Re: Magnetic Loops - Stan
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We also have an excellent article on Magnetic Loops on our elecraft Tech
notes page (about half way down the page). http://www.elecraft.com/TechNotes/tech_notes.htm 73, Eric WA6HHQ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by AC7AC
I went to one of those lectures by Prof Mike Underhill (G3L??) in front of his IEE peers who did not receive his wisdom too readily. It seemed like a one-man campaign. In essence he postulated that a mag loop was more like a short folded dipole and he showed why. The usual calculated losses were insufficient to show why loops worked the way they did.
I once made a loop from 12ft x 4ft sheet aluminium with a huge capacitor 4ft x 6inch vanes spot welded to the ends (that was an education in itself). It was incredibly impractical, but I did it anyway. I measured a 46dB front to side attenuation. I scrapped it soon afterward. David G3UNA ---- Ron D'Eau Claire <[hidden email]> wrote: > Clearly there's a lot of interest in small transmitting loop antennas, so > here are some links I've collected over the past several years that are > still good detailing the efforts of several Hams (I checked them to make > sure they still work ;-): > > Harry, SM0VPO, has several interesting designs including one built on a > "packing crate" about which he wrote: > > " I have been placed in a situation where a landlord denied permission to > erect an antenna. Any form of antenna was unreasonable, even a white-painted > broom handle caused interference!! My dartboard frame did not cause any > interference at all..." and so he evolved his novel and stealthy small loop > transmitting antenna. > > He also describes an 80 meter frame antenna. At the site below, click on > "Projects", then "Antennas" and then look at links under Antennas on the > left side of the page for "80 meter frame ant" and "Packing crate ant". > > http://web.telia.com/~u85920178/ > > -------------------------------------------------- > > David, PA3HBB/G0BZF has this nice page detailing his work with loops at: > > http://www.qsl.net/pa3hbb/magloop2.htm > > At the time he wrote the page he traveled a great deal and writes, " In > order to fill my evenings with something other than foreign television (or > drinking in the bar), I prefer to sit in my room and work the DX on the > radio. Though this situation may not be typical of all of radio amateurs, > the need for a small, effective and portable antenna will surely hit home > with a number of them." > > --------------------------- > > As a sign of the interest small transmitting loops generate, one fellow in > Belgium created a very nice page detailing his loops and the work of others > that ended up swamping him with e-mails, so it was relocated under a new > URL: > > http://www.qsl.net/mnqrp/Loop/Mag_Loops.htm > > It details making loops as well as ideas for making your own low-loss > capacitors to tune them with. > > ------------------------------- > > DJ3TZ built a small loop using copper tubing shown here: > > http://www.qsl.net/dj3tz/loop2.html > > It has a nice fairly self-explanatory photo but most of the links on that > page to other pages are now out of date. > > -------------------------------------- > > > 73, > > Ron AC7AC > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by K2QI
> On Tue, Aug 4, 2009 at 6:38 AM, Svend Spanget > <[hidden email]> wrote: > > > I recently discovered the source of a very annoying noise in my K3. > > When unplugging the USB cable from my USB hub the noise in the > > receiver disappears. How do I get rid of this? I am using HRD, so a > > connection to my PC is really needed... > > 73's Svend, OZ7UV One of the most common sources of USB device related noise is a bad/open shield on the USB cable. First thing to try is a different USB cable. Since you have a hub involved, don't forget to check the cable between the computer and the hub as well as the power supply for the hub. Also make sure the computer is properly grounded to the station's common ground point and the shield has a good contact to the motherboard groundplane and the chassis. If the noise is from the RS-232 side of the USB to RS-232 converter, place a jumper across the RF choke in pin 5 of the RS-232 connector (Elecraft RF Immunity Mod - <www.elecraft.com/K3/mods/ELECRAFT_Application_Note_Improving_the_Immunity_of_ the_Rear-Panel_KIO3_RS232_and_Audio_Connectors_to_RF.pdf>. In addition, consider making your own RS-232 cable using K9YC's suggestions (CAT5 cable with pins 2,3,4 & 7 each on a separate "pair" with the other wire of each pair connected to the shell of the connector). The K9YC cable makes the RS-232 signals "balanced" and cancels any radiated noise using the "magic" of twisted pairs. 73, ... Joe, W4TV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Rick Tavan N6XI
Thanks for the replies, all.
I'm using a laptop PC with 3 USB ports. With mouse, keyboard, harddisks and other devices I am using 3 USB hubs.... Plugging the cable from the K3 directly into a USB port on the PC does not remove the noise. The hub doesn't have a PSU, but there are a lot of small switch mode PSU's in the shack of course. The noise is present regardless of HRD is running or not... It is really not good to keep the log on paper. What can I do? \Svend ____________________________________________________________ TDC Bredbånd for 0 kr. - Spar 695 kr. Se http://tdc.dk/freemailtilbud/ Denne mail er sendt via Mail på TDC Online - Læs mere om TDC's mailtjeneste på http://mail.tdconline.dk/ ____________________________________________________________ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by David Cutter
Mike Underhill G3LHZ had some good ideas but his ideas that the
theoretical loop equations were not valid were totally wrong. When I was active on 136kHz some years ago I used a large vertical loop and got reasonable results - in a QTH where I was severely restricted in what I could use on those frequencies. At one time I more or less proved to myself that the loop was performing pretty much how the theory predicted and G3LHZ's suggestions that it should be 100 times better (or whatever) were complete rubbish. You can find more information on the 136kHz pages on my website, with calculations on both the traditional loop equations and G3LHZ's (very old pages, not updated for yonks, but for some reason still seem the most visited pages on the whole site...). 73 Dave G3YMC On 4 Aug 2009 at 21:57, [hidden email] wrote: > I went to one of those lectures by Prof Mike Underhill (G3L??) in front > of his IEE peers who did not receive his wisdom too readily. It seemed > like a one-man campaign. In essence he postulated that a mag loop was > more like a short folded dipole and he showed why. The usual calculated > losses were insufficient to show why loops worked the way they did. > > I once made a loop from 12ft x 4ft sheet aluminium with a huge capacitor > 4ft x 6inch vanes spot welded to the ends (that was an education in > itself). It was incredibly impractical, but I did it anyway. I > measured a 46dB front to side attenuation. I scrapped it soon > afterward. > > David > G3UNA http://www.davesergeant.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Svend Spanget
Hi Svend,
I do not normally use the KUSB but I have just tried a simple experiment. I measured the change in noise in the following conditions: PR6 - ON PRE - OFF AGC - OFF K3 - SSB mode, 2k7 BW ANTENNA terminated with 50 ohm. Nothing connected to KIO3: +0dBV K3 <> RS232 cable <> PC communicating with K3: +1dBV K3 <> KUSB <> PC communicating with K3: +10dBV K3 <> RS232 cable <> KUSB <> PC communicating with K3: +0dBV All readings +/- 0.1 to 0.2dBV My RS232 cable home made to K9YC design using CAT6 UTP cable is approximately 3 metres long. The presence of band noise naturally masks much of the PC noise but the increase in background noise level at this QTH when connecting the KUSB alone is still approximately +3dBV. With band noise I do not detect any increase in noise due to the RS232 cable alone. With the PR6 OFF and the K3 internal pre-amp on, noise from the KUSB is approximately +.3dBV. It seems in my configuration PC noise is least with K3 <> RS232 cable <> KUSB <> PC combination. Interesting. Maybe others would like to try and replicate this, perhaps using better test equipment than that built into the K3. It might be worth testing to see if this reduction in KUSB noise can be achieved with a much shorter RS232 tail to the K9YC design or even an appropriately wired back to back RS232 gender changer. This set me thinking that it might be a good idea to make a short cable for the K2 I/O to enable use of the KUSB or a regular RS232 cable without the danger of damage to the K2 I/O. I have not had much opportunity to play with the PR6 due to lack of 6M activity here at present other than EME. Regards, Mike VP8NO ----- Original Message ----- From: "Svend Spanget" <[hidden email]> To: "Mike Harris" <[hidden email]> Sent: Wednesday, August 05, 2009 5:54 AM Subject: Re: [Elecraft] Noise with KUSB Hi Mike. Thank you for answering! I have the KUSB adapter from Elecraft. Do you suggest that I make a short cable like you did between the K3 and the KUSB? The noise is specially irritating on 6 m. I don't have a preamp yet, but building one is on my to-do list. What is your experience with PR6? After I discovered the source it has become clear to me, that the noise is on all bands more or less.... My old laptop has a serial port, but I went for the USB solution because I plan to buy a new PC, which likely will only have USB ports. It is not grounded though - I will see if there is possibility to ground the PC. Lots of 73's de Svend, OZ7UV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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> K3 <> KUSB <> PC communicating with K3: +10dBV
> K3 <> RS232 cable <> KUSB <> PC communicating with K3: +0dBV I wonder if physical proximity of the USB-serial adapter to the rear of the K3 is the cause of the problem? Maybe a magnetic coupling into the RX?? I'm guessing. 73 Gary ZL2iFB ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Eric Swartz - WA6HHQ
Thank you everyone who contributed to this thread.
I am quite happy that this kluge works as well as it does so never one to leave well enough alone I went back to the plumbing shop and got them to create 2 cooper pipe sections using the eq of 2in diameter tubing, each 12ft in length. Through the language barrier we agreed that they would use their tubing bender to bend each section into a 1/2 circle and swage one end so the two seconds could be overlapped inserting one into the other for several inches. They said I could pick them up tomorrow. I also got 2 90 degree elbows to form the ends of a new set of piston caps. The sections are just small enough to drag up the stairs to my living room and assemble once inside my apartment. The new loop will have that one joint in the main loop that has to be soldered with a torch. When assembled the 2 in diameter tubing will form a loop that is 8 feet tall giving a few feet clearance in the living room if mounted vertically. The resistive losses should be pretty low for this new loop that should cover down to 80m but be optimum for 40m. I'll try to find another Jennings Vac cap when I go back to California Aug 30. But if not the piston caps work fine. Years ago I built a loop that worked well in a large Jennings cap, the most difficult part was the gear reduction mechanics. I read the German language papers concerning magnet loops written in the 40s when they were developed for submarine use so the whole concept of magnetic antenna had intrigued me for years. Figuring out the tuning range is pretty simple using my Motorola service monitor tracking generator and spectrum analyzer. I'll report back when I get it assembled tomorrow night. Stan ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Gary Hinson
G'day,
I have mentioned in the past that I have noticed, fairly frequently, that sometimes when first powering up my K3 the received audio sounds weak. This evening I was listening to a 20M QSO between an LU and an LA, both S9. I had the distinct notion that for the af gain setting the audio was not as loud as I would normally expect. When this happens I usually turn the K3 off wait a second or three and turn it back on. When I did this the audio output (phones) was hugely increased, no measurements unfortunately but at least +6dB. Given that a power cycle sorts out the problem I'm wondering if there isn't some sort of initialisation problem, something like the logic races of old. I'm not using any extreme agc settings, virtually default numbers. The house is quiet, my ears still work, and I usually use phones and seldom have the af gain (LO) more than 10 o'clock. Has anyone else noticed this? Regards, Mike VP8NO ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Logic races aren't of old... They just happen with narrower margins now...
The other day I was looking at the scope and taking some measurements in the hundreds of femtoseconds... Gotta love it! ~Brett -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Mike Harris Sent: Thursday, August 06, 2009 4:33 PM To: Reflector Elecraft Subject: [Elecraft] K3 Audio Level G'day, I have mentioned in the past that I have noticed, fairly frequently, that sometimes when first powering up my K3 the received audio sounds weak. This evening I was listening to a 20M QSO between an LU and an LA, both S9. I had the distinct notion that for the af gain setting the audio was not as loud as I would normally expect. When this happens I usually turn the K3 off wait a second or three and turn it back on. When I did this the audio output (phones) was hugely increased, no measurements unfortunately but at least +6dB. Given that a power cycle sorts out the problem I'm wondering if there isn't some sort of initialisation problem, something like the logic races of old. I'm not using any extreme agc settings, virtually default numbers. The house is quiet, my ears still work, and I usually use phones and seldom have the af gain (LO) more than 10 o'clock. Has anyone else noticed this? Regards, Mike VP8NO ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Mike Harris
> I have mentioned in the past that I have noticed, fairly
> frequently, that sometimes when first powering up my K3 the > received audio sounds weak. This evening I was listening to a 20M > QSO between an LU and an LA, both S9. I had the distinct notion > that for the af gain setting the audio was not as loud as I would > normally expect. Hi Mike. My K3 is left on most of the time so I haven't noticed it at startup ... But I did notice sporadic significant reductions in the audio level on 30m the other evening. At first I thought it was someone tuning-up zero-beat on my frequency and triggering the AGC, but it wasn't that. Next I thought there might be an intermittent antenna connection but the SWR was fine and the coax cables in the shack, at least, are all fine. I've had a similar problem in the past with a sticky antenna change over relay in the amplifier (sometimes on going to receive the RF level is way down because the relay hasn't properly closed - a quick tap on the PTT usually fixes it, temporarily), but on this occastion the S meter level looked normal. So I'm foxed. I haven't noticed it since. If it happens again I'll take more notice of what's happening and might even record it. 73 Gary ZL2iFB PS The end literally dropped off my K3's AF knob yesterday as I touched it - the knob appears to be crumbling like dry fruitcake. It hasn't been knocked or abused, just used normally. Elecraft kindly already sent me a set of replacement knobs due to the outer ring/knobs cracking over month ago so now I really must make time to fit them! ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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