Indoor TC2M/G8JNJ broadband shortwave antenna tested

Just playing "catchup" and looking at these links.
Interesting reading :-)

BR Harry

Admin wrote:Hi Glenn,
Thank you very much for the information.
...
I was a little sceptical because, even with a resonant antenna element, only 1% to 2% of each cycle of RF is actually radiated.
...
Very best regards from Harry - SM0VPO

Hi Harry

Look at these efficiency curves for the T2FD:
http://www.korpi.biz/T2FD_NVIS.pdf
Quote: "...
We tested it over average ground type; only minor changes were seen on simulations and SWR measurements.
..."

411 TERMINATED FOLDED DIPOLE ANTENNA:
https://www.codanradio.com/wp-content/uploads/Codan-411-Terminated-Folded-Dipole-Antenna_Screen.pdf

http://www.eham.net/ehamforum/smf/index.php?topic=68475.0
Quote: "...
That is a short Wideband Terminated Dipole. Yes I have built, modeled, and written about this type of antenna. The Buxcomm specified gain is at 28 MHz. These antennas are simple to model with NEC-2:
T2FD radiation efficiency:
80 meters: 4%
40 meters: 16%
20 meters: 25%
15 meters: 35%
10 meters: 55%
..."

Hi Glenn,
Thank you very much for the information.

At the moment I am in Spain and have no access to workshop or any other facilities. Buy I would be very interested in doing some tests, based on the links you gave.

My brother once told me of an antenna he had that was "near perfect on all bands", and did not require any tuning. At 14MHz it was quite good, but at all other frequencies it was steadily worse in performance, but the VSWR was always better than 1.6 : 1 which I thought was unbvelievable.

It turned out that the was nothing more than a 5m pole fed by some form of circulator on TX. All reflected power was diverted to a third port and burned in a dummy load. As a result he had a near-perfect VSWR, but the actual radiation was rather poor.

TX and RX was reciprocal since the RF routing was not active on receive.


I was a little sceptical because, even with a resonant antenna element, only 1% to 2% of each cycle of RF is actually radiated. But due to resonance, the instantaneous power stored in the resonant circuit can be 50x to 100x the applied power, so 1% of 10,000% = 100%. If an antenna can indeed radiate 100% (25% or more is good) of the applied power then I would like to learn more.

When i return to Sweden I will look at the links as this could be a very interesting subject.

In the millitary we used multi-wavelength antennas to make high-power, directional antennas for the HF bands communications. They were several wavelengths long and the far end was terminated in a huge, resistive dummy load to prevent any reflected power. But these were really huge antennas, and we used to refer to the antenna site as the "Aerial Farm". One such site occupied a large part of an island.

But techniques change. Today we have fractal and meander antennas that are perfect for small size and the higher frequencies.

Very best regards from Harry - SM0VPO

Hi Harry

Actually I did test, but not with calibrated equipment. Please note: My surroundings are filled with buildings and the antenna is placed indoor and is surrounded by walls with some metal in them - and windows with infrared reflecting layers. It is almost impossible to make an unbiased antenna measurement?

Please also note that I am not able to raise a vertical or horisontal dipole with a length of ca. 75 meter for the 160 meter band. My indoor limits are 4 meter high and maybe 8 meter horisontal width at 3 meter above ground.

My test connections/QSOs and SWR measurements are described there (please click the link and scroll down to #13 and read onwards):

Some time later I built my own four meter high Indoor TC2M antenna and made a few local connections on most shortwave bands - including 160 meter - and the VHF 6 meter band. The four meter high TC2M should also work on VHF 4 meter band (70 MHz). Please read about it from #13. Later; #16 #17 TC2M is measured with a two port DG8SAQ VNWA 3E vector network analyzer. Yes the TC2M antenna has two 50 ohm ports, if the output port 450ohm is transformed to 50 ohm (in danish):
http://ham.brugtgrej.dk/forum.php?mode=thread&obj=66497


G8JNJ's own tests with calibrated equipment are here:

Then the 10 meter high TC2M/G8JNJ broadband shortwave antenna was found:
http://web.archive.org/web/20150529061427/http://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf

Hi Glenn,
It is an interesting technique. I would be interested to see how it performs when compared to a resonant antenna in similar environments.
I mean to measure the radiation level at, say, 50 metres distance.

If you have one then is it easy for you to do some tests? Probably not so easy since you would need to have two antennas.

BR Harry

I have not tested this, but TC2M antenna seems to show the principle:

Do not use a traditional narrowband antenna tuner (including an antenna coil or capacitor) in-front-of/before the feeding-point of an antenna because it is normally inefficient, but an efficient broadband transformer (unun, balun, unbal, balbal) might be used in front if needed, so the maximum current is at the antenna feed point (whether the antenna is short or long).

Place the traditional (typically inefficient) antenna tuner after the antenna so a maximum amount of energy has left the antenna before converting the rest to heat - assuming a two port antenna :-)

-

There is a bonus if you "remove" the standing waves on the outside of your antenna (e.g. as in TC2M and TWA) - especially if longer than 1/2 wavelength at higher frequencies. The bonus is that unwanted side lobes is suppressed, because any antenna lower current points (even null points) is suppressed.

The TC2M current travel up the monopole on the outside - and if any energy (current) is left at the top - it travels into the inside of the monopole (coaxial-like) and is absorbed by the dummy-load ("broadband antenna tuner"). When the current travel inside of the monopole, the current will not be EM-visible to the outside "world" and therefore do not interfere with outside monopole radiation field.

Hi Glenn,
As you say, it is a common misconception that an antenna must be resonant.
Interesting that most compact antennas are resonant to get the efficiency up, otherwise the small size can be a bit limiting, or so I found.

I once blew up a 6146 TX tube by loading into a 1km long electric fence, 1m off the ground. Non resonant, but the sheer length made radiation extremely good. Like a fool I was more interested int he forward power than the Anode current of the 6146. melted the glase and blew a hole in the side :-)

BR Harry

Hi Harry

Some time ago I tried an indoor 2 meter high Yaesu ATAS-120 antenna with built-in motor to tune it - to slow for me.

Appetizer:

info about "non-resonante":
http://www.tapr.org/~n5eg/index_files/Broadband%20HF%20Antennas.pdf
Citat: “...
Misconception: An antenna (dipole or loop) must be resonant to work well.
– Antenna does not need be resonant to work well
…"

Then the 10 meter high TC2M/G8JNJ broadband shortwave antenna was found:
http://web.archive.org/web/20150529061427/http://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf

Some time later I built my own four meter high Indoor TC2M antenna and made a few local connections on most shortwave bands - including 160 meter - and the VHF 6 meter band. The four meter high TC2M should also work on VHF 4 meter band (70 MHz). Please read about it from #13. Later; #16 #17 TC2M is measured with a two port DG8SAQ VNWA 3E vector network analyzer. Yes the TC2M antenna has two 50 ohm ports, if the output port 450ohm is transformed to 50 ohm (in danish):
http://ham.brugtgrej.dk/forum.php?mode=thread&obj=66497

Please note #14; the 10 meter high version TC2M with good groundplane/grounding is much more efficient than a 75 meter long dipole for the 160 meter band at 6 meter height. There are more examples that TC2M is better and why.

-

Note:

An antenna do not need to be long in terms of wavelengths to be efficient. The smallest quadlong is 0,136 wavelengths long! See "Table 1: Data of 2-m-Oblongs with 6-mm-Elements, lengths in lambda":
http://www.qsl.net/dk7zb/Quadlong/theory_dk7zb-quadlong.htm

So most of a 1/2 wavelength dipole is not used for sending EM-waves. So e.g. 0,136 wavelengths should be enough - where the currents are high.

Why an Antenna Radiates:
http://www.arrl.org/files/file/Technology/tis/Why%20an%20Antenna%20Radiates.pdf
Quote: "...
And an accelerating or decelerating charged body, be it an electron or a pithball, is a source of electromagnetic radiation.
..."