MFJ-1782 Loop Antenna?
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Has anyone tried, or using, a MFJ-1782 HF LOOP
Antenna - or homebrew of this? Some sites claim good HF success with this small circular loop HF antenna. I'm not a fan of MFJ's quality, by a long shot - but owners claim - with care, it works pretty well. What do you think? Is this a small stealth antenna that would work? Fred N3CSY __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
RE: MFJ-1782 Loop Antenna?
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Fred, N3CSY asked:
Has anyone tried, or using, a MFJ-1782 HF LOOP Antenna - or homebrew of this? Some sites claim good HF success with this small circular loop HF antenna. I'm not a fan of MFJ's quality, by a long shot - but owners claim - with care, it works pretty well. What do you think? Is this a small stealth antenna that would work? ------------------------------------------------------- They do "work" Fred, but they are very, very lossy antennas. That's not MFJ's fault, its inherent in the design. The problem is that the RF currents go up as the impedance goes down. Small loops are very, very low impedance antennas, so the currents are very, very high (wore out the "very" keys on my machine writing that...). That's why MFJ makes a big deal about no "mechanical" (meaning screwed or riveted) connections. Every milliohm of resistance counts in a big way. When we finally get room-temperature superconductors, small transmitting loops will take their place alongside many other high-efficiency design. In the meantime, they're about as good as most antennas their size. One of the big issues with a small loop is matching it to a 50 ohm output of a rig. It requires an impedance matching network capable of doing that, and almost no "normal" antenna tuner can do it. A big part of what you're buying with that loop is the tuner that can handle that very low impedance. That's why MFJ doesn't try to go below 10 MHz with their design. Like any antenna that is smaller than 1/2 wave long, the bigger you can get it the more efficient it'll be. Wayne's suggestion to run a wire around the top of the walls of a room will do much better for just that reason and be a whole lot cheaper. Of course, using any antenna indoors subjects the RF to losses in the walls, wiring, etc. of the building. AA5TB has a nice on-line article about his work with small transmitting loops and a whole bunch of links to web sites of other Hams who are working with them. It's at: http://www.aa5tb.com/loop.html No one is going to rewrite Maxwell's equations any time soon, but these guys are all doing what they can to squeeze the most out of what they've got to work with. Some of their work is very interesting. But, like almost all Amateur antenna work, results are based on on-air checks are less than meangful when you consider that a couple of watts of radiated RF can, under the right conditions, be copied around the world. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Does anyone know how directional these small loops are? I believe they're
bi-directional, but I wonder how deep the side nulls are. I wonder how well one would work as a receive-only antenna for nulling QRM or QRN coming from a particular direction? Thanks & 73, Jeff WB5GWB _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: MFJ-1782 Loop Antenna as a Receiving Antenna?
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Jeff WB5GWB wrote:
> Does anyone know how directional these small loops are? I believe they're > bi-directional, but I wonder how deep the side nulls are. I wonder how > well > one would work as a receive-only antenna for nulling QRM or QRN coming > from > a particular direction? ------------------------------------------------------------ Jeff, The only one that I have seen close up had very deep and sharp nulls off the sides, how far down I don't know, but yes bi-directional. The owner was using it on 40m and the loop was outside. 73, Geoff GM4ESD _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Fred (FL)
I've used 6' diameter, single-turn-of-hardline loops on 80
and 160 for many years ... with simple transistor amps built into the termination boxes ... and fed via (cheap) CATV type RG-59 over hundreds of feet. Two have been powered 24/7 for over 20 years (!). Yes, if built carefully they have VERY deep and narrow, but equal nulls off the sides ... or put another way, along a line through the loop. I found there's little (no) need to rotate them UNLESS you want to use the null to attenuate the signal from a nearby station ... as in a contest situation. A word of caution ... if building for transmitting, the currents in the loop ... and the tuning capacitor ... will be extreme. There will be heating and since the Q is so high this will result in drifting of the resonance point. This is the main headache for transmitting loop builders. I had the use of AEA's very first production-line loop many years. It worked very well. 73! Ken Kopp - K0PP [hidden email] or [hidden email] _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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