I just purchased an Icom AH4 antenna tuner and intend to use it to feed a 28
foot length of wire in a narrow attic crawl space.

I know the tuner needs to be grounded and wonder whether a ground wire
connected to an AC outlet ground is effective somewhat as an RF ground in
this circumstance. I hesitate calling attention to any antenna wiring by
running a heavy wire down the outside of the condo.

The other alternative would be to try and load a 28 foot dipole using one
side (14') connected to the ground on the tuner. I just don't know if this
setup would load well on too many bands.

Anyone have any ideas?

Myron wrote:
The other alternative would be to try and load a 28 foot dipole using one
side (14') connected to the ground on the tuner. I just don't know if this
setup would load well on too many bands.

Anyone have any ideas?

That arrangement should load fairly well on 20m-10m.
--
73, Cecil, W5DXP

- The dipole wires don't have to be straight. If you zigzag each
side of the dipole back and forth across the width of the attic
space a couple of times you can probably increase the length of the
wires significantly, and improve the tuner's ability to load up the
wires onto the lower-frequency bands.

Dave,

I will definitely add a choke balun.

How much zig zagging do you think I could get away with without introducing
factors that would seriously degrade performance? My attic crawl space is
about 3 feet wide, 4feet high pitching down to the floor and 28 feet in
length. I imagine I could easily fit a 33 foot dipole in that area to work
20M.

Thanks for the info.

Myron

Dave,

I will definitely add a choke balun.

How much zig zagging do you think I could get away with without introducing
factors that would seriously degrade performance? My attic crawl space is
about 3 feet wide, 4feet high pitching down to the floor and 28 feet in
length. I imagine I could easily fit a 33 foot dipole in that area to work
20M.

I'd think that you could zig-zag the wire back and forth at an angle
of 45 degrees to the long axis, a foot or two above the floor, without
causing substantial degradation of performance. If you don't end up
needing to zig-zag that much to fit the 33 feet of wire into 28 feet
of space (and you probably wouldn't), zig less frequently!

Take a look at the discussion at http://www.cebik.com/zzdd.html for
some further ideas.

I imagine that your antenna's performance is likely to be set mostly
by the amount of power you can use without causing RFI/TVI due to the
strong RF fields in close proximity to household wiring. The slight
reduction in antenna efficiency isn't likely to matter very much.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave,

Thank you once again.

I'm going to run a maximum of 100W with my Icom 725 and assume (hope) that
the power level is low enough to avoid problems.

The website you directed me to is pretty darn nice. I've done antenna
searches on Google and never came across this worthwhile info. I'll try to
digest the material.

I wish the ARRL antenna handbooks would explain things as simply. When I've
used their manuals for reference (I have a fair library), I find that my
eyes begin to glaze over. I bought their "Stealth Radio" book, hoping for
ideas, but that was way too basic. I did come across some useful websites
using Google, but alot of the information was duplicated so there was not as
many useful ideas as I had hoped for.

You've been the biggest help.

Myron W2EDY

I imagine that your antenna's performance is likely to be set mostly
by the amount of power you can use without causing RFI/TVI due to the
strong RF fields in close proximity to household wiring. The slight
reduction in antenna efficiency isn't likely to matter very much.

Dave,

Thank you once again.

You're most welcome. The real thanks go, of course, to the folks who
write those various wonderful educational pages. I've learned a very
great deal over the past year or so.

I'm going to run a maximum of 100W with my Icom 725 and assume (hope) that
the power level is low enough to avoid problems.

Ummph. You may have problems there.

Anecdotal evidence suggests that in a lot of residential situations,
running more than about 25 watts HF is fairly likely to create a
situation known as "fundamental overload" in nearby consumer-grade TV
tuners and FM radios. The strong RF signal saturates the tuner
electronics, forcing them into nonlinear behavior. It doesn't help
even if your RF signal is perfectly "clean" and has no harmonic
content (an impossible ideal) - even a pure signal will result in
these TVs and other such devices misbehaving (herringbone displays,
etc.).

Adding a high-pass filter at each affected TV set's RF input, and
adding choke filters to the power cord and A/V cables, can help a lot.

The same is true for telephones. I know that when I key up a 20-meter
PSK31 signal at about 20 watts, my wife can hear it on her telephone
(I really need to add some ferrites) and my antenna's outdoors up at
about 25'.

With an in-the-attic antenna you may need to keep power down to 5-10
watts to avoid interference.

That's the bad news. The good news is that cutting power from 100
watts to 10 is only 10 dB, which isn't even one S-unit on a typical
amateur receiver. Under most circumstances it won't make a big
difference in how audible your signal is. There's one particularly
skilled operator in my area who regularly breaks CW pileups to South
Pacific islands, running only a couple of watts, from an HF mobile rig
in his car. [Maybe if I play around with this stuff for a few decades
I might pick up a fraction of that skill... I should be so lucky!]

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

If you think 10 dB is insignificant, try to explain why to the person
who's proud of his 7 element single band Yagi mounted on a 1.3
wavelength boom, which is how much you need to get 10 dB gain over a
dipole. Or the person who just bought a kW amplifier to drive with his
100 watt rig.

I've yet to see an S-meter with units greater than about 6 dB. Less than
this is much more typical. The S units on my Icom 730 vary from 1.3 to
4.0 dB, depending on where on the scale you are. A 10 dB signal change
will move the meter from S-2 to S-7.

This isn't to say you can't work a whole lot of stations with 10 watts,
or a 100 watt rig into a 10% efficient antenna -- or even with one watt.
But you will notice a difference when you increase or decrease your
power 10 dB.

Roy Lewallen, W7EL

Myron wrote:
That IS good news and something I'll have to keep in mind. That's the kind
of information that gets listed in a chart somewhere about transmitting
theory and is easy to forget when so many people seem overly concerned about
tweaking antenna efficiencies and lowering SWR by the smallest percentage
points.

Myron

. The good news is that cutting power from 100

watts to 10 is only 10 dB, which isn't even one S-unit on a typical
amateur receiver. Under most circumstances it won't make a big
difference in how audible your signal is. There's one particularly
skilled operator in my area who regularly breaks CW pileups to South
Pacific islands, running only a couple of watts, from an HF mobile rig
in his car. [Maybe if I play around with this stuff for a few decades
I might pick up a fraction of that skill... I should be so lucky!]

Dave,

Can I come back to a point you made earlier? You wrote.......
- Add a choke balun where the coax reaches the tuner (just take 8-10'
of the coax, and wind it into a loop 8-10" in diameter and use
tiewraps to hold it together). This will help maintain balance
between the two sides of the dipole.

There is not enough supplied Coax available to make the choke balun and
still reach my transciever. There are no markings on the cable supplied by
Icom but it looks like they use RG8U. I haven't purchased cable in many
years and seem to remember that insulation and shielding varies by
manufacturer. I'll look for maximum shielding but wonder whether foam
insulation is OK for the choke balun?

Somewhere in the back of my mind I remember seeing something about the cons
of foam insulated coax. Am I getting paranoid?

Myron

Can I come back to a point you made earlier? You wrote.......

- Add a choke balun where the coax reaches the tuner (just take 8-10'
of the coax, and wind it into a loop 8-10" in diameter and use
tiewraps to hold it together). This will help maintain balance
between the two sides of the dipole.

There is not enough supplied Coax available to make the choke balun and
still reach my transciever. There are no markings on the cable supplied by
Icom but it looks like they use RG8U. I haven't purchased cable in many
years and seem to remember that insulation and shielding varies by
manufacturer. I'll look for maximum shielding but wonder whether foam
insulation is OK for the choke balun?

Sure, it should be fine. As with any coax, you should check the power
rating (lest you arc the cable or overheat it in use, but you
shouldn't have this problem with RG8 at reasonable power levels).
And, for the lengths we're talking about here, and at HF frequencies,
I suspect that RG8 may be overkill - you could use RG8X "mini" coax
and the losses would be quite tolerable.

Somewhere in the back of my mind I remember seeing something about the cons
of foam insulated coax. Am I getting paranoid?

Well, I believe that foam-insulated coax may be a bit more prone to
wick up water if you don't seal the connectors properly and the rain
starts to fall ;-)

For indoor applications this shouldn't matter. Just buy a 10-15'
piece of RG8 with PL-259 connectors on it, use a barrel adapter to
connect this to your existing run of coax, roll up the choke balun,
and you should be fine.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!