RX ant low band

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RX ant low band

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Der kører en discution omkring RX ant på Topband refectoren
For dem der interserer sig for disse emner vil jeg anbefale subcribe til topband
Link nede i bunden

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Hi guys

I would like to share some papers from my good friend (SK) Dr Dallas was a great experimental guy that loved Mathematic and AM DXing,. Dr Dallas with a strong personality and seniority some times was hard to follow and some time the result of tests were not as planned, like the multi turn flags.

Dr Dallas interest was on MF 500KHz to 1600 MHz and some results are not the same on 160 or 80m. I can send the original paper attached if requested.

Flag Theory
Dallas Lankford, 1/31/09, rev. 9/9/09
The derivation which follows is a variation of Belrose's classical derivation for ferrite rod loop antennas,
“Ferromagnetic Loop Aerials,” Wireless Engineer, February 1955, 41– 46.
Some people who have not actually compared the signal output of a flag antenna to other small antennas have
expressed their opinions to me that the signal output of a flag antenna has great attenuation compared to those
other small antennas, such as loops and passive verticals. Their opinions are wrong. One should never express
opinions which are based, say, on computer simulations alone, without actual measurements. The development
below is based on physics (including Maxwell's equations), mathematics, and measurements.
Measurements have confirmed that the flag signal to noise formula derived below is approximately correct
despite EZNEC simulations to the contrary. For example, EZNEC simulation of a 15' square loop at 1 MHz
predicts its gain is about +4 dbi, while on the other hand EZNEC simulation of a 15' square flag at 1 MHz
predicts its gain is about –46 dBi. But if you construct such a loop and such a flag and observe the signal
strengths produced by them for daytime groundwave MW signals, you will find that the maximum loop and flag
signal outputs are about equal. Although somewhat more difficult to judge, the nighttime skywave MW signals
are also about equal.
Also, the signal to noise ratio formula below for flag arrays has been verified by man made noise measurements
in the 160 meter band using a smaller flag array than the MW flag array discussed below. Several years ago a
similar signal to noise ratio formula for small untuned (broadband) loop antennas was verified at the low end of
the NDB band.
The signal voltage es in volts for a one turn loop of area A in meters and a signal of wavelength λ for a given
radio wave is
es = [2πA Es /λ] COS(θ)
where Es is the signal strength in volts per meter and θ is the angle between the plane of the loop and the radio
wave. It is well known that if an omnidirectional antenna, say a short whip, is attached to one of the output
terminals of the loop and the phase difference between the loop and vertical and the amplitude of the whip are
adjusted to produce a cardioid patten, then this occurs for a phase difference of 90 degrees and a whip amplitude
equal to the amplitude of the loop, and the signal voltage in this case is
es = [2πA Es /λ] [1 + COS(θ)] .
Notice that the maximum signal voltage of the cardioid antenna is twice the maximum signal voltage of the loop
(or vertical) alone. A flag antenna is a one turn loop antenna with a resistance of several hundred ohms inserted
at some point into the one turn. With a rectangular turn, with the resistor appropriately placed and adjusted for
the appropriate value, the flag antenna will generate a cardioid pattern. The exact mechanism by which this
occurs is not given here. Nevertheless, based on measurements, the flag antenna signal voltage is approximately
the same as the cardioid pattern given above. The difference between an actual flag and the cardioid pattern
above is that an actual flag pattern is not a perfect cardioid for some cardioid geometries and resistors. In
general a flag pattern will be
es = [2πA Es /λ] [1 + kCOS(θ)]
where k is a constant less than or equal to 1, say 0.90 for a “poor” flag, to 0.99 or more for a “good” flag. This
has virtually no effect of the maximum signal pickup, but can have a significant effect on the null depth.
The thermal output noise voltage en for a loop is
en = √(4kTRB)
where k (1.37 x 10^–23) is Boltzman's constant, T is the absolute temperature (taken as 290), (Belrose said:) R is
the resistive component of the input impedance, (but also according to Belrose:) R = 2πfL where L is the loop
inductance in Henrys, and B is the receiver bandwidth in Hertz. When the loop is rotated so that the signal is
maximum, the signal to noise ratio is
SNR = es/en = [2πA Es /λ]/√(4kTRB) = [66Af/√(LB)]Es .
The point of this formula is that the sensitivity of small loop antennas can be limited by internally generated
thermal noise which is a characteristic of the loop itself. Even amplifying the loop output with the lowest noise
figure preamp available may not improve the loop sensitivity if man made noise drops low enough.
Notice that on the one hand Belrose said R is the resistive component of the input impedance, but on the other
hand R = 2πL. Well never mind. Based on personal on hands experience building small loops, I believe R =
2πL is approximately correct. What I believe Belrose meant is that R is the magnitude of the output impedance.
For a flag antenna rotated so the the signal is maximum, the signal to noise ratio is
SNR = es/en = 2[2πA Es/λ]/√(4kT√((2πfL)^2 + (Rflag)^2)B) = [322Af/√(√((2πfL)^2 + (Rflag)^2)B)]Es .
Now let us calculate a SNR. Consider a flag 15' by 15' with inductance 24 μH at 1.0 MHz with 910 ohm flag
resistor, and a bandwidth of B = 6000 Hz. Then A = 20.9 square meters and SNR = 2.86x10^6 Es . If Es is in
microvolts, the the SNR formula becomes
SNR = 2.9 Es .
Any phased array has loss (or in some cases gain) due to the phase difference of the signals from the two
antennas which are combined to produce the nulls. This loss (or gain) depends on (1) the separation of the two
antennas, (2) the arrival angle of the signal, and (3) the method used to phase the two flags. Let φ be the phase
difference for a signal arriving at the two antennas. It can be shown by integrating the difference of the squares
of the respective cosine functions that the amplitude A of the RMS voltage output of the combiner given RMS
inputs with amplitudes e is equal to to e√(1 – COS( φ)) where e is the amplitude of the RMS signal, in other
A= 1

2 e2cost−costφ2dt=e21−cosφ
The gain or loss for a signal passing through the combiner due to their phase difference is thus √(1 – COS( φ)).
Let us consider the best case, when the signal arrives from the maximum direction. For a spacing s between the
centers of the flags, if the arrival angle is α, then the distance d which determines the phase difference between
the two signals is d = s COS(α). If s is given in feet, then the conversion of d to meters is d = s COS(α)/3.28.
The reciprocal of the velocity of light 1/2.99x10^8 = 3.34 nS/meter is the time delay per meter of light (or radio
waves) in air. So the phase difference of the two signals above in terms of time is T = 3.34 s COS(α)/3.28 nS
when s is in meters. The phase difference in degrees is thus φ = 0.36Tf = 0.36 f x 3.34 s COS(α)/3.28 where f is
the frequency of the signals in MHz. If additional delay T' is added (phase shift to generate nulls or to adjust the
reception pattern), then the phase difference is φ = 0.36(T + T')f = 0.36f(T' + 3.34 s COS(α)/3.28) . If the
additional delay is implemented with a length of coax L feet long with velocity factor VF, then the phase delay is
φ = 0.37f(L/VF + s COS(α))
where f is the frequency of the signal in MHz, s is in feet, L is in feet, and α is the arrival angle.
In the case of the flag array above in the maximum direction there are two sources of delay, namely 60.6 feet of
coax with velocity factor 0.70, and 100 feet of spacing between the two flag antennas. The phase delay at 1.0
MHz for a 30 degree arrival angle is thus
φ = 0.37 x 1.0 x (60.6/0.70 + 100 COS(30)) = 64.1 degrees.
Thus the signal loss in the maximum direction at 30 degree arrival angle due to spacing and the phaser is
√(1 – COS( 64.1)) = 0.75 or 20 log(0.75/2) = –8.5 dB.
Now comes the interesting part. What happens when we phase the WF array with dimensions and spacing given
above? The flag thermal noise output doubles (two flags), and the flag signal output decreases (due to spacing
and phaser loss), so the SNR is degraded by 14.5 dB to
SNR = 0.55 Es .
So a signal of 1.8 microvolts per meter is equivalent to the thermal noise floor of the flag array.
On some occasions, when man made noise drops to very low levels at my location, it appeared to fall below the
thermal noise floor of the WF array. By that I mean that the characteristic “sharp” man made noise changed
character to a “smooth” hiss. To determine whether this was the case, I measured the man made noise at my
location for one of these low noise events at 1.83 MHz.
To measure man made noise at my location I converted one of the flags of my MW flag array to a loop. The
loop was 15' by 15', or 20.9 square meters. I used my R-390A whose carrier (S) meter indicates signals as low
as –127 dBm. The meter indication was 4 dB. Then I used an HP-8540B signal generator to determine the dBm
value for 4 dB on the R-390A meter. It was –122 dBm. Now the fun begins. The RDF of a loop for an arrival
angle of 20 degrees (the estimated wave tilt of
man made noise at 1.83 MHz) was 4 dB. So now
man made noise after factoring out the loop
directionality was estimated as –118 dBm. Field
strength is open circuit voltage equivalent, which
gives us –112 dBm. I measured MM noise on the
R-390A with a 6 kHz BW. The conversion to
500 Hz is –10 log(6000/500) = –10.8, which
gives us –122.8 or –123 dBm. The conversion to
500 Hz was necessary in order to be consistent
with the SNR above which was calculated for a
500 Hz BW. The loop equation is es = 2πAEs
/lambda = 0.41 Es, and 20 log(0.41) = –7.7,
rounded off to - 8, so we have -115 dBm, or 0.40
microvolts per meter for my lowest levels of man
made noise at 1.83 MHz in a 500 Hz bandwidth.
This seemed impossibly low to me until I came
across the the ITU graph at right. Man made
noise at quiet rural locations may be even lower
than 0.40 microvolts per meter at 1.83 MHz. But what about the MW band? From the CCIR Report 322 we
find that the man made noise field strength on the average is about 10 dB higher at 1.0 MHz than 1.83 MHz,
which would make it 1.26 microvolts per meter at 1.0 MHz. Another 4 dB is added because of impedance
mismatch between the R-390A and the loop, which brings man made noise up to 2.0 microvolts per meter at 1.0
MHz. The RDF of one of these flags is about 7 dB, which lowers the man made noise to 0.89 microvolts per
meter. Observations in the 160 meter band do not seem to agree exactly with this analysis because flag thermal
noise has never been heard on the MW flag array. But it would not surprise me at all if the flag array thermal
noise floor were only a few dB below received minimum daytime man made noise and that measurement error
(for example, calibration of my HP 8640B) accounts for the difference between measurement and theory. Also,
observations with a flag array having flag areas half the size of the MW flag elements in the 160 meter band do
confirm the signal to noise ratio formula; in this case, flag thermal noise does dominate minimum daytime man
made noise at my location (0.40 microvolts per meter field strength measured as described above.

Hi guys

This is a collection of paper I was able to put together, please it is a working in progress and new entries are welcome. My eye is not doing well and it is hard for me to type, so this is a copy and paste.


March 5, 1919, Roy A. Weagant, Chief Engineer of the Marconi Wireless Telegraph Co. of America, delivered a paper describing in detail his apparatus for the elimination of the great bug-bear of transoceanic wireless communication --static interference. >>



Harold Beverage invented wide band receiver antenna, loaded loop. The present invention relates to short wave antennas and, more particularly, to antennas for receiving horizontally polarized waves over a wide band of frequencies. An object of the present invention is to enable the reception of horizontally polarized signals over a wide band of frequencies such-as is at present used in television.

https://docs.google.com/viewer?url=pate ... 247743.pdf


Nearly all the newly re-invented compact receive antennas derive from the terminated loop, the earliest reference was in an appallingly mimeographed prewar training manual of W3EEE Dad‘s


COMMUNICATIONS 74 CONFERENCE BRIGHTON Wednesday, June 5 1974 —Session 5 Equipment Design Paper 5.3: Loop Antennas for HF Reception Contributed by: B.S. Collins, C & S Antennas Ltd.,


JF1DMQ wrote an earlier article about the Flag antenna in November 1995 in a Japanese magazine. His was only 3.3 feet by 16.4 feet long (1 by 5 m). K6SE's 160m optimized versions are 14 by 29 feet (4.3 by 8.8m).


"Is This EWE for You?" (QST February, 1995, p.31) and "More EWES for You",
QST January, 1996, p. 32) both by WA2WVL.


The Pennant was originated by EA3VYand optimized for 160 meters by K6SE, who first wrote about them on the Top Band Reflector in 1998


The K9AYTerminated Loop—A Compact, Directional Receiving Antenna By Gary Breed, K9AY


W7IUV rotatable Flag and preamplifier >> http://w7iuv.com/


QST Magazine, July 2000, page 34 for K6SE's classic article:
"Flags, Pennants, and Other Ground-Independent Low-Band Receiving Antennas" ...


NX4D developed the first dual flag vertical array


N4IS developed the BIG flag vertical array


N4IS developed the Horizontal flag array


Dr Dallas Lankford, wrote the Flag Theory and design the Quad Flag Array >> Dallas Files The Dallas Files are now found here: http://groups.yahoo.com/group/thedallasfiles2


AA7JV George Wallner developed the DHDL (TX3A) >> http://tx3a.com/docs/TX3A_DOUBLE_HALF_DELTA_LOOP.ZIP


DOUBLING the Double Half-Delta Loop Receiving Antenna
by Pierluigi“Luis” MansuttiIV3PRK >>


Please add new papers



Thanks for posting this.

That first link doesn't work, it comes up article not found. The W7IUV link is down also.

The Dallas Lankford files have been removed (by request) and that Yahoo link is not valid any longer, but there are complete sets of his papers floating around on the Internet still.

Just wanted to mention that.

Rick Kunath, K9AO

Here the procedure I used to measure my receiver equivalent bandwith to
calculate NF.

https://www.owenduffy.net/measurement/e ... reIfBw.htm

SpecrunLab is also a very good tool to measure EBW

https://www.owenduffy.net/measurement/e ... eIfBw2.htm


http://www.contesting.com/_topband - Topband Reflector

73 Boye
Indlæg: 999
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Re: RX ant low band

Indlæg af oz7c »

Her er næste afsnit !
Det er N4IS der har meget erfaring med denne ant type
Her er en link til hans web page


Her er det sidste

Hi Guys

This concept is important and very confusing, so sorry for being a broken
record. I’ll keep it very simple to understand.

The Flag antenna and its variances, EWE, pennant WF SAL DHL and others
nice names are basic the same and like this:

Two wires in U shape, one upside down and one normal , with two openings.

| |

| |

| |

Open1 open 2

| |

| |

| |


The way to see it is like two vertical dipoles and two horizontal phasing
lines. On the opening one we terminate with a RESISTOR, the valuer of the
resistor is not important but for this exercise lets use 1000 ohms. Or two
vertical vectors and two horizontal vectors.

O the opening one we will connect the feed line. That’s the Flag, two
vertical in phase, Because the vertical dipole is too small it reflects the
current to the other dipole., and vice versa. The side one with the resistor
the current will be dissipated on the resistor,, but on the open 2 the
current can me connected to the feed line.

At this point the system could be balanced and the reactive component will
be very low if we pick for the feed line the same impedance of the load,
1000 ohms. You can simulate that on EZNEC and you will find it very

The 1000 ohms feed line is part or the receiving system and not part of the
antenna, so any loss will represent “noise” and will be add to the noise
figure of the receiver,. It you use a 9:1 transformer, the feed line could
be close to 100 ohm, It is simple to use a twisted pair close to 100 ohm
impedance , like twisted pair form a Ethernet cable will provide very low
SWR and no common mode noise, no shield is necessary.

The losses on the transformer and the feed like is part of the receiver
input circuit and not part of the antenna. The power noise is independent of
the valor of the resistor and the noise temperature on the vertical dipole
“open 2” is the same as any dipole. Please keep it simple and G/T of a
dipole is very well know. It is just two phased very small dipoles.

Based on the above is very simple to understand the EWE, just replace the
normal U by the antenna reflected by the ground (like a mirror). Cut all by
½, so the resistor will be 500 ohms and the impedance easy to match 50 ohms
using a 9:1 BALUN

Also the K9AY is easy to understand, just think the ground as a 1000 ohms
transmission line, and you can move the resistor close to the BALUN, like
the EWE.

As any antenna, the thermal noise is the limit of the amplifier to produce
any gain, if you want to work over 300 DXCC ( confirmed ) on 160m, make the
flag 24”x 12” and use it, spend time on that chair , tunning the radio and
enjoying 160, it is not easy and that’s why we love it.


I would like to share some of my experience with small flags'.

The directivity is the same for a large chance in frequency but the gain increase with size.

As a reference NX4D started with a single flag 14' high 7' wide , using a 20 db gain preamp. Is was good enough to work 150

countries on 160m, for 80m you can reduce the size by 1/2 and expect the same results. Basically it is a flag like k9AY, EWE, pennant and others

loaded loop, one resistor and one transformer.

The RDF is a limitation and Doug phased two loops 14x7 spaced 16ft for a

total boom of 30FT. all fiberglass, and an isolated mast from the tower and,

not portable, I called small Waller Flag. The two 14x7 flag was good enough

to work over 200 countries from a 1/5 acre lot in a subdivision with a lot of

noise form neighbors. Detuning the TX antenna was a must for good

performance, including working JT1CO direct path over the North pole on


But the gain of the antenna was a limitation on 160m, and he built a Monster

WF to work 311 DXCC on 160.

2 db NF and 20 db gain is all you need for a vertical flag or dual flag like the WF(Waller Flag, from Doug Waller, NX4D)

33db gain is too much for a flag or WF vertical, it is good for a flag or a

WF horizontal, and at least 75 ft above ground.

Here is important to remember if you S meter is moving you have too much
gain, I match my preamp gain for s0 on band noise during the day. There is a
lot of signals bellow S0. Keep the gain at minimum.

To reduce common mode noise a twisted pair 100ohms feed like helps a lot.

Measure noise figure at 1.8 MHz is a great task and care, with a good signal

generator and good sound card, you can take one measure in 2 hours of work

for -+ 0.1 db accuracy.

Doug me and Dr Dallas did a long experiment to measure that and a small flag

14'x7', was not thermal noise limited for DX use on low babnds.

At a very quiet rural area with -125 dbm noise floor during the day. For
reference , my city lot average -85 dbm during the day and the best I ever
measured was -95db on those winter Sunday Mornings with light rain.

The Dallas files is not available, Dr Dallas is SK but I have some paper I
can share here.

So a small loop is not thermal noise limited on 160m, and works very well on

80, 60 40 and 30m. some big contest station using a HWF reported problems of
power line noise on 20m and the HWF saved them transmitting on the yagis and
receiving on the HWF. On 80 and 40m the HWF is comparable only to a 4
elements full size yagi. ( same directivity, but vertical noise canceling)

The easy way and accurate is to use FSM easy to do in 3 steps , here >>>


FSM (for Field Strength Meter) is a software application that extends a
conventional SSB receiver to allow measurement and calculation of field
strength of radio signals or interference. FSM is a software implementation
of a development of the technique described by Ed Hare of the ARRL in
"Manual Testing of Field-Strength Levels Using Conventional Receivers" dated
August 2004 .

You need a good sound car and a 50 ohm shielded load, like an N or BNC
connector 50 ohm termination.


73 Boye
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Tilmeldt: søn feb 04, 2018 2:30

Re: RX ant low band

Indlæg af oz7c »

Indlæg: 999
Tilmeldt: søn feb 04, 2018 2:30

Re: RX ant low band

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I should have said the so the 4.5 dB noise figure is certainly not

Sorry for the typo.
Don (wd8dsb)

On Tue, Mar 9, 2021 at 6:20 PM Don Kirk <[email protected]> wrote:

> A couple of weeks ago there were a lot of postings about my portable flag
> for radio direction finding (for tracking down RFI), and someone asked
> about the DX Engineering preamp that was designed for use with my portable
> flag and specifically what the noise figure was for this preamp. Tim
> (K3LR) said DX Engineering would measure it, and today he reported it
> measured 4.5 dB.
> Tim mentioned that there were trade offs in the design such as low current
> draw and high gain, so the 4.5 dB noise figure is certainly unreasonable.
> It really is the only preamp I now use with my portable flag, and very
> pleased with how it works.
> Just FYI,
> Don (wd8dsb)
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

Ja det er nok ikke en preamp der vil noget, jeg syndes at kan huske N4IS preamp med nf 0.5 dB

73 Boye
Indlæg: 999
Tilmeldt: søn feb 04, 2018 2:30

Re: RX ant low band

Indlæg af oz7c »

et indlæg til om RX Ant.

Due to the many inquiries about the HIZ receiving antenna, I have created a description of how this antenna is constructed with the components.Have fun buildingthis effective antenna.
"DL8LAS DR5X Andree Schanko skimmer" https://www.dl8las.com/7m-hiz-antena-construction

73 Andy DL8LAS

Searchable Archives: http://www.contesting.com/_topband - Topband Reflector

73 Boye