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"Mark" == Mark Keith writes:

[...]

Jack I have an MFJ Versa Tuner II which has a power meter. It's not
Jack laboratory certified, but the needle does go all the way up to
Jack 100 when I tune up and transmit.

Mark Well, you know the radio works...

At least enough to move that needle, or to come in on my friend's
DC-to-daylight receiver as I previously mentioned.

Jack I can't get the wire any higher than it is right now at this
Jack current location. This is pretty much the best I can do, and
Jack this little antenna already totally fills my yard and the yards
Jack of each of my neighbors (with their permission). It's a
Jack multiband fan dipole with three pairs of legs, cut for 40, 20,
Jack and 10.

Mark Your antenna is *very* efficient on those three bands, unless
Mark you have coax or connection problems and power is not making it
Mark to the antenna. BTW, the 40 legs will work 15 ok, if you tweak
Mark the match with the tuner...Will be pretty efficient on 15 also
Mark as a 1.5 wl dipole.

Providing the wires haven't stretched too much over the past six
months, or something else that might be wrong. Oh, and yes, all of
the dipole legs are coplanar, and I can't change that, so I'll have to
be careful when I tune them.

Jack My current goal is to acquire a noise bridge and see where the
Jack antenna resonates, then trim the antenna as necessary until it
Jack resonates in the right places.

Mark Good idea. You shouldn't really need the tuner.

I acquired an MFJ noise bridge with the help of Dave Platt, and here
are the results from some rough measurements at the rig (not at the
antenna!):

Frequency Depth R X Expander Resistance Reactance Impedance
3.750 4 D +25 No 122 28.67 125.32
7.150 2 A/B -25 No 14 -20.17 24.55
14.175 0.5 A/B +175 No 14 30.85 33.88
21.225 4.5 E +150 Yes 903.88 663.97 1121.54
28.850 0.5 A/B -100 No 14 -38.54 41.00

"Depth" is a rough estimate of how deep the null was when the
measurement was taken -- my rig has a 0-10 scale and the measurements
began when the noise was around 7 or 8, usually. The next three
columns were my readings, and the final three columns are the reported
values, in ohms.

The first thing to note is that the readings which resulted from the
deepest nulls are the readings which provide the most reasonable
impedances. This tells me that I'm getting sensible readings,
although I do need more practice with the device -- it's terribly
twitchy.

I plan on trying to find the resonant frequency of the antenna over
the next couple of days, with the goal of shortening (or lengthening)
the individual wires this weekend.

Jack After that, I'll look into feedline length modifications as
Jack necessary.

Mark Should be unneeded. If coax length radically varies SWR, you
Mark need a 1:1 balun or choke to cut radation from the shield.

I have two chokes in my feedline currently -- one about a foot from
the antenna feedpoint consisting of eight or nine turns of coax about
an air core (a Folger's coffee can was used for wrapping), and one
about a foot from the rig consisting of three large type 43 ferrite
toroids with three loops of coax passing through all three toroids.

Jack Hopefully those two approaches will resolve my current issue.

Mark Actually, I don't think you have a problem, assuming no coax or
Mark connector problems.

When conditions change for the worse with no obvious reason, I start
to consider the possibility that a problem exists. I can't blame
sunspots for everything, so I'm looking into how my antenna may have
changed since it was installed.

I just completed another test of my antenna. I set the antenna tuner
to "bypass" so I could use its SWR meter without affecting the
tuning. Then, for each of the five bands I want to use, I tuned up on
the dummy load, then switched over to the real antenna and checked the
SWR. Here's the results:

Frequency Dummy Antenna
3.750 1:1 infinity
7.150 1:1 2.5:1
14.175 1.05:1 3:1
21.225 1.1:1 3:1
28.850 1:1 1.9:1

There may be a correlation between these SWR measurements and the
impedance values shown above -- the three bands which had lower
impedance values also have lower SWR values, but none of them look
particularly healthy.

Mark Does the receive noise level, and signal levels sound fairly
Mark normal, or dead?

My experience aside from working from this location is limited to
Field Day, which isn't really helpful. On some bands I get tons of
receive noise, on others I get less.

Mark I think the main problem is trying to work locally using ground
Mark wave, with an antenna that is poorly suited for that. But, you
Mark should usually be able to work 40m in the day, being it's mainly
Mark NVIS.

NVIS is still a mystery to me, and I need to learn more about it.

Mark 20 miles is a long way for a low horizontal dipole to work
Mark locally without the help of skywave. A purely horizontal antenna
Mark has no groundwave, if no vertical feedline radiation, etc. It
Mark has a space wave, but it's going to be hard to work 20 miles
Mark over the noise. If both of you had verticals, it would probably
Mark be easy. As far as comparing antennas, all you have to do is use
Mark a antenna switch, and see which is best on receive. Operation is
Mark reciprical 98.8 % of the time, so a transmit test is unneeded.

I don't have any antenna against which to compare this one, though.

Mark You should be having no problems working 40m in the day, or even
Mark 20m to stateside stuff. 10m local will be very tough, but you
Mark should be able to work some skywave.

I'm currently unemployed, so I've got time for this kind of testing.
Tomorrow, I'll try 40, 20, and 10 in the morning (eight to ten), in
the afternoon (two to three), at sunset (five to seven), and at night
(nine to ten). I'll post the results tomorrow night.

Mark A vertical is much better for 10m local. 20 ft high is high
Mark enough to work for medium distance skywave. Maybe not a
Mark barnburner, but it should be working for general gov work...I've
Mark run many lower than that when camping, and had no problems. If
Mark you can't hardly work *anyone*, I would check your connections,
Mark and coax , etc.

I've already talked about having checked connections. I really think
the next step is to change the lengths, but I want to make sure I
understand the noise bridge's results first.

Mark Also, if you use the tuner for now, use the bare minimum
Mark inductance to get a usable match. That will help reduce tuner
Mark losses, which can climb to 20% or so if too much coil is used.

I've always done that, but mostly because that's what the antenna
tuner documentation says to do, not because I knew why. :-)

Mark I would eventually tune the antenna up, and dump the
Mark tuner. There is no real need for it, unless you go off far from
Mark where you normally have it tuned. IE: work some CW when the
Mark antenna is tuned for the fone band. MK

That's exactly why I bought the tuner -- that, and so I'd have an SWR
meter in the shack.

Jack.
- --
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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