+++++++++++++++++++++ Date: Mon, 25 Mar 2002 21:30:00 -0500 From: "Dave" To: "Low Power Amateur Radio Discussion" , brownh at hartford-hwp.com Subject: [123210] Re: The snake antenna The Snake antenna is used usually as a receiving ant. for the lower frequency hf bands like 80 meters or 160 meters The received signal is a much much lower level than an elavated antenna but most "noise" is absent. The signal is sometimes then amplified by the use of a simple external preamp. It is not a suitable transmitting antenna. you can read more on this in W1FB's antenna note book and ON4UN's low band dx hand book Hope this of a little help Dave W1QB ++++++++++++++++++++++++ Date: Mon, 25 Mar 2002 21:16:47 -0600 From: "Gordon Couger" To: , "Low Power Amateur Radio Discussion" Subject: [123215] Re: The snake antenna It's a very poor transmitting antenna but not unusable. Experiments with underground transmitting antennas on 80 meters worked with a very great deal of loss. Some cavers use 80 meters for underground communication. If you can find anything better use it but if that is all you have give it a try. Dropped down the face of a building is another thing all togeater. If you can get it away from metal columns or reinforcing steel you may do pretty well. most building materials have a dialectic constant of 3 to 5 and reasonably transparent to HF. On 40 & 80 meters you will not be able to get far enough away from the supports that they don't have a considerable effect on you signal but on 20 meters and up you may be surprised. Drop it out the center of the window if you don't have a way to detect the support beams in the wall. From: "Haines Brown" : Someone the other day spoke of a "snake" antenna that consisted of a : simple coax laid out on the ground with the far end shorted. : : I'd like to find a discussion of such a beast. Can anyone direct me? : : Would it world dropped vertically to lay alongside a steel building : rather than horizontally along earth? : : Haines kb1grm +++++++++++++++++++++ Date: Mon, 25 Mar 2002 19:25:06 -0800 From: "Trevor Jacobs" To: , "Low Power Amateur Radio Discussion" Subject: [123216] Re: The snake antenna Lowfer (1750 Meter Band) is much better for caving. I'd imagine that 80 meters isn't too effective underground. 72/73's Trev KG6CYN ++++++++++++++++++++ Date: Mon, 25 Mar 2002 22:12:25 -0600 From: "Gordon Couger" To: "Trevor Jacobs" , "Low Power Amateur Radio Discussion" Subject: [123220] Re: The snake antenna Of course the lowfer band works better but 80m and 160m will work at reduced depths. Even 27 MHz CB handy talkies have been use to map lava tubes. The availability of equipment often makes compromise necessary. Magnetic antennas work by far the best for underground radio. See http://www.caves.org/section/commelect/mm/mm05.html showing that 1.8MHz as a predicted upper limit was pessimistic. No one would design an underground radio above using a frequency 100 KHz. But in an emergency one might have to make do with what they had. 72 Gordon W5RED ++++++++++++++++++++ Date: Wed, 27 Mar 2002 00:13:16 +0000 (GMT) From: J.Bennett at lboro.ac.uk To: qrp-l at lehigh.edu Subject: [123286] Re The Snake Antenna Hi Haines et al, The snake antenna is indeed a length of coax with the far end shorted, but the braid is open at the feed point also.At this point a high voltage is generated, so it is best to insulate the coax at this point, and at the shorted end to stop ingess of moisture. I have tried various lengths on different freqencies, and I can vouch that the antenna does work either in an horizontal plane or in the vertical plane, or indeed at any angle in between. I have to say though, the performance of this antenna cannot be described as startling, and may even be described as mediocre! One thing is for sure, it raises a few eyebrows! Good Luck with your experiments. Jack G3PVG ++++++++++++++++++ Date: Tue, 26 Mar 2002 18:22:38 -0600 From: "Stuart Rohre" To: Cc: Subject: [123288] Snake antenna The Snake, a coax sometimes with a 0.01 disk cap at end and about a quarter wave, is used as a receiving antenna for lower noise on 80M and 160M. It would work best NOT near other conductors like a steel building. The idea is although on the ground and thus picking up less signal, it will also pick up less electric field noise from noisy overhead power lines. This is a NVIS antenna from all reports of some who used it and did a program for one of our local clubs. 73, Stuart K5KVH ++++++++++++++++++ Date: Wed, 27 Mar 2002 14:38:05 +0000 From: "Leon Heller" To: rohre at arlut.utexas.edu, qrp-l at Lehigh.EDU Subject: [123317] Re: Snake antenna > >The Snake, a coax sometimes with a 0.01 disk cap at end and about a quarter >wave, Co-ax terminated in the line's characteristic impedance is often used as a 'leaky feeder' antenna for RF comms in railway tunnels. 73, Leon -- Leon Heller, G1HSM Tel: +44 1327 359058 Email:leon_heller at hotmail.com My web page: http://www.geocities.com/leon_heller My low-cost Altera Flex design kit: http://www.leonheller.com ++++++++++++++++++ Date: Wed, 27 Mar 2002 09:36:02 US/Central From: delphinus at brightok.net To: qrp-l at Lehigh.EDU Cc: brownh at hartford-hwp.com Subject: [123324] Re: Snake Antenna A good description of the receiving uses of the snake antenna can be found in April 1988 QST. The article is entitled, "On-Ground Low-Noise Receiving Antennas" and is by Doug DeMaw, W1FB. You ought to read the article yourself, but the highlights that stuck in my mind were: * Its used for receiving. * It can have low noise characteristics. * Use a pre-amp with it. * It must NOT be an integral number of 1/2 wavelengths long on the frequency of interest. Let us know if you find a way to use it. 73, Matthew AD5AP +++++++++++++++ Date: Thu, 28 Mar 2002 06:43:50 -0700 From: "Conant, Paul" To: "'qrp-l at Lehigh.edu'" Subject: [123378] Snake v. Grasswire I did not see any mention of the grasswire antenna in the thread on snake antennas. While snake antennas are noted primarily as low noise receiving antennas, the grasswire antenna is used for transmitting, although it is definitely a compromise antenna. K3MT describes his grasswire antenna as "an end-fed, longwire antenna that is laid right on the grass." His website at http://users.erols.com/k3mt/grasswire/grasswire.htm gives a brief description of this antenna accompanied with a discussion of reflection and the Brewster angle, an extract from his logbook when using the "grasswire", and details for constructing the balun used to feed it. He also describes how to deploy a "Windom in the Grass". I have not tried these out, but suggest the above URL for another slant on on-the-ground antennas. K3MT notes that "...contacts were made on 80, 40, 20, 15 and 10 meters. The signal reports are not fantastic. But contacts were made, and ham radio was enjoyed! Five countries were worked in 3 days..." Take a look, try it out, and let us know what you think. 72, Paul, WQ5X Here's the correct URL for K3MT's grasswire antenna-- http://users.erols.com/k3mt/graswire/graswire.htm From: George Reeves +++++++++++++++++++ Date: Thu, 28 Mar 2002 08:59:43 -0500 From: Tom Feeny To: *QRP-L Subject: [123379] Re: Snake v. Grasswire Some years ago there was discussion of what was called a "slot antenna" or a "trough antenna" (I think ). It was a wire suspended over a small trench dug into the dirt. After a while I didn't hear anything more about it. I think DeMaw wrote something about it although I don't have a url to it. regards, Tom, W8KOX > K3MT describes his grasswire antenna as "an end-fed, longwire antenna that > is laid right on the grass." ++++++++++++++++++++