Re: Pixel Technologies RF PRO-1A Shielded Loop vs Wellbook ALA1530
- I'm interested in knowing if anyone has done testing between the mobius and any other loops comparing numeric S/N or NF or 'transient' E-field "noise reduction". Would like to see the test data.
--- In email@example.com, "lexluthor6969" <lexluthor6969@...> wrote:
> I have been using the new Pixel Technologies RF PRO-1A loop .
> And also running side by side tests comparing it to the latest version
> of the Wellbrook ALA1530
> Both antennas are somewhat similar in size and price.
> - The Pixel antenna is made in the US, while the Wellbrook is made in
> - I believe both antennas have 30 db (approximately) low- noise preamps
> that cover up to 30 MHz
> - Both are broadband "receive-only" antennas that require no tuning
> - I believe both have noise-figures in the 2 -3 dB range
> - The Pixel antenna has substantially better IMD specs (OIP2 > 100dB,
> OIP3=48dB) vs the Wellbrook (OIP2 = 80dBm, OIP3 = 43 dBm). This is
> significant in locations where there are strong AM broadcast band
> signals and other high power signals present that might overload the
> - Both amps have internal low - pass filters that knock out local high
> power TV and FM stations above 30 MHz that could overload the amp
> - The Pixel loop is a shielded 2-turn (effective) Moebius configuration
> (similar to the antenna Chris Trask has described elsewhere) while the
> Wellbrook is a traditional unshielded single-turn configuration. The
> Pixel and Trask antennas are based on the work of Dr. Carl Baum who
> developed this architecture for a classified US Air Force project.
> - Both are about 1 meter in diameter
> - Both use 3/4 inch aluminum tubing construction.
> - The Pixel antenna is anodized a satin gray color to prevent
> corrosion. The Wellbrook is natural aluminum not anodized
> - The Pixel antenna weights a little more since it has a center support
> brace that provides more support for the Moebius junction box .
> - The Pixel antenna is provided with a standard L-bracket, U- bolts and
> saddle clamps to mount it to a flat surface or any pole up to 2 inches
> in diameter, while the Wellbrook does not include these items and
> it's up to the user to improvise mounting
> - Both can be used at ground level to provide good reception. In my
> setup I have them mounted about 6 feet off the ground on rotors.
> - No special grounding for good signal reception is required for either
> antenna, although the Pixel antenna has a large lug to attach a
> grounding wire to provide standard lightening protection.
> - Both antennas include a power supply and power inserter that duplexes
> power and signal onto one cable lead that goes to the antenna and preamp
> - The Wellbrook uses standard BNC connectors on the antenna which must
> be weather- proofed while the Pixel uses water proof F-connectors
> that are provided
> - The Pixel is designed to work with standard low- cost RG-6 75 ohm
> cable (the same as that used with satellite TV dishes). There is an
> impedance matching device and PL-259 adapter to mate with standard 50
> ohm input Z radios. Wellbrook recommends RG-58 50 ohm cable that must
> be fitted with BNC plugs.
> - The low- noise amplifier in the Wellbrook is encapsulated in tamper
> proof epoxy in an unshielded plastic enclosure that is attached to
> the aluminum loop structure. There is no easy way to remove it from the
> loop or get access to the interface between the loop and the amp to
> insert, for example, a broadcast AM radio band elimination filter in
> certain circumstances. This configuration makes the amp very difficult
> to repair or replace. I'm not sure how Wellbrook deals with this,
> but sending the entire 1 meter antenna to England for repair has got to
> be an expensive time-consuming process. On the other hand, the Pixel
> amplifier is a separate assembly that is mounted inside a metal shielded
> enclosure that attaches to the loop antenna through a short cable that
> is easy to access to add input filters or remove for repair or
> - Pixel at present only sells this in a North American version while
> the Wellbrook is available with power supplies for Japan, Europe and
> North America. Both companies provide highly filtered specially designed
> low- noise linear power supplies. The Pixel has an internal self-
> reseting fuse to protect the supply in case of an inadvertent short or
> over current condition while the Wellbrook has a standard user-
> replaceable slow-blow fuse for protection. The Pixel has a high voltage
> discharge- tube for lightening protection on the lead in wire from the
> amplifier. I'm not sure if the Wellbrook provides any special
> protection for induced high-voltage transients on its lead in wire.
> - The Pixel antenna includes an internal Transmit /Receive switch that
> permit the user to optionally connect it to a transceiver's
> "KEY" output to automatically remove preamp power and also
> disconnect it from the receiver when you are transmitting. A handy
> feature if you are mounting the loop in the vicinity of a transmitting
> antenna. With the Wellbrook, you need to purchase a T/R switch
> separately or place the antenna at least 80 feet away from the transmit
> antenna. The Wellbrook's amplifier when it is saturated outputs
> nearly 1 watt into your receiver which could cause damage in some
> receivers, so some considerable care should be taken when using this
> antenna in conjunction with a transmitter. Since the amplifier has
> nearly 30 dB gain, it does not take much power coupled from a transmit
> antenna to saturate it.
> - I'm using these antennas with a software defined- radio (SDR)
> that allows me to view and receive the entire 30 MHz spectrum at one
> time. These kind of broadband loops are a perfect match for SDR's
> since no narrow- band Hi-Q antenna tuning is utilized.
> - From the standpoint of performance, definitive side- by- side tests of
> the two antennas is still a work in progress but my initial reactions
> are that the Pixel antenna has the edge especially at frequencies below
> 10 MHz where the Moebius loop provides a very noticeable improvement in
> received S/N. More definitive quantitative results will be provided in a
> future post.
> - Both antennas exhibited very impressive and significant rejection of
> local near-field QRM and mains/power line radiated noise as compared to
> common E-field electric antennas. I'd say they were both equal in
> this regard. Both had the classic "figure eight" reception
> pattern with very sharp 30 dB nulls at right angles to the plane of the
> - Andy Ikin from Wellbrook has posted results of side by side tests
> taken at a test facility of a Moebius antenna he made compared to his
> improved ALA1530. He used a magnetic signal source in near-field
> conditions. From these tests he concludes that the Moebius is vastly
> inferior above 18 MHz. However I have not been able to observe these
> results with reception of real-world far field signals. The tests
> he did only considered near- field reception of H-field magnetic
> signals. Both kinds of loops have significant E-field response as well
> as H-field response to far field-signals. It's possible that the
> increased loop area (a factor of 6 dB) of the Moebius loop provides
> superior E-field response that compensates for the lower H-field
> magnetic response he observed. The jury is still out on exactly how the
> physics of all this works since the Moebius loop is new to the shortwave
> community. But so far this evaluation, Chris Trask's results and the
> observation of others that have built these new Moebius loops seem to
> confirm the superiority of the Moebius shielded loop architecture. More
> [Non-text portions of this message have been removed]
- you need to look closely at the M=2 Baum Moebius device as the M=1 is not really
effective at noise reduction IMHO
you need to read the original Dr Carl Baum notes on the higher order Moebius
antenna devices he developed and used
best Paul VE3PVB
I'm interested in knowing if anyone has done testing between the mobius and any
other loops comparing numeric S/N or NF or 'transient' E-field "noise
reduction". Would like to see the test data.
[Non-text portions of this message have been removed]
- Hi Paul,
Thanks for your info. I think I'm missing something. I've read Baum's paper several times, but don't see a reference to the M=2 viz M=1 reference in his paper. Can you point me to what I'm not seeing? The Baum paper I reviewed is "Characteristics of the Moebius Strip Loop" Regards,
--- In firstname.lastname@example.org, Paul V Birke PEng <nonlinear@...> wrote:
> you need to look closely at the M=2 Baum Moebius device as the M=1 is not really
> effective at noise reduction IMHO
> you need to read the original Dr Carl Baum notes on the higher order Moebius
> antenna devices he developed and used
> best Paul VE3PVB
> I'm interested in knowing if anyone has done testing between the mobius and any
> other loops comparing numeric S/N or NF or 'transient' E-field "noise
> reduction". Would like to see the test data.
> [Non-text portions of this message have been removed]
- A bit dated - but I thought my recent purchase and experience might be of some importance.
My experience with loops goes back to the mid 60's when I experimented with 7" non-descript ferrite rods from Lafayette Radio - and, eventually, TI TIS-34 jFETs. I have built large & small box loops - even remotely tuned. My experience with broadbanded low-Z loops is rather limited. My biggest awakening has been on parts acquisition - CATV transistors seem all but impossible to find these days. I took the simple way out - I spent money - and bought 'someone else's loop'. I considered the Wellbrook - until I heard about the modular Pixel Technolgies RF Pro-1a. Made in USA - like my last receiver - a Palstar R30A was a plus, too.
I tried it in my shack - and it could null some noise sources. I mounted it on a 5ft mast - in turn, I mounted the mast with a wall bracket to the end 2" x 8" plate on my deck, maybe 2 ft off the ground. With the loop parallel to the house - internal noise sources are effectively nulled. Only a faint hint of the aperiodic coronal discharge from a power pole is heard - <S1 in the few empty areas 10-18 MHz I tried. Atmospherics, signals, etc, overshadow the coronal discharge at lower frequencies - early afternoon - evening.
In my case, this loop is a winner - just what I needed. It covers LW quite well - I have never heard even the local 'BH' aeronautical beacon on 224 kHz so clean. Sure, it was a few bucks - you'll have most of half a kilobuck in the antenna and it's installation. Don't skimp on RG-6 - get the good stuff - quad shield - and a crimper for the waterproof connectors, too. DOn't forget a ground rod - recycling old coax (RG-8/11) makes a great ground wire - parallel the inner & outer connections. I am happy!
- I am a recent owner of the Pixel loop too. My impressions are mixed between excited and disappointed.
I am excited because the thing actually works, and seems to work well. Signal strength is not as good as my 180 foot wire on higher frequencies, but on lower frequencies it does well on siganl strength. The main thing is the noise is gone. All the power line "buzzzzz" is history - which makes for a nice signal to noise and clean readable signals.
What is disappointing is the build. The loop itself is parts from home depot mostly. That in its self is not a problem, because things can be replaced locally and inexpensively. It is how it is put together that is bothersome.
The shielded portion of the loop is aluminum tubing. It is attached at the bottom by pop rivets. This is an electrical connection as well as a mechanical one. The wire inside the loop is very small gauge, about 18 or 20 gauge by the look of it... maybe even as small as 22. What is clear about this design, is they did not do much to minimize resistance like you would in a transmitting loop. There is a heavy reliance on the loops ability to reject noise, and the preamplifier to boost the signal. I wonder how well this loop will work when exposed to weather for some time, and these connections become loose and weathered.
As it is, I feel compelled to rebuild parts of the loop. Increase the wire size to about 6 or 4 gauge, and a more reliable electrical connection at the bottom of the loop.
- I saw one of these at the Orlando hamfest a couple of weeks ago, but
didn't think to check to see if it could be weatherproofed better. Do
you think it be possible to weather-seal the bottom joints with some
large heat-shrinkable tubing?
At 09:04 PM 2/28/2011, you wrote:
>I am a recent owner of the Pixel loop too. My impressions are mixed
>between excited and disappointed.
>I am excited because the thing actually works, and seems to work
>well. Signal strength is not as good as my 180 foot wire on higher
>frequencies, but on lower frequencies it does well on siganl
>strength. The main thing is the noise is gone. All the power line
>"buzzzzz" is history - which makes for a nice signal to noise and
>clean readable signals.
>What is disappointing is the build. The loop itself is parts from
>home depot mostly. That in its self is not a problem, because
>things can be replaced locally and inexpensively. It is how it is
>put together that is bothersome.
>The shielded portion of the loop is aluminum tubing. It is attached
>at the bottom by pop rivets. This is an electrical connection as
>well as a mechanical one. The wire inside the loop is very small
>gauge, about 18 or 20 gauge by the look of it... maybe even as small
>as 22. What is clear about this design, is they did not do much to
>minimize resistance like you would in a transmitting loop. There is
>a heavy reliance on the loops ability to reject noise, and the
>preamplifier to boost the signal. I wonder how well this loop will
>work when exposed to weather for some time, and these connections
>become loose and weathered.
>As it is, I feel compelled to rebuild parts of the loop. Increase
>the wire size to about 6 or 4 gauge, and a more reliable electrical
>connection at the bottom of the loop.
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