[Elecraft] KAT-500 and 30' Flag Pole Antenna Users?

[Javier Campos]

Thanks to all for the replies. Excellent points and real life experiences have provided some valuable insight.

The antenna should be her in about a week or so.  

I will use my MFJ antenna analyzer (I hope it still works) after I get it standing up and eventually (need to let the "look" set in of just the aluminum) for the neighbors before I attach the UNUN and the radials. 

After all, it's a "Flag Pole" to my HOA so I just need to let it sit there and let the novelty wear off before I attach UNUN, lay the radials and dig  the trench for the coax.

It will also give me time to freshen on on plotting the R+jx on the smith charts, again after 24+ years from doing in it in college.

Thanks again and you will all here from me once this is all installed and put together and on the air.

Javier NM6E/5 


________________________________
 From: John Fritze <fritzejohn at gmail.com>
To: elecraft at mailman.qth.net 
Sent: Sunday, July 28, 2013 2:35 PM
Subject: Re: [Elecraft] KAT-500 and 30' Flag Pole Antenna Users?
 

Javier,

Here's some additional info for you to my first post.

A lot of great info can be found here regarding the antenna design you are
considering:

http://www.sgcworld.com/technicalInfoPage.html

If the tuner is at the radio and the output from the tuner is coax (such as
a built in tuner in the K3) the tuner is tuning the coax and not the
antenna.  It will make the rig happy and isn't that what we mostly are
looking for anyway?  But the main problem is how do we get the most
transfer of power between the coax and the antenna?

A schematic circuit of any antenna is a resister, inductor and capacitor in
series.  By adjusting the capacitance or the inductance we can try to
arrive at 50 Ohms to match to coax.  That's what a remote tuner is trying
to do by adding capacitors and coils into the circuit.  Once the match is
found, then the rig output, coax, and antenna are all 50 ohms giving us the
maximum transfer of power so it is not burnt up as heat in the coax.

A remote tuner tunes the antenna and the coax is effectively flat SWR from
the rig to the tuner.  One problem I have found is that coax should NEVER
be used at the output of a remote tuner (BUT we all do it don't we, even I
do on occasion)!   From the remote tuner to the antenna it is all antenna
and it is all radiating.  West Marine sells a product called high voltage
wire, it is 10 or 12 gauge, stranded and tinned, covered with a white PVC.
It is not cheap but it is a really good product.  Sometimes a remote tuner
will tune with a short coax at the output, but it won't be happy and you
will find that the tuner will hunt for a solution.

One other issue folks sometimes have is trying to tune the vertical when it
is too short for the tuner.  Ideally you need to be 42-43 feet to work
80-10 meters.  If you want to sometimes get on 160, then you need to be
closer to 55 feet at a minimum, but then you are compromised at 10-6
meters.  Not because the antenna won't tune the longer vertical but because
angle of take off is too high. If you try to tune an antenna which is too
short, the voltages at the relays can be very high, causing arching and
burning of relay contacts.  One way around this is to tune at a very low
output, then raise power once the relays have set where they need to be.
Be careful to not vary too far in frequency however!  Another solution is
to add in inductance by jumpering in a coil when you want to work the lower
bands.  There are numerous articles in QST about getting a 42 foot vertical
onto 160 meters.

Remember: a properly grounded vertical antenna is only about 25-30 ohms.
So right off the bat you have a 2:1 mismatch. I also do not use an UNUN or
balun of any type and have not had any issues.  Again, you need a VERY GOOD
GROUND.

I know for the real antenna gurus out there everything I have stated is
kind of simplistic and there are tons of variables and best solutions per
application.  I am just giving you 30 years of real world experience.


-- 
John Fritze Jr
K2QY
AARA president 2013
ACACES secretary 2013
Albany County RACES Radio Officer
ARES ENY DEC Northern District
Hudson Div. Asst. Director
Twitter: @k2qy
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