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Author Topic: Setting Up an internal antenna for IC-7000 50M side  (Read 597 times)
KD0JXP
Member

Posts: 4




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« on: January 09, 2013, 01:42:58 PM »

Hi all:

I have been researching my antenna choices for my Icom IC-7000 Rig for the 50M side.  I am highly restricted in what I can do antenna wise by our landlords and the fact that we live in the second floor of a three floor apartment building.  To give you an idea of the restrictions imposed on all tenants, this clause in our rules sums it up:  "The balconies will be kept free of all items, including bicycles and plants."  They allow satellite dishes apparently though, but an amateur radio antenna is just unsightly ;-)

I thought about running a loop around the balcony under the rim, but that will not give a very good yield as the loop would be small and I am trying to cover a few bands with the loop.  Therefore, I have decided to go with a loop around our living room ceiling and I have not taken measurements yet, but I am looking for some advice on wire to use, baluns, etc.

It looks like a 4:1 balun would be a good bet for the balun... the questions I have on the antenna are as follows:  As I stated, I have an IC-7000 rig and my autotuner is an LDG IT-100.  I have a coax cable that is 6' long (currently connected to a dummy load) and a 1 foot long from the radio to the autotuner.

I am questioning whether or not to run ladder line from a balun (the afore mentioned 4:1) to my loop which is going to be made out of what kind of wire (I do not yet know -- this is where help is welcome).  Or just run the loop from either side of the balun.

Hope this question makes sense and that someone can offer expertise.

Thanks,

Mike
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W5WSS
Member

Posts: 1597




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« Reply #1 on: January 09, 2013, 05:25:49 PM »

A 25ft X 12-15ft ish" horizontally oriented horizontally radiating rectangle worked reasonably well for me along with a wide range T-match tuner as a multiband antenna.
Consider a dipole as good if not better for this application as the pattern is roundish when low to the ground the difference in performance offsets the cost of twice the wire of a comparable loop.

 A circle shape may be best for omnidirectional service on the higher bands where the antenna approaches a 1/2 wave of height. Horizontal antennas including the horizontal loop when at low height above the ground greatly reduces  longrange dx contacts(there are exceptions but far and few between) mine was only 18' up so most manifested power was at high angles...I struggled to hear dx with it on 20M during the bottom of this past cycle although I worked allot during it's peak. During This cycle I have not seen those successes and have been limited by comparison vs the same antenna.

Mine was indeed inside mounted on the ceiling.

I fed it with 300 ohm line balanced twinlead. The line length was very short about 6' directly up to the loop. (the taught length that went from desktop to antenna) One could twist the line from top to bottom if needed.

Route the line straight and stood off the wall about 3" or the sheetrock will shear the transfer of power from rig to antenna and from antenna to rig.

A Tuner that integrates a balun is a shortcut for design to build around if not then:

See Dx Engineering for a tech talk on which outboard balun selection is best because it depends on where one operates the loop relative to resonance, there are basically three situations to think about.

73
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K0ZN
Member

Posts: 1525




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« Reply #2 on: January 10, 2013, 03:30:37 PM »

Hi...  Not trying to be difficult, but I don't understand what you mean by "50 m side".
50 meters is not an Amateur band??  What is the total length of your proposed loop?
Small loops have an extremely low radiation resistance and are very difficult to match efficiently in a transmitting application. Some sort of balanced antenna, even if bent around may be easier to match. Any way you can run a very small gauge wire of some reasonable length?

Respectfully, spending some time studying the ARRL Antenna Book would be a great investment and likely expose you to antenna options you are not aware of.

73,  K0ZN
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KD0JXP
Member

Posts: 4




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« Reply #3 on: January 10, 2013, 03:57:00 PM »

Thanks for the replies.

The 50 m side is the HF/50 Mhz side of the IC 7000 or not the 2M/220 connector ;-)

I have not figured out the length of the loop yet... while the ARRL Antenna book might be quite helpful, I am out of funds for the hobby for a while because I just bought both my HT and my IC-7000.  The Antenna Autotuner is additional to that and unfortunately just found myself unemployed (due to contract ending).  So it will be awhile before I can invest further than $50 into the antenna project.  The rub is that the balun I am considering runs $80, so I may be on hold indefinitely on this project, but it does not keep me from doing my research on it (although it is limited to sources that will not cost any money).

I do appreciate any help on this.  I need to make a loop that will encompass all the HF frequencies (if possible) and the real question is what gauge wire should the loop be.  I already am considering the 4:1 Balun and ladder line to the balun from the loop.

Thanks again,

Mike
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WB6BYU
Member

Posts: 12980




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« Reply #4 on: January 10, 2013, 04:48:03 PM »

There are lots of things you can do to get on the air for cheap, even if they
aren't "professional" quality.

Just about any sort of wire will do for an antenna.  I'd avoid iron or steel
wire if you have other options, and you have to be careful with aluminum
that the contacts don't corrode.  I used a lot of telephone wire for antennas
as a teenager because I salvaged a chunk of 22-pair cable from a house
under construction:  that gave me 44 wires each 4' long that I could hook
up in series.  My first ham antenna used Army field wire, and I currently have
an antenna up using aluminum electric fence wire.  My favorite material is
common stranded, insulated hookup wire in whatever gauge is cheap at
the local surplus outlet or sitting under a table at a hamfest.  I arrived in
one town in Alaska and headed straight to the dump to see what I could
find for antenna material:  think I ended up with some wire unwound
from a TV deflection yoke coil.  As long as the loop isn't too small you can
get by with #22 or even smaller wire.

You can use TV coax as a feedline, or 300 ohm twinlead, or even twisted pair.
I've used speaker cable and zip cord when that was what was available, though
the losses tend to higher for any significant length.

If you don't have a balun, feed it without one.  I've fed 300 ohm twinlead
straight from the output coax connector on my rig (the lengths were right
so it had a low SWR).  For that matter, I've even put a banana plug on the
end of my wire antenna and stuck it into the center of the coax socket.

That's not to say that all of these are "good engineering practice", but if
they get you on the air when you wouldn't otherwise, then don't worry
about it.

An antenna tuner can be made from a variable capacitor (from a flea market,
or salvaged from an old AM radio) or two and a coil (which can be wound on
a pill bottle or toilet paper tube).  At one point I had an "antenna tuner"
for 20m through 6m using two bare wires running down the wall of my
garage and a handful of alligator clips:  I connected the antenna feedline,
coax to the rig, and a shorting bar across the wires in various positions
to get a match.

If you don't have enough radio books, check out the local library.

And get to know local hams - you may find one who can loan you books and
help you get started - and they might have a pile of wire in the scrap bin that
you can use.


A full-wave loop for 40m will have resonances on 20m, 15m and 10m, and it
makes a pretty good multi-band antenna.  But that takes about 144' of wire,
or about 36' on a side, and might not fit in your living room.  (Though you may
be able to drill small holes through the walls just below the ceiling and string
it from room to room.)  Smaller loops can be pressed into service on multiple
bands, but will require an antenna tuner of some sort.
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K5LXP
Member

Posts: 4439


WWW

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« Reply #5 on: January 10, 2013, 05:54:45 PM »

I have decided to go with a loop around our living room ceiling
I am looking for some advice on wire to use, baluns, etc. 

The elephant in the (living)room is not the wire, feed method or any matching devices.  It's the structure, which will have much greater influence on your success than whatever antenna configuration you will try.

Put another way, the materials choices you make won't make or break the success of your plan.  If it turns out you're living in a faraday cage, the most optimum antenna design won't change that.  Conversely, if your building is relatively RF transparent and EMI quiet, then even a marginal antenna will have some success and you can optimize from there.

WB6BYU's advice is sound.  Wire is cheap.  Start experimenting with something, anything.  You may discover a configuration that works "well enough" for now without investing in the hardware required for a very specific design.   In other words don't go nuts with detailed antenna design until you have some confidence your installation location has some chance of success.


Mark K5LXP
Albuquerque, NM


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