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Locked Flat Spirals

 

There's been some interest in flat spiral antennas for HF recently, see:
Harry, SM0VPO - http://sm0vpo.altervista.org/antennas/frameant.htm
Frank, N4SPP - https://www.nonstopsystems.com/radio/frank_radio_antenna_SM0VPO.htm#top-of-page
Mike, M0MSN - https://www.youtube.com/c/hollyend01/videos
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How efficient are these compared with the more conventional magnetic loops?
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Are they better relegated to being receive only active antennas?
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Thanks,
?
Keith? M0KIL.
 

On Mon, Apr 25, 2022 at 10:57 AM, keith Lockstone wrote:
?
How efficient are these compared with the more conventional magnetic loops?
Generally speaking they are really only useful as LF and MF receive antennas.

Increasing the number of turns also increases the overall conductor length and consequent resistive losses per unit length.

For amateur use on the 160, 80 and 40m bands a two turn loop is about the optimum, and a single turn loop is better on the HF bands.

Try this on-line magnetic loop calculator to see for yourself.



You can vary the number of turns (up to 8) and the spacing between turns to observe how these changes affect other parameters.

The biggest problem with multi-turn loops is in supporting and keeping the wires stable relative to each other, as this can cause the SWR to vary excessively when transmitting.

Regards,

Martin
 

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I have been using spiral loops exclusively for reception of LW, MW, and SW many years.? I understand, despite their low radiation resistance, loops have become quite popular for transmission experimentation among hams in recent years.

The spiral geometry provides minimum distributed capacitance in a coil.? This leads to the possibility of a higher L/C ratio in a resonant circuit and greater sensitivity.? All my antennas are resonant primary circuits transformer coupled through a low-impedance coil and twisted pair to the receiver.? The secondary (coupling) loop must provide a good impedance match to the transmission line and have a suitable coefficient of coupling with the primary circuit.

My current articles in the files section are as follows:

PRTC Loop Antenna - 2022_02_14.pdf is a 3' diagonal spiral covering 2.6 to 12.1 MHz.

Electrically Small Resonant Loop for Shortwave (Oct '14).pdf is a 2' diagonal version covering approximately the same band of frequencies.

Electrically Small Resonant Loop Antenna for Mediumwave Reception.pdf is the current draft of my MW article, which identifies a lot of my engineering sources, theory, and construction details.

Hope some of this is helpful.

Bob C.
ED MONTAIGNE
 

Remember that flat spiral antennas are very wide band ant that means low Q which equals more QRM/QRN. Narrow band means High Q and low noise.


On Mon, Apr 25, 2022, 8:53 AM Dexter <dexterdxer@...> wrote:

I have been using spiral loops exclusively for reception of LW, MW, and SW many years.? I understand, despite their low radiation resistance, loops have become quite popular for transmission experimentation among hams in recent years.

The spiral geometry provides minimum distributed capacitance in a coil.? This leads to the possibility of a higher L/C ratio in a resonant circuit and greater sensitivity.? All my antennas are resonant primary circuits transformer coupled through a low-impedance coil and twisted pair to the receiver.? The secondary (coupling) loop must provide a good impedance match to the transmission line and have a suitable coefficient of coupling with the primary circuit.

My current articles in the files section are as follows:

PRTC Loop Antenna - 2022_02_14.pdf is a 3' diagonal spiral covering 2.6 to 12.1 MHz.

Electrically Small Resonant Loop for Shortwave (Oct '14).pdf is a 2' diagonal version covering approximately the same band of frequencies.

Electrically Small Resonant Loop Antenna for Mediumwave Reception.pdf is the current draft of my MW article, which identifies a lot of my engineering sources, theory, and construction details.

Hope some of this is helpful.

Bob C.
 

¿ªÔÆÌåÓý

My post refers to tuned (inductance-capacitance) circuits.? Properly constructed, a spiral loop will have a bandwidth (-6 db) of just a few kHz at lower SW frequencies.? The Q is extremely high, adjacent QRM and local noise significantly mitigated.

Bob C.

On 4/25/2022 6:04 PM, ED MONTAIGNE wrote:

Remember that flat spiral antennas are very wide band ant that means low Q which equals more QRM/QRN. Narrow band means High Q and low noise.

On Mon, Apr 25, 2022, 8:53 AM Dexter <dexterdxer@...> wrote:

I have been using spiral loops exclusively for reception of LW, MW, and SW many years.? I understand, despite their low radiation resistance, loops have become quite popular for transmission experimentation among hams in recent years.

The spiral geometry provides minimum distributed capacitance in a coil.? This leads to the possibility of a higher L/C ratio in a resonant circuit and greater sensitivity.? All my antennas are resonant primary circuits transformer coupled through a low-impedance coil and twisted pair to the receiver.? The secondary (coupling) loop must provide a good impedance match to the transmission line and have a suitable coefficient of coupling with the primary circuit.

My current articles in the files section are as follows:

PRTC Loop Antenna - 2022_02_14.pdf is a 3' diagonal spiral covering 2.6 to 12.1 MHz.

Electrically Small Resonant Loop for Shortwave (Oct '14).pdf is a 2' diagonal version covering approximately the same band of frequencies.

Electrically Small Resonant Loop Antenna for Mediumwave Reception.pdf is the current draft of my MW article, which identifies a lot of my engineering sources, theory, and construction details.

Hope some of this is helpful.

Bob C.
 

Not sure how well they perform but Tak Tenna has a beam version of flat spirals. They use the antenna frame to hold the windings in place as well as a reasonably stiff wire. I assume the last part as I have only seen pictures and ads of the antenna.

https://tak-tenna.com

in addition, there is an updated version of the Paraset Radio, the Bayou Jumper, from the 4 State QRP Group (4sqrp.com) that uses flat spiral coils for the inductors.

73,
kc6pob
On Monday, April 25, 2022, 05:53:48 AM PDT, Dexter <dexterdxer@...> wrote:


I have been using spiral loops exclusively for reception of LW, MW, and SW many years.? I understand, despite their low radiation resistance, loops have become quite popular for transmission experimentation among hams in recent years.

The spiral geometry provides minimum distributed capacitance in a coil.? This leads to the possibility of a higher L/C ratio in a resonant circuit and greater sensitivity.? All my antennas are resonant primary circuits transformer coupled through a low-impedance coil and twisted pair to the receiver.? The secondary (coupling) loop must provide a good impedance match to the transmission line and have a suitable coefficient of coupling with the primary circuit.

My current articles in the files section are as follows:

PRTC Loop Antenna - 2022_02_14.pdf is a 3' diagonal spiral covering 2.6 to 12.1 MHz.

Electrically Small Resonant Loop for Shortwave (Oct '14).pdf is a 2' diagonal version covering approximately the same band of frequencies.

Electrically Small Resonant Loop Antenna for Mediumwave Reception.pdf is the current draft of my MW article, which identifies a lot of my engineering sources, theory, and construction details.

Hope some of this is helpful.

Bob C.
 

On Mon, Apr 25, 2022 at 10:04 PM, ED MONTAIGNE wrote:
Remember that flat spiral antennas are very wide band ant that means low Q which equals more QRM/QRN. Narrow band means High Q and low noise.
Hi Ed & Bob,

A high Q antenna can act as a pre-selector / band pass filter, which may help prevent overload from other strong stations on nearby frequencies, but this is less of a problem than it used to be with modern receivers.

However, a High Q antenna can actually introduce more Noise and QRM within its passband,? as it is more likely to interact with nearby conductive objects than a low Q broadband loop. It is also more susceptible to common mode current and Noise conducted along the feed cable.

Providing steps are taken to maintain the loop balance and adequate feed line chokes are utilised, high Q tuned loops can work well, but it's probably best not to make assumptions about what is the best performer under various conditions.

Regards,

Martin
 

Another downside to high-Q antennas is the effect on waterfall displays.? They're OK for digimodes that operate in narrow bands but not helpful in SSB contests.

Keith? M0KIL.
 

That¡¯s not really true

I have no problems as long as on one band.. ie 160m. one still can see the activity perfectly well.. its just not linear across the display.

I have just 2.5khz useable bandwidth on 160m, just enough for tube amp to give full output without complaining.

Simon g0zen
 

And besides..who uses a magloop ( or other narrow bandwidth antenna) for rx in a competition? One uses active rx loops/ beverage/ short verticals etc ( on low bands) and then tunes mag loop to frequency of interest..

Simon

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