I put together a fan dipole the other day, just playing around a bit. I took down a 40m OCF (that was working well) and put up a fan dipole with 40m, 20m, 17m and 12m elements built from surplus 12 awg well wire. What I put up plotted out OK on an SWR scan, but the 15m portion sat a bit higher than desirable (the 15m dip was lowest at 22.080 with an SWR of 1.36). I had posted a copy of the SWR scan on another board & got a comment suggesting I look into adding a dangling wire as a capacitance hat on 40m to improve 15m.
The SWR bandwidth for any practical wire size should be sufficient to cover the 40m phone band, and probably the whole band (depending on ground loss, etc.) I have a 40m dipole for portable use that I have put up in a number of situations without adjusting the length or using a tuner - it uses #22 stranded wire.
I did some searching and reading, then followed through with wire and solder & thought I'd share the results.This is the first hat I tried. Made of 24' of solid 12 awg and per some of my reading, rather than letting it dangle, I shaped it into two lobes. These were soldered to the 40m elements at about 10' from the feed point:Here is a SWR scan showing before (fine line) and after (bold line) the cap hat was put in place:As you can see, the cap hat moved only the 15m dip, over to 21.660 @ 1.23.Wanting to see what would happen, I made another set of hats and attached them at 90 degrees to the first ones:Here is the scan made after the modification:The dip for 15m is now 1.19 at 21.480.
The highest SWR in the 15m phone band is less than 1.45:1.I am pleased with the way this turned out, with the general class 15m phone band under 1.5:1 SWR, & thought I'd share.Nick. Click to expand.Actually, a half-wave dipole resonant at 7.1MHz is 3/2-wave resonant significantly higher in frequency than 21.3 MHzThere's not a simple 3:1 relationship, as is well illustrated by the 'cutting formula' from older editions of the Antenna Book:L(ft) = (N-0.05) x 492 / F(MHz)where N is the number of half-waves.That formula predicts a 7.1MHz half-wave would be 3/2-wave resonant at 22MHz - just as the OP found, and makes the need for the capacitance hats even more acute.Steve G3TXQ. Click to expand.Steve -YES, if you run ENZEC. The 15 meter resonance point will be outside the 15-meter band.HOWEVER, it is a Relationship about ODD Multiples of a Half-Wavelength Dipole (and feedpoint Z)that should be Learned (or Memorized) by new operatorsIn practice, of building these antennas (40-meter, 1/2-wave dipole) since high school (40+ years ago) -the actual resonance point at 15-meters varies considerably based on antenna materials, construction, and height above the ground.The other characteristic of a 3/2-wavelength dipole, that is forgotten, is its different pattern (4-leaf clover, with reduced 1/2-wave lobe). Longer wavelength multiples produce more complex radiation patterns. Yes, there are many variables - height above ground, wire diameter, insulation/no insulation, ground conditions etc; but a key principle is that the shortening due to 'end effect' which leads to the familiar 468/F cutting formula is only present on one half-wave of a 3/2-wave wire; the 'middle' two half waves are very close to the free-space value of 492/F.
Hence the ratio of the resonant frequencies will always be significantly greater that 3:1.It's also worth noting that the feedpoint resistance of a resonant 3/2-wave is typically a lot higher than that of a half-wave. It would be interesting to look at whether the 'capacitance hats' affect that at allSteve G3TXQ. I think this is more feasible with a monopole config, playing with it I got things running very nicely in the sim with a small cap hat 1/3 of the way up a 40m vertical - if I recall i just modeled four 0.5m 1/4' spokes, no ring.
Didn't take much. But no matter what I did with a hatted dipole, 15m just had too high impedance to make me happy.Vertical on 15 definitely has that high lobe, but low angles don't look that bad. Match is good especially if you lengthen a bit and run a series feed cap. Seems like a good 'freebie addon' to a full sized 40m vert to give you backup 15m action.
To anyone looking to acquire commercial radio programming software:Please do not make requests for copies of radio programming software which is sold (or was sold) by the manufacturer for any monetary value. All requests will be deleted and a forum infraction issued. Making a request such as this is attempting to engage in software piracy and this forum cannot be involved or associated with this activity. The same goes for any private transaction via Private Message.
Even if you attempt to engage in this activity in PM's we will still enforce the forum rules. Your PM's are not private and the administration has the right to read them if there's a hint to criminal activity.If you are having trouble legally obtaining software please state so. We do not want any hurt feelings when your vague post is mistaken for a free request. It is YOUR responsibility to properly word your request.To obtain Motorola software see the Sticky in the Motorola forum.The various other vendors often permit their dealers to sell the software online (i.e., Kenwood). Please use Google or some other search engine to find a dealer that sells the software. Typically each series or individual radio requires its own software package.
Often the Kenwood software is less than $100 so don't be a cheapskate; just purchase it.For M/A Com/Harris/GE, etc: there are two software packages that program all current and past radios. One package is for conventional programming and the other for trunked programming. The trunked package is in upwards of $2,500. The conventional package is more reasonable though is still several hundred dollars. The benefit is you do not need multiple versions for each radio (unlike Motorola).This is a large and very visible forum.
We cannot jeopardize the ability to provide the RadioReference services by allowing this activity to occur. Please respect this. Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue.
You just need to do it in the right place. For example:https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html. Anything that will carry the current will work. I wouldn't use 22ga wire to construct a dipole to be fed by a 2 kw transmitter but it should work well for anything up to around 50 watts. Two things to keep in mind are that you need something strong enough to support its own weight without stretching much and smaller wire has a higher resistance.The skin effect becomes important at RF frequencies. The current is concentrated on the surface of the wire at high frequencies which increases the effective resistance of the antenna. Stranded wire has a much higher surface area than the same gauge solid wire.
The more strands in a given size wire, the more surface area. That's why most antenna wire is made up of small size strands.If you are make an antenna for HF frequencies then I wouldn't use anything smaller than number 16 for frequencies over 20 MHz or 14 for under 20 MHz. The minimum size of wire for any dipole antenna is the one that will support it's own weight and a little bit more if it has to support the feed line too. That minimum size isn't just for dipole antennas but for any that have to support their own weight. It's a mechanical thing, not electrical. The 'surface area' thingy is a matter of size in relation to frequency of use.
In the VHF/UHF regions it's certainly possible to use a diameter of conductor that will be beneficial to some extent. At lower than VHF frequencies that size relation to frequency can get very large very quickly. At 10 meters a 3 inch diameter conductor may have some slight benefit.
At 80 meters that 3 inchs will turn into something like three feet in diameter to have any benefit at all. There is no noticeable difference between a 18 gauge and 8 gauge wire at 80 meters. There's a way of figuring it if you want to, it's in the ARRL's HandBook.- 'Doc.