly.
> > Would it be worth to use a higher fiberglass pole, let's say 4 m (13 ft)
> > higher, in order to lengthen the vertical section of the L? Would the
> > difference be noticeable?
> The taller the better but probably less than 1 db gain.
>
> > Anyone has real experience setting up this antenna with elevated 
> > radials?
> > Most information I can find on Internet is related to ground mounted
> > antennas.
> Read all of what Rudy N6LF says, and you will be an expert.
>
> Grant KZ1W
>
>
> > Thanks in advance!
> >
> >
> > 73. Gabriel - EA6VQ
> >
> >
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