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The Burhans bifilar winding? is an unusual winding method that produces a well balanced grounded centre tap winding which is resonated by a floating capacitor.? The capacitance of figure eight twin wire is very high so the inter turn capacitance is much higher than for a single winding, instead of the capacitance acting between turns the capacitance is between turns a long way apart.? This is the same problem as bundling turns together in a multi-turn loop or using rainbow wire or multi-core cable, the distributed capacitance results in a Q very much lower than expected and so reduces sensitivity in the same proportion.

In the Loran? application you don't want high Q at all, the signal is a short pulse of energy that spans a broad bandwidth so a Q of around? 5 would be around the maximum for the application. But in most general receiving applications a Q of 100 or more is desirable to get the 20x improvement in signal level.

There are some oddities in the Burhans paper. One unique feature of Loran ( and other Pulse nav systems ) is that the polarity of the received signal is important, normally E-Field antennas were used so the polarity is as received but with a loop antenna the polarity depends on which half of the polar diagram the signal is coming from. At 100KHz this could lead to a 1,500m positional error.? There is also the issue of directivity, what happens in a single rod antenna when you fly into the null.? Burhans? idea of summing several rods at various angles just does not work.? You need to know which direction the signals are coming from, a single rod? might be? correct for one transmitter but anti-phase for others and null? out fairly frequently on one or more signals.

H field antennas were used in the latter days of Loran ? however? they were designed when processors could do things not possible when Burhans wrote his paper.

I don't think that the bifilar winding method is of value in general applications, it needs a floating tuning capacitor ( a dual varicap would work) but suffers from the high capacitance between windings which would greatly restrict tuning range. The Polydoroff winding? method of two separate windings on each half of the rod with one winding reverse wound is a much better solution, the windings are grounded at the outsides and the middle point output is in the best location? for a screening viewpoint.

73, Alan G8LCO

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Here is an article I wrote a few years ago, that is in the files section of this group. It discusses several different winding configurations, including contra.?

Look at the article in June 1983 Radio Electronics magazine page 83 Loop antennas for VLF-LF for ideas on winding antenna coils.


John KK6IL@...

G’day all,
I just filled a 6 x 3/8 inch ferrite rod with small figure 8 wire and got about 340uH of inductance for the bifilar winding.
Works well as an external antenna on my Tecsun PL365 with SI4735 for MF and LF.
Just need to get some Al channel stock for the electric shield.
Andrew VK5CV

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I tried a bifilar winding on a tuned loop once and it wasn't very successful. I wound the loop with twin bell-wire and wound half the number of turns required for a single wire and then connected the finish of the first wire back to the second wire at the start of the winding. The inductance measured OK but was a "dud" as an antenna. Splitting the conductors and winding conventionally fixed the problem. Bifilar windings work well with wideband transformers e.g toroids and binocular ferrites but I have my doubts about ferrite rods and loops.

Regards, Ian Brooks, Verwood, Dorset, UK.

Note that since this is a tuned loop, it's important to keep additional capacitance placed across the tuned circuit as low as possible. Excess C will lower the highest frequency tunable with any particular loop coil, although with the MF coil spec'ed for 530 to 1900 kHz, lowering the 1900 a little won't hurt.

John

On Thu, Feb 3, 2022 at 10:56 AM, Jeff Green wrote:

https://www.radiomuseum.org/r/mckaydymek_amplified_loop_base_system_da_9.html

Tuned loops require a Hi-Z buffer, if the coupling is a direct connection (no coupling coil). Loop inductance + tuning capacitor form a high impedance source, unlike the broadband untuned loop, which is a low impedance source.
PA0RDT buffer should work just fine in this application.

73, Mike AF7KR

It helps when posting links that you write a brief description.

Blame spammers and scammers. They are what make us all paranoid about clicking links.

Steve

I only answered Tom Seeger's question: "Do you have a link to "the new Wellgood V3 PCB" boards?"
?

--

Unless I or another moderator here tells you to stop, I'd treat an off-list complaint as a troll.


--
Steve Greenfield AE7HD

Has anyone tested connecteing youloop on a MLA 30 amplifier?
Thanks

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Like Alan , I have a fixed loop in the roof-space. In my case it was a home-brewed Moebius loop, the same size as the commercial YouLoop. I already had a larger one going around a window-frame, which favoured North-South reception. I wanted to align the loft-mounted one for North American MW reception and had found that a BBC Local Radio transmitter in North Devon (West of England) was almost exactly on the correct bearing for this. I took my Degen DE1103 into the loft and found the "null" for this station to give me the direction for my loop. A bradawl, some string and some cup-hooks completed the job. Unfortunately the BBC transmitter that I used has since closed down. The loop now enables reception of the "easier" US stations with my Airspy HF+ SDR. Previously I had used the Degen, either on its own or with a small Tecsun AN100 loop.

Ian Brooks, Verwood, Dorset UK (10 miles north of Bournemouth.)

I have a loop in the loft space so to get a good idea of the direction it was pointing, I used Google Maps to show my house, used the 'measure distance' function to draw a line along the front face of my house, extending this line in both directions (the longer the better) then right-click on the endpoints to get the lat and long coordinates of both ends. It's then simple to calculate the bearing of that line and hence the front of your house - there are websites that will calculate this for you, but I can't remember which I used. I then drew that bearing on the ns6t map centred on the coordinates on my house. I did this for a local (UK) map, a Europe map and a world map.

That gives me a good indication of where the loop is pointing and will do until I can build a rotator!

On Wed, Feb 2, 2022 at 01:17 AM, Tom Seeger wrote:

I rotate it until I get minimum local noise pickup.

I agree, the maximum signal response of loops is fairly broad, whereas the nulls are usually very sharp, so it's often more useful to reduce the level of unwanted noise and interfering signals, rather than trying to obtain the strongest signal from the wanted station.

Regards,

Martin

I rotate it until I get minimum local noise pickup. In my case that's the only advantage my loops have had (and only on certain bands) over an omnidirectional antenna like my vertical active dipole, active whip and broadband vertical.
Once that's done, it just stays there. It is nice to know which way the null is though, and for that I use a compass and google maps.
73 Tom