Performance of the ROOMCAP Antenna:

There are many antenna books where you find:
You need "much wire in the air" in order to obtain an efficient antenna.
Short antennas have an efficiency of 1 to 5 percent ...
Now the time has come to revise these statements!

The radiator length was 3m and the antenna height was 1.5m above ground,
mounted on the car, with 60 W PEP on 160m:

Date: Thu, 31 Aug 2006 22:57:42 +0200
From: Heino Held
To: hb9abx (at) tiscali.ch
Subject: Mobilantenne oder Festantenne

Hallo Felix,
nach unserem tollen QSO auf 160m waren Peter (DL1BLD) und ich (Heino, DJ5ER)
total erstaunt mit welch einer tollen Feldstaerke Du in Bremen angekommen bist.
Wie man eine solche Antenne bauen kann moechten wir gerne wissen (auch fuer die
anderen KW-Baender).

73 aus Bremen von Peter (DL1BLD) und Heino - DJ5ER

Translation:

Hello Felix,
after our fantastic QSO on 160m we (Peter,DL1BLD)
and I (Heino, DJ5ER) we were completely surprised
with what a strong field strength you arrived in Bremen.
We would like to know how such an antenna can
be built (also for the other HF bands).

73 from Bremen .... (QRB = 600 Km)
--------------------------------------------------------------------

5th September 2006:
Now I have reduced the length of the radiator to 2m = 1.25% of the wavelength,
and I still get the same good reports, as can be seen on the email I received after a few
fine contacts last night. Still with 60W PEP, at the border of the city, antenna mounted on the car:

Hello Felix.
Congratulations for your antenna work.
You are the first mobile station on 160 meters for me.
Even you are stronger as the Germans on 160 meters.
I give you on 1.862 Mhz S 9+15 db in the peak!!
The background noise level was S 8 during our QSO

Hope to meet you agn for next report and test.

Piet Schipper / PA0QRS (near Rotterdam)

Schipper mobiele Telecom
2931 LH Krimpen a/d Lek

-----------------------------------------------------------------------------------------

Such experiences show, that you can transmit with this small antenna
as effective, as with a 60m long wire, up in the air.

This is possible with:
- Radiating planes and not wires
- Differential feeding system
- Elaborated grounding system to minimise ground loss
- Perfect, low loss matching of antenna radiation resistance

With best 73s

Felix HB9ABX

Hi,
many of you have been waiting long time for user
evaluations of the RoomCap antenna.
Here follows two recent reports:

(posted by Felix Meyer HB9ABX)


They speak for themself.

-------------------------------------------------------------

Betreff: Bravo -Room Cap Antenna
Datum: Fri, 20 Oct 2006 18:59:12 -0700 (PDT)
Von: Paul Ragany VE3UNF ........
An: hb9abx.......

Hi Felix :

I have built the 20 meter version and it has reached more
than my expectations.
The antenna is fantastic - It is unbelieveable- I have been
comparing it to my G5RV and it out performs the G5RV .

Details:
Most tests were conducted between Tampa (Florida), my
location, and Toronto (Canada), VE3ZUH, over a distance
of 1700 km (1060 miles), using an FT-747 with 75 W output.

After two weeks, the results of my testing with VE3ZUH far
exceeded my expectations . VE3ZUH consistantly reports
2 s units better on the Roomcap compared to my G5RV.
I check in to the Maritime Net everyday on 14300.0 and
I consistantly get a strong 5 and 9 report from the net controllers
who are scattered all over the U.S. at various times of the day.
With the G5RV I get 5 and 8 to 5 and 9 reports.

On DX on Oct 19th I talked to OH2BH and OT4A (Belgium) -
they report 5 and 9 for my signal and I receive them at 5 and 7 .
On Oct 20th talked to Rob -HA503 FIN -special event station
in Hungary -he reports a 5 and 9 and I receive him at 5 and 7.
The G5RV was hearing 4 and 3to 5.

On receive, I average about 2 s units better about 50% of the time.
The signals are the same about 25% of the time and the G5RV
is about 2 s units better the other 25% of the time. I attribute that
to the 180 directionality if the G5RV ( north/south).

Thanks for everything and we'll keep in touch, 73

Paul A Ragany VE3UNF

PS: The G5RV is 2 x 15,8 m about 9m above ground.
The RoomCap has a radiator of 1,5 m length,
installed on a wooden stand 1,2 m above ground.

---------------------------------------------------------------------

Betreff: hb9abx antenna
Datum: Sat, 21 Oct 2006 15:52:40 +0200
Von: jeveraert ON6EJ@.......
An: hb9abx@.......

Hello Felix,

On my way back from work (Italy) to home (Belgium)
I had some time to visit you in Basel.

I was searching for a good antenna that is small in size.
Thanks to the Internet, I came across your website where
you published some information about your newly designed
RoomCap antenna.

I expected to see a mobile antenna that performed well,
I have seen other portable and mobile antennae, so I have
an idea as to what I might expect.
What I have seen was an antenna that, due to it’s design,
looked a little bit bulky.
This (maybe) disadvantage ‘’look’’ was quickly forgotten
when we made the first QSO’s.

As simple as it can be, from the car with the TS50,
several qso’s were made.

No comparison with what I have experienced before
during other mobile HF operations.
Signal reports obtained were outstanding, even when
using a transmit power power of 10 Watts !

My impression of this antenna is very positive.
I’ve never seen any antenna performing like the one
you have on your car ! (taken into account the size of it)

I’m very glad that I’m now able to build my own.
Thank you for the good work !

Best Regards

Jan, ON6EJ

-----------------------------------------------

On Tue, 24 Oct 2006 21:16:21 +0000, Felix
wrote:

many of you have been waiting long time for user
evaluations of the RoomCap antenna.


We already have some old, but superlative evaluations from Wall Street
about Enron that are far more useful.

Comparison: RoomCap with EH-Antenna

The EH-antenna is offered as a compact, efficient short antenna.
The user reports about this antenna are very varying, from enthusiastic
to unusable.
Therefore, I was interested since long time to perform a comparison test
of the RoomCap with this antenna.

On Nov 30, 2006 we could do that.
Andy, HB9DWF is owner of this antenna, and he was willing to perform
a field test.
We installed both antennas in a free camp and tested exhaustively on 160m.

Comparing antenna: EH Venus from Arno (Italy, WIMO Germany)
Length = 2.5m, Diameter = 8cm / 12.5cm, Weight = 4.9 Kg
Test antenna : RoomCap 160m, radiator length = 3m, Diameter = 7,5cm
with top capacity

Both antennas were installed with about 30m separation, at a height of 1.5m
above ground, and connected via decoupled coax cable and coax AB switch to
the 100 W transceiver.

First, the SWR was checked:
It was found, that the EH antenna is very narrow, in contrast to the statement
of WIMO who says:
"due to the design the entire band can be used."
The acceptable bandwith of the antenna was found to be just 20 KHz (!)
with resonance at 1.860 MHz.
In contrast, the RoomCap can be used in the full band from 1.800 to 2.000
with a VSWR 1:1, without using a tuner.
This problem complicated the testing somewhat, as we had to ask the
remote stations to change the QRG to 1.860 to allow operation of
the EH antenna on its best operating frequency.

The comparison tests began at 20.00hrs with a duration of one hour
and 20 minutes.
Until then we had 11 test contacts, and Andy said, that further QSOs
do no longer change the result. The result was clear.

In each contact the antennas were changed many times, and the remote
operators were asked to measure the signal difference.
All stations reported that the EH antenna is significantly weaker, and
they reported signal differences beween 2 to 4 S points.
The averaged signal difference was 3 S points.
Some stations were unable to measure the signal difference, as the
signal of the EH antenna was not readable.

The following stations participated in the comparing test QSOs:
F9EZ, I2BBJ, HB9ZY, F/HB9DHO, HB9BBM, HB9AGN, HB9COP,
HB9JMD, DL9FCP, DL1EFR, DB3MA.

Conclusion:
The test showed, that it is possible to make contacts with the EH antenna,
however the signal strength in comparison to the RoomCap antenna is
about 3 S points weaker.
(18 db correspond to a power relation of 1:63).
This "good result" is obtained only, if the antenna is operated within
20 KHz of the resonant frequency. If the antenna is used outside this
frequency range, an additional signal loss of 1 S point and more is to
be expected ...


Felix Meyer HB9ABX

Felix wrote:

Comparison: RoomCap with EH-Antenna

The EH-antenna is offered as a compact, efficient short antenna.
The user reports about this antenna are very varying, from
enthusiastic
to unusable.
Therefore, I was interested since long time to perform a comparison
test
of the RoomCap with this antenna.

Now, an additional comparison was made,
now between RoomCap and Magloop antenna.

Since long time it was my desire to compare the RoomCap antenna with a
good
magnetic Loop antenna.
On November 30th 2006 this test took place.
The test was assisted by Edy, HB9EBG.

Comparing antenna = Magnetic Loop, 85cm diameter, 35 mm diameter of
tube, copper tube, silvered, with Annecke butterfly capacitor with
remote tuning, in vertical position.

Test antenna = RoomCap for 20m, 5cm diameter, length of radiator =
150cm, without top capacity.

Both antennas were placed at the same height (150 cm above ground) in a
free field,
using the same 100 W transceiver, and adjusted to VSWR 1:1.

In total, 13 comparing QSOs were conducted in the time between 13.30h
to 16.00h.
In each QSO the antenna was quickly changed many times and the remote
station
was asked to indicate the average signal strength difference between
the two antennas.

In all contacts the RoomCap was reported clearly as the stronger
antenna, where the
smallest reported difference was 1 S point and the largest difference
was 5 S points.

Here follows the list of the reporting stations with the indicated
difference in S points.

YO5PDW + 1
LY3ZM + 3
RU6AH + 1
UA3AIU + 1,5
YO3AJN + 2
EA8BRW + 2
LY2SP + 4
UR0EA + 2
YO4AAC + 1
UT8NF + 1
YO6KSU + 2
UR5HDE + 5
SV0XBA + 2

This corresponds to an average difference of 2.11 S points.
An S point is defined as 6 db, resulting in about 12 db advantage.
(It is clear, that the receivers many times do not follow exactly
this definition, but in the average this may be close enough.)
In other words:
The RoomCap radiates about 15 times stronger than the Magloop.
(15 times the power).

Felix HB9ABX

Felix,

I'm surprised over this test...

What you are implying but not writing is that your RoomCap doesn't work as
well as an EH on 160m... I don't think that was what you intended... Hehe

Go home and do some basic math will you... The 160m EH need to be mounted
1/4 of a wavelength up while your RoomCap seems to be a vertical, able or
even meant to be used from groundlevel...

If, as you claim, the EH is only 2 S units down? Wow! That's good - even
absolutely bloody excellent! Well done EH! Unless the compared antenna is
crap of course! And as I have not seen any building description on the
RoomCap yet, who can tell...

If that EH where to be mounted at it's design height, you would have won at
least 3 to 6dB signal strength, equal to 1 to 2 S units.

Also, the bandwidth of the EH suffers when mounted wrong ( to low ).

Why can't these testers RTFM before setting out to prove function or
no-function of whatever gadgets they want to test?!
It's clearly stated about the mounting height!


However!!!!!

I'm very concerned over your statement about only one (1) S unit down if you
rx/tx outside the EH design frequency ( bandwidth ).

My EH's ( proper STAR's ) are shortcircuits when outside the bandwidth! This
is why they suppress TVI/RFI and harmonics in general as well as preventing
the coax to radiate ( one of the reasons anyway ). If described in S units,
the STAR is down 7 to 9 S units ( well outside the 3dB bandwidth )if
operated outside the bandwidth. It just goes quiet and the bandnoise just
vanishes - exactly like the shorted coax it just became...

You just told me the 160m EH you tested radiates from the coax?! As you only
had 1 S unit down outside the bandwidth. Bad bad bad! Was that an EH at
all?! Or just a short fat dipole?

And guess what... All the EH documentation are available on the net for hams
to try... without charges and fees...


//Dan, M0DFI

Felix wrote:
...

Felix:

Personally, I have a use for a small antenna. One which I can chuck
into my trunk and take along on quickly planned days away in the wild.
I have used the EH and got it up to good heights using a cord and
slingshot. It is not an efficient antenna in accepted terms. The good
match it provides over a good bandwidth and small size makes it perfect
for some of my adventures though. Hoisted high in a tree at the 11,500
ft elevation makes it look good to me; good to at the 9,500 ft elevation
while I fly fish mosquito lakes and have a bit of chat. Efficiency is
in the eye of the beholder.

Put paying for a CD to show me how to build another of these "dummy load
antennas" just doesn't float in my book ...

Regards,
JS

Felix wrote:
...


Dummy load antennas are all over, this is one link I stumbled upon
today, good pics.

http://guests.antennex.com/rooms/hws/ws0900/dda_rf.htm

Regards,
JS

John Smith wrote:

...


That didn't work, so here is yet another example:

http://home.comcast.net/~ac9ts/pdf/M...rt_english.pdf

JS

John Smith mentioned the Microvert antenna, which I know
very well.
I made an extensive comparison of the RoomCap (hb9abx)
against Microvert, and was using the best Microvert available
(MV-500) for 40m.
Test at same location, both antennas at same height in
A-B configaration.
Test was performed by many rapid changes between the
two antennas, and the remote station was observing
the signal strength.
Result was, that the RoomCap was 2 s-points stronger
in average, in receiption as well as in transmission.
Rember that 2 s-points correspond to 12 dB.
A very clear result.
73s
Felix HB9ABX