Date: Thursday, 24 May 1990 15:34-MDT From: rti!dg-rtp!rtpsql0.rtp.dg.com!harrism at mcnc.org To: INFO-HAMS@WSMR-SIMTEL20.ARMY.MIL Re: MININEC3 Primer (LONG) Here is some help for new mininec3 users who don't have the manual... Segments - you need to tell it, for each wire, how many pieces to break it up into for the computations. In general, the more segments, the better the accuracy, the slower the computations. You should typically use an even number of segments. Pulses - pulses are assigned to portions of the wire based upon the number of segments. Chose the pulse (for source or load) based upon the endpoint coordinates for each pulse. (Look at the geometry output). The pulse will be applied to the middle. Source pulses are how you feed your antenna. the assigned pulse number located where you want to feed it is the source pulse number. Normally chose a voltage of 1 volt and a phase of zero degrees Load pulses - these would correspond to loads such as traps, resistors (as in a rhombic), etc. You normally don't have theses. As an example, take the following wire: (remember - dimensions are in meters....) 0 -5.277 10 5.277 0 10 This would be (roughly) a 20 meter dipole at 10 meters high. The program will compute the connections based upon the coordinates. chose the frequency (say 14.2 Mhz). enter the wire and specify 10 segments use a diameter of, say, .002 meters Note that pulse number 5 cooresponds to the middle of the antenna. (obained from the mininec3 geometry report) specify pulse 5, 1 volt, 0 degrees for the source specify zero load pulses Tell it to compute currents. I got an impedence of (77+J40) for this run. Tell it to compute far field patterns,..... The key is to run it once, with output to disk or printer to get the antenna geometry and pulses, and then to run it again once you know this info (scrolls by much too quickly)... A handy aid it to use mnpre to pre format input for mininec3 based upon file input. Remember that mnpre takes a xxx.NEC file and generates a mininec.INP file (you lose the xxx part ), and mininec3 will *not* ask you for geometry input if it finds the MININEC.INP file laying around. The format of the mnpre file is: GW,,pulses,x1,y1,z1,z2,y2,z2,diameter with a line for each wire. thus, the TEST.NEC input file for our sample run would contain the following line: GW,,10,0,-5.277,10,5.277,0,10,.002 Now, part two of the series answers some common questions and hopefully fills in all the gaps. ------Real questions and answers follow------------------------------------- > Fantastic, all is approaching elightenment. I always get worried when that happens..... > > Only minor problem is that if I have a "bent" wire, such as an > inverted-Vee, do I put that in as TWO wires which have a common end - does yes. Anything that isn't straight has to be broken into discreet straight wires. > MININEC assume wires with coincident (X,Y,Z) are in fact connected? > And if they are in fact insulated, do I just specify slightly different > (X,Y,Z)s ?? yes, and yes. > Doesn't feel right cos it seems too easy! Will try it in a second! ... > I think I am getting my orientation in free space confused ... which only > matters when there is ground --- and when I visualise > ZENITH AZIMUTH VERTICAL HORIZONTAL For the coordinate system, imagine you were looking at the antenna. X would be a distance along the ground pointing at you; Y would be a distance along the ground pointing 90 degrees from X, and to your right; Z is the altitude above ground. For Zenith, imagine your hand pointing straight up at the sky. Then rotate your hand towards the horizon, say 10 degrees. This is a zenith angle of 10 degrees. Thus, the horizon is at 90 degrees. (I looked at alot of strange pattern plots until I figured this out). For Azimuth, the angle is the angle between the X axis and a ray rotating towards the Y axis (looking down from the (0,0,Z) axis, it rotate counter clockwise). Z | | / Q | /| | / | | / | | / | | / | |/ | .______|__________________ Y / \ | / \ | / \ | / \ | / \ | / \| /_____________\ X where theta is the azimuth angle ane phi is the zenith angle. Rotating away from Z towards the point Q is positive zenith angle. Rotating away from X counter clockwise is a positive azimuth angle. -------------------------------------------------------------------------- Part three concerns connections. While mininec3 will automatically compute connections for you, you should check it's geometry output to ensure that YOU didn't make any mistakes. You can do this by checking the connection data of the geometry output. A connection value of zero indicates that the end of the wire isn't connected to anything (*yet*). a negative integer with a magnitude equal to the wire number indicates a connection to ground a negative integer with a magnitude less then the wire number indicates a wire junction. Specifically, it indicates that this end (end1 for example) is connected to the same end (end1 again) of another wire. For mininec3 this number should be the wire number of the previously defined wire that this wire connects to. a positive integer with a magnitude less then the wire number indicates a wire junction. Specifically, it indicates that this end (end1 for example) is connected to the other end (end2 for example) of another wire. For mininec3 this number should be the wire number of the previously defined wire that this wire connects to. I complemented this by writing a script that takes .NEC files and display's them with xgraph. Most errors show up right away! ----------------------------------------------------------------------- The demand for help hasn't been swamping me, so I'd be glad to help people get started (I'm not an expert - I just have the manual!) I've been having luck with X-beams and V beams, but a friend has been having trouble with "parallel" dipoles. Play with it! Hope this gets you started - good luck! Mike Harris - KM4UL harrism@dg-rtp.dg.com Data General Corporation {world}!mcnc!rti!dg-rtp!harrism Research Triangle Park, NC