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But what worries me, the very thin coaxial inner conductor is in
series with the main loop conductor. It may have a loss resistance several times greater than the large diameter main loop. You could be losing a lot of decibels. ===================================== Lee, If you cut the length of coax into, say, 7 equal lengths and connected them in parallel you will have a capacitor of the same value but with a loss resistance only 1/7th of the single length. More compact too. 6 fit very nicely round 1. Bundle them up in a plastic bag to keep off the rain. ---- Reg, G4FGQ. |
"Reg Edwards" wrote in message ... Lee, Using the loop indoors, at ground-floor level, at 20MHz, on a groundwave path, is not inconsistent with what you get. Get it high-up, outdoors, and it will make a big difference. Next, after testing 2` above ground....... The capacitor is made from a length of coax. I wonder how long it is and how it is located relative to the loop? Wherever it is, being unbalanced coax it will unbalance the loop. Isn`t a variable butterfly vane capacitor unbalanced also as is the co-axial trimpot and the compression piston cap?..they are all used on magloops Reg. But what worries me, the very thin coaxial inner conductor is in series with the main loop conductor. It may have a loss resistance several times greater than the large diameter main loop. You could be losing a lot of decibels. I`m listening Lee....G6ZSG..... |
"Reg Edwards" wrote in message ... Lee, If you cut the length of coax into, say, 7 equal lengths and connected them in parallel you will have a capacitor of the same value but with a loss resistance only 1/7th of the single length. RG8 / UR213 would be more convenient i should think Reg if i were running a bit more QRO...... More compact too. 6 fit very nicely round 1. Bundle them up in a plastic bag to keep off the rain. I`ll try that Reg..... i have an old QRP atu with air spaced variables around 350pf with slow motion drive i could use on a more ambitious project a little later....good for 100watts or so SSB...Yes? Lee...G6ZSG....... |
The intermod performance of a receiving pre-amplifier is of no
consequence with a magloop. The Q and selectivity (of the order of 1000) of the loop at the wanted frequency easily reject local high-power MF broadcast frequencies. On 160m, It's difficult to hear any stations only 3 kHz away from the wanted frequency. ---- Reg. |
"Reg Edwards" wrote in message ... The intermod performance of a receiving pre-amplifier is of no consequence with a magloop. The Q and selectivity (of the order of 1000) of the loop at the wanted frequency easily reject local high-power MF broadcast frequencies. On 160m, It's difficult to hear any stations only 3 kHz away from the wanted frequency. ---- Reg. Hi Reg.... I took my little 1 meter dia ( 10 ft circ ) loop outside lunchtime and mounted it verticaly 2ft off the lawn and tested it, not expecting anything special and found that comparing it to the G5RV that there was no noticable difference between the two!!...my friend and i switched out our preamps and attenuator in. I even turned the loop face on and edge on with a change of 2-3 S points.. So, needless to say, i am rather impressed with the performance and bandwidth of 2:1 SWR about 180k.....so much so that i am thinking seriously of going for a 20 ft circumference or larger for 80 and 40 metres.... Regards. Lee....G6ZSG.....Well impressed!!! :-) |
Dear Reg (G4FGQ):
I note with interest that your note was written in the early afternoon. The subject of my communication is: small (much smaller than a wavelength) - non-resonant (input impedance almost entirely inductive if one looks into a single opening in the loop) - horizontal - loop antenna (no substances with significant magnetic properties are in the vicinity of the loop antenna) - used to receive incident EM waves (which have both E and H components). SNRHL receiving antennas I do not know the definition of a "magloop." Apparently, such a beastie comprises a resonant loop antenna. No knowledgeable person would disagree that a single tuned network with a Q of 1000 is "narrow." My interest in SNRHL receiving antennas comes from an interest in practical HF receiving antennas that are resistive to types of noise that appear only to be present at isolated, open, rural, otherwise-low-noise sites. The noise involved does not occur in urban areas or even rural sites with many trees. Consider some of the excellent wine from Michigan this evening. This state, with a coastline almost the same length as that of the island of Great Britain, produces some excellent products for your enjoyment. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Reg Edwards" wrote in message ... The intermod performance of a receiving pre-amplifier is of no consequence with a magloop. The Q and selectivity (of the order of 1000) of the loop at the wanted frequency easily reject local high-power MF broadcast frequencies. On 160m, It's difficult to hear any stations only 3 kHz away from the wanted frequency. ---- Reg. |
Hello Lee,
Thanks for letting me know that by giving your magloop half-a-chance it performs according to expectations. You have also demonstrated that the G5RV is not so hot as it is made out to be by salesmen and they who have never tried anything else. No disrespect intended to G5RV himself, now deceased, who claimed only that it had a nice radiation pattern on 14.15 MHz which enabled him to work both Europe and North America from South America without having to climb ladders and change anything. The magloop is by far the most efficient of all the antennas of roughly the same physical size. Both theoretically and in practice. It will do even better if you can get it well above ground in the vertical plane. In the horizontal plane it works best at the higher heights, above surrounding obstructions like buildings. But in such surroundings there is room to erect full-size dipoles anyway, which will obviously do better still. The main disadvantage on the 160 and 80 meter bands is the size, physical and capacitance-wise, of the variable tuning capacitor. You need a vaccuum capacitor of about 1000 pF max. By correct choice of loop dimensions and minimum capacitor setting the 40 meter band can also be covered. On 40 meters a small magloop can be highly efficient. Investigate using program MAGLOOP4. Are you using the small internal coupling loop, about 1/5 diameter of main loop, to match to a 50-ohm feedline? This is the best and most simple way to go, A different ratio small loop diameter is needed for other feedline impedances. The circuit behaves as if the turns ratio on a transformer is being changed. Let us know how your experiments proceed. ---- Reg, G4FGQ. |
"J. Mc Laughlin" wrote Dear Reg (G4FGQ): I note with interest that your note was written in the early afternoon. ========================================== My Dear J. Mc Laughlin, Thank you for your interest in my early afternoon state of health. It is now 19.15 hours and I have just started on a bottle of Sierra Valley, Californian, Ruby Cabernet. The subject of my communication is: small (much smaller than a wavelength) - non-resonant (input impedance almost entirely inductive if one looks into a single opening in the loop) - horizontal - loop antenna (no substances with significant magnetic properties are in the vicinity of the loop antenna) - used to receive incident EM waves (which have both E and H components). SNRHL receiving antennas I do not know the definition of a "magloop." Apparently, such a beastie comprises a resonant loop antenna. ======================================= "Magloop" describes a small, single-turn, thick conductor, usually made from copper water pipe, circular, hexagonal or square in shape, loop. The two ends of the loop are connected together via a variable capacitor. The capacitor tunes the inductance of the loop to a resonant frequency at which everything happens. The term "magnetic" arises because the near-field of a transmitting loop is mainly magnetic as distinct from the electric field. On receive it is more sensitive the magnetic field than the electric field. ======================================= No knowledgeable person would disagree that a single tuned network with a Q of 1000 is "narrow." My interest in SNRHL receiving antennas comes from an interest in practical HF receiving antennas that are resistive to types of noise that appear only to be present at isolated, open, rural, otherwise-low-noise sites. The noise involved does not occur in urban areas or even rural sites with many trees. ===================================== The noise in rural, open, oceanic areas is just the same sort as in built-up, residential, city and industrial areas. It is all random but there is just a lot less of it. An antenna of any sort is just as sensitive to noise as it is to signals provided both noise and signals are coming from the same direction and elevation. ====================================== Consider some of the excellent wine from Michigan this evening. This state, with a coastline almost the same length as that of the island of Great Britain, produces some excellent products for your enjoyment. ======================================= Everybody has heard of the State of Michigan with its capital city of Detroit. I have always thought of it as an industrial state similar to my own area of the city of Birmingham and the surrounding Black Country of England. It is the manufacuring areas which produce the REAL wealth of this World of ours. Not forgetting the farmers. Never having had the opportunity to visit Michigan it has not occurred to me that the land could also grow grapes and produce wine. (Actually, we do produce respectable wine here in cool-climate industrial England. But not much of it.) It is now 20.00 hrs and too late to go shopping at my local super-market. Nevertherless, at my next visit I shall keep my eyes open for "Michigan" on the wine bottle labels. ---- Reg, G4FGQ. |
Hi Lee,
I'm a little confused about the bandwidth that you're getting. Maybe it can be attributed to losses which widen the SWR bandwidth. That's not necessarily a bad thing. I have used an AEA IsoLoop antenna that is about the same size as your loop antenna but has a low loss butterfly capacitor for tuning 10-30 MHz. On 20 meters the bandwidth is only about 20 or 30KHz(can't remember exactly since I haven't used it for a couple of years). It works great if you park yourself on a frequency but it is a pain to use for hunt and pounce. Besides the null using vertical polarization, is it possible that for your local friend you may have been cross-polarized. Usually direct wave cross-polarization is on the order 20db which accounts for the 2 to 3 S units of change from vertical to horizontal. Have fun with your new toy! 73 LT Hi Reg.... I took my little 1 meter dia ( 10 ft circ ) loop outside lunchtime and mounted it verticaly 2ft off the lawn and tested it, not expecting anything special and found that comparing it to the G5RV that there was no noticable difference between the two!!...my friend and i switched out our preamps and attenuator in. I even turned the loop face on and edge on with a change of 2-3 S points.. So, needless to say, i am rather impressed with the performance and bandwidth of 2:1 SWR about 180k.....so much so that i am thinking seriously of going for a 20 ft circumference or larger for 80 and 40 metres.... Regards. Lee....G6ZSG.....Well impressed!!! :-) |
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