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#1
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John S wrote in :
These are complex applications which someone with a mindset not like yours has produced. There will be a learning curve. The important thing is to not get frustrated and give up. If you need help, ask. Understood. Thanks. bear in mind that my mindset did manage to get to grips with phase modulation synthesis, large scale polyphony and multitimbrality, and accurate similautions of a few musical instruments, and did do alone with nothing but expired patents and service manuals, and a very few other published notes to guide me. I'm not trying to show off, my point is that while I do not give up easily, I AM alone, so my time is divided. ![]() my current break from that I go back to it, I might be listening to radio on an antenna or two while not thinking of the antennas for months. I've always been interested in this though, so I won't let it go. I'll look into NEC because the whole thing about good grounds is a particular fascination now, especially if improvising in limited or very temporary circumstances. |
#2
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On 10/12/2014 11:14 AM, Lostgallifreyan wrote:
John S wrote in : These are complex applications which someone with a mindset not like yours has produced. There will be a learning curve. The important thing is to not get frustrated and give up. If you need help, ask. Understood. Thanks. bear in mind that my mindset did manage to get to grips with phase modulation synthesis, large scale polyphony and multitimbrality, and accurate similautions of a few musical instruments, and did do alone with nothing but expired patents and service manuals, and a very few other published notes to guide me. I'm not trying to show off, my point is that while I do not give up easily, I AM alone, so my time is divided. ![]() my current break from that I go back to it, I might be listening to radio on an antenna or two while not thinking of the antennas for months. I've always been interested in this though, so I won't let it go. I'll look into NEC because the whole thing about good grounds is a particular fascination now, especially if improvising in limited or very temporary circumstances. Excellent! I like to explore and I encourage everyone to do so whether it be with math tools or getting your hands dirty. Keep it up. Cheers. |
#3
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John S wrote in :
Excellent! I like to explore and I encourage everyone to do so whether it be with math tools or getting your hands dirty. Keep it up. Indeed. ![]() waiting for someone to make so I could pay for it. I gave up waiting. ![]() Jeff just posted about the perils of antenna towers and hillsides vs NEC2's flat earth, and many earlier things (liek modellign with Sketchup prior to engineering in metals and plastics, have taught me caution. measure thrice, cut once. THis is how and why I want to use NEC, to save me from falling into expensive and time consuming traps, which I think it will do very well. |
#4
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On 10/12/2014 12:09 PM, Lostgallifreyan wrote:
John S wrote in : Excellent! I like to explore and I encourage everyone to do so whether it be with math tools or getting your hands dirty. Keep it up. Indeed. ![]() waiting for someone to make so I could pay for it. I gave up waiting. ![]() Jeff just posted about the perils of antenna towers and hillsides vs NEC2's flat earth, and many earlier things (liek modellign with Sketchup prior to engineering in metals and plastics, have taught me caution. measure thrice, cut once. THis is how and why I want to use NEC, to save me from falling into expensive and time consuming traps, which I think it will do very well. Jeff seems to be a very experience man with RF. I don't doubt his comments about what is possible with a practical situation. I, however, am playing with some fundamentals (free space, antenna characteristics, etc) so that I understand how to catch up to the gurus here. My toy is the modeling program. I do like to compare theory to practical situations, however. |
#5
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John S wrote in :
Jeff seems to be a very experience man with RF. I don't doubt his comments about what is possible with a practical situation. I, however, am playing with some fundamentals (free space, antenna characteristics, etc) so that I understand how to catch up to the gurus here. My toy is the modeling program. I do like to compare theory to practical situations, however. Yep, while nowt is perfect, there is always worth in something as a guide. I got spoiled by op-amps, it's a different thing imagine stuff with actual transistors. Just one example of how tough it can be without the guides. |
#6
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On Sun, 12 Oct 2014 12:03:43 -0500, John S
wrote: Excellent! I like to explore and I encourage everyone to do so whether it be with math tools or getting your hands dirty. Keep it up. This might be useful: http://www.amanogawa.com Java required. Among the "Linear Antenna" animations is a common dipole model, which shows the effects of different element lengths: http://www.amanogawa.com/archive/DipoleAnt/DipoleAnt-2.html I think (not sure and too lazy to RTFM) that "directivity" means gain linear gain. More NEC modeling tools: http://wb0dgf.com/nec-mininec.htm I'm partial to 4NEC2. http://www.qsl.net/4nec2/ It comes with a huge collection of sample antennas suitable for analysis and plagiarizing. Most of my stuff was done with 4NEC2: http://802.11junk.com/jeffl/antennas/ (Not everything shown is my work). There are plenty of tutorials on the web and videos on YouTube showing how to get started with 4NEC2. https://www.youtube.com/results?search_query=4nec2 There is also a multi-threaded engine for speeding up 4NEC2. Highly recommended: http://users.otenet.gr/~jmsp/ If you are into reverse engineering commercial and ham antennas to see how they work, there are a number of collections online. http://www.hdtvprimer.com/ANTENNAS/comparing.html http://www.hdtvprimer.com/SIMS/ http://www.qsl.net/kp4md/modeling.htm http://www.arrl.org/antenna-modeling-files If you want to go Googling for .NEC files, try something like this: https://www.google.com/#q=filetype:nec+antenna https://www.google.com/#q=filetype:ez+antenna Some of the commercial antennas I've modeled turned out to be not very good such as this 2.4GHz yagi: http://802.11junk.com/jeffl/antennas/mfj1800/ (Hint: It's a 200 ohm feed, not 50 ohms). One important "trick" is to always run an average gain test on your design. This is a sanity check to make sure your model somewhat resembles reality. There are at least two examples of antennas on my web pile that do NOT pass this test and are therefore impressive looking garbage. The results should be 1.0 for most antennas. http://fornectoo.freeforums.org/run-average-gain-test-t355.html http://www.arrl.org/files/file/Antenna%20Modeling%20for%20Beginners%20Supplementa l%20Files/EZNEC%20Modeling%20Tutorial%20by%20W8WWV.pdf Please do NOT get hung up on using just one modeling program. While the others have different interfaces and file formats, they are often better at doing specific things. For example, I use several yagi design programs to generate the dimensions and an NEC2 deck. I then use EZNEC or 4NEC2 to more closely look at the result, and to add support structures, real grounds, tapered elements, etc. While you can buy programs that will do it all, you don't want to know the price. Testing antennas is also somewhat of an art. A pile of test equipment is always nice: http://802.11junk.com/jeffl/pics/home/slides/test-equip-mess.html For the price of an HF radio, you can buy various "antenna analyzers" and "network analyzers[1]" that will do a good job of emptying your bank account. Being cheap, I just use a "return loss bridge", RF sweep generator, and an oscilloscope. The RLB can be easily built. These are nice: http://www.wb.commufa.jp/ja2djh/html/e_rlb.html Mine are ugly so no photos. There's not much to it. Just plan on blowing out a few diodes: http://www.qsl.net/n9zia/wireless/appendixF.html#11 http://www.qsl.net/n9zia/wireless/pics/rtrn_loss_bridge.png What limits an RLB is that it only shows VSWR or return loss. There's no indication if the antenna is capacitive or inductive. That's not a real limitation as your radio could care less if the 50 ohms it sees is resistive, capacitive, inductive, or a combination of these, as long as the conglomeration works out to 50 ohms. The bad news is that the RLB has to be near the antenna feed point in order to get useful results. That usually means climbing the tower. You can try using it at the xmitter end of the feed line, but I don't recommend it. I recommended to one former friend how to install a coax switch at the feed point, with one port going to an RLB. That worked splendidly until just after he applied 500 watts to the antenna, and fried the RLB diode. Make sure the switch has sufficient isolation and that the RLB input is shorted when not in use. The sweep generator is probably the most expensive part of the puzzle. The frequency range you want to cover is always important. The HF range is covered nicely by cheap DDS (direct digital synthesizer) modules found all over eBay. For example: www.ebay.com/sch/i.html?_nkw=dds+module Add a PIC controller and output amplifier, and you have a sweeper. Or, just buy one: http://www.ebay.com/itm/121362216469 One problem with these is that they don't have frequency markers, but that can be added later. For VHF and UHF, commercial equipment is probably best. If you can find cable TV test equipment, it will usually get you to about 400 MHz. That's three HP8620 sweepers in the pile on the left, none of which work perfectly: http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html For the oscilloscope, you'll need something that is DC coupled. That eliminates most PC sound card based software. For running an RLB, a cheap 2.0 MHz DSO (digital storage scope) works just fine. The tiny pocket size scopes found all over eBay will work, but the screens are too small to see any detail. That might work if you can unload screen captures to a computah and/or printer. That leaves the question of why bother modeling when you can just cut-n-try an antenna until it works? If you want to make one of something, cut-n-try is a very good and efficient way of getting one of anything to work. However, if you're planning on making more than one, or publishing your design for others to copy (or steal), then some clues as to the theoretical possibilities of the design are going to be needed. A few years ago, I worked on a UHF antenna that was sufficiently high in gain, and therefore narrow band, that customers had to order it by the frequency of operation. I beat the NEC2 model to death until everything possible was thrown into the model. U-bolts, mounting hardware, pipes, yard arms, screws, nearby power wires, other antennas, vehicles, buildings, etc. It was massive overkill, but very necessary. When field tests were run on the first few installs, the measured radiation patterns and return loss graphs were perfect. You can't do that without a computah model. [1] Incidentally, I've seen this problem a bit too often with MFJ antenna analyzers and some VNA's. http://802.11junk.com/jeffl/MFJ-269-repair/ If you own an MFJ analyzer, I suggest you stock up on matched diodes for the inevitable rebuild. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#7
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Jeff Liebermann wrote in
: This might be useful:... It it. ![]() do have a habit of staying with one program so I'll be careful about that. I'm already aware that NEC2 and NEC4 and MiniNEC all have things they are particularly good at, so I'll not limit my choices the way I usually might. |
#8
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I need to risk asking something that maybe should be obvious to me, just to
be sure I'm not starting on a very wrong assumption.. As I'm likely to only be listening, when I see a Smith chart or other diagram indicating relative signal transmission strength at some distance and direction, does this follow the rule of many 'simple' transducers, in that the same chart exactly models the sensitivity of the same antenna for reception? I'm hoping it does, otherwise life might get complicated. ![]() |
#9
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On Mon, 13 Oct 2014 03:48:29 -0500, Lostgallifreyan
wrote: when I see a Smith chart or other diagram indicating relative signal transmission strength at some distance and direction, A Smith Chart is a transmission line matching tool and has nothing to do with distance, range, direction, and strength of an RF signal. Reading between the lines, you might be referring to an antenna pattern polar graph, which sorta looks like a Smith Chart while one is under the influence of controlled substances. does this follow the rule of many 'simple' transducers, in that the same chart exactly models the sensitivity of the same antenna for reception? Antennas do not have a sensitivity spec. That's in the receiver. All antennas do is direct the RF in some particular direction, sometimes concentrating it, which is called gain. Antennas do not produce, amplify, or "strengthen" RF. The only re-direct it. I think you might need some help in basic RF buzzwords. It's helpful when we're both using the same terms to discuss the same phenomenon. Google finds several RF glossary lists online. Start with "A" and work your way to "Z" trying to absorb and understand as many buzzwords as possible. I do that when I initially approach a new technology and recently had to do it for optical terminology, of which I know little. If successful, we might then be able to decode what you're asking. http://micro.apitech.com/glossary.aspx http://e-meca.com/tech_papers/glossary.php http://www.amphenolconnex.com/support/glossary I'm hoping it does, otherwise life might get complicated. ![]() Hope is a poor substitute for understanding. Hit the books and enlightenment will hopefully follow. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#10
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On 10/13/2014 11:21 AM, Jeff Liebermann wrote:
On Mon, 13 Oct 2014 03:48:29 -0500, Lostgallifreyan wrote: when I see a Smith chart or other diagram indicating relative signal transmission strength at some distance and direction, A Smith Chart is a transmission line matching tool and has nothing to do with distance, range, direction, and strength of an RF signal. Reading between the lines, you might be referring to an antenna pattern polar graph, which sorta looks like a Smith Chart while one is under the influence of controlled substances. does this follow the rule of many 'simple' transducers, in that the same chart exactly models the sensitivity of the same antenna for reception? Antennas do not have a sensitivity spec. That's in the receiver. All antennas do is direct the RF in some particular direction, sometimes concentrating it, which is called gain. Antennas do not produce, amplify, or "strengthen" RF. The only re-direct it. I think you might need some help in basic RF buzzwords. It's helpful when we're both using the same terms to discuss the same phenomenon. Google finds several RF glossary lists online. Start with "A" and work your way to "Z" trying to absorb and understand as many buzzwords as possible. I do that when I initially approach a new technology and recently had to do it for optical terminology, of which I know little. If successful, we might then be able to decode what you're asking. http://micro.apitech.com/glossary.aspx http://e-meca.com/tech_papers/glossary.php http://www.amphenolconnex.com/support/glossary I'm hoping it does, otherwise life might get complicated. ![]() Hope is a poor substitute for understanding. Hit the books and enlightenment will hopefully follow. Jeff, maybe he is kind of asking about reciprocity in his own way? |
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