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Reviews For: Sommer T-25

Category: Antennas: HF: Verticals; Wire; Loop

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Review Summary For : Sommer T-25
Reviews: 4MSRP: 260
Description:
Terminated Frequency-Independent Vertical
Product is not in production
More Info:
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
0044.3
K2DC Rating: 2002-09-02
Forget anything below 30M! Time Owned: 0 to 3 months.
I am a 20+ year Ham, and a degreed antenna
engineer by trade. I was intrigued by the
advertized efficiency of 70% down to 80M and
the advertized ground independance, because I
was looking for something better than my
40/80M inveted vees at 38' for DX (with no room
for a full-sized vertical and ground plane).
I installed the antenna about 6' off the
ground, with a ground rod. DX signals on 40M were
10+ dB below the wires, and signals on 80M were
40+ dB below the wire. I measured power into the
antenna, and power into the load on all bands,
and found the efficiency less than 44% on all
bands except 20M, 30M, 10M and 6M, and only 10%
on 80M (without accounting for any gound losses).
Those frequencies happen to correspond to about
1/4, 5/8, 3/4, and 5/4 wavelengths long.
I emailed a description of the installation
and the measurement results to Alf Sommer. His
response came in two emails;

"Please remove the grounding of the radials. They
can not be DC-grounded. A dipole grounded with
a ground rod on just one side would be the
same...."

A dipole grounded on one side is called a
half-sloper, and as long as the grounded leg is
not an odd quarter wavelength long, they work
great. I used one for years, and so have many
others.

In his second email:

"Some general information on the T-25: This
antenna is a half-lambda ground independent
radiator and comparable to the W8JK Folded Monopole."

The W8JK Folded Monopole has the return
wire GROUNDED, not loaded. I asked if he was
aware of anyone grounding the return wire to
use it as a true folded monopole, and got no
response.

"Its length of 25 ft + the additional 8 ft of the "radials" gives a total length of 33 ft for
the whole antenna system and makes a full-size
radiator for 20 meters - fed like a Windom
antenna."

A Windom is fed off-center at about 35% of
total length from the end at the lowest
resonant frequency to provide a feedpoint
impedance of 200-300 ohms at even and odd harmonic frequencies. If this is supposed to
be fed like a Windom, why is it fed 24% from
the end?

"Suggestions: As mentioned in the T-25
instructions, please remove the parallel wire
from the tuning transformer. This makes the
antenna a perfect no-loss-monobander for 20
meters with a typical bandwidth of 2 MHz
(SWR 2:1 at the end of the band) You can
compare your 20 m - T-25 now with your other
antennas. It must display SWRs in the 20 m
band of 1.5 : 1 or better 14.00 to 14.350 MHz.
Please note that the polarizations may be
different! I recommend to test with far-DX
stations only (Europe etc.- not inside US)"

I had already tried this before I received
his second email. I found the match very good
over 20M, and DX stations about 1 S-Unit below
my C3-SS at 40' (which is where they should be).
DX signals on 30M are about 1 S-Unit above my
wire antennas.

In all fairness, if you're looking for a
frequency-independant antenna with space
limitations for operation on 30M, 20M or 10M,
this could be the one.

If you're looking for anything better than
a dipole on 40M or 80M, forget it.
K4CA Rating: 2000-05-13
Very well engineered and built antenna. Works very well. Time Owned: more than 12 months.
Highly recommend the T25 if you can't have a directional antenna. In use here for 15 months without a problem. I am constantly surprised at the contacts I make with this vertical. After using yagis, loops ect, this is too easy.

N3SKO Rating: 2000-04-02
Excellent Antenna! Time Owned: unknown months.
I utilize the Sommer T-25 for Automatic Link Establishment networks - the no-tune feature is a
god-send, since frequencies change with each contact. The ALE nets that I operate on (FEMA,
SHARES) have very wide frequency ranges (4-26 MHz), and this antenna performs reasonably
well on all of them.

Thumbs up!
W3ZVT Rating: 1999-10-08
Well worth the money Time Owned: unknown months.
Have had the Sommer T-25 up now for over four years and am completely satisfied with the antenna. No traps, no tuning, I can come up on any frequency and be assured of good performance and SWR. Do a lot of QRP work and I never fail to get good reports with this
antenna. It's the first antenna I switch to when I go on the air.