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6

In tuning a trap there are two concerns which are somewhat contradictory: You want the trap to have a high impedance on the target band. You want losses to be low. The objective of a trap is to reduce the currents on the inactive portion of the antenna to a negligible amount. This doesn't require an impedance that's as high as possible: it requires only an ...


4

While your specific implementation will include numerous variables which are difficult to account for, I ran a NEC-2 model to illustrate the direction of a solution: Vertical element: 8.5-m tall 2-in diameter conductor, elevated 0.1-m above ground Radials: 8 x #14 wires, elevated 0.1-m above ground, that are $\frac{\lambda}{4}$-wave on 40m (10.5-m) Trap: ...


4

I am very pleased that my traps have started working properly! The problem was solved by mica capacitors. It turned out that the ceramic capacitors I used had poor temperature and capacity parameters. Mica capacitors have proven themselves perfectly and the frequency does not shift any more. I made the antenna for the bands that I like best 20/40/80/17 / 30m....


3

What you describe does indeed sound like a thermal issue. If you have some unstable components, even a small change in temperature which is difficult to detect can be sufficient to cause the issues you describe. Are you tuning the trap such that its resonance is in the 20 meter band? This would mean when you transmit on 20 meters, current circulating in the ...


3

I don't know how much of an impact it might make, but you might try moving the trap resonance to be outside the 20m band. Trap losses are highest at the trap's resonant frequency because at this frequency the current circulating between the inductance and capacitance is at a maximum. Thus, ohmic losses within the trap are maximized. At resonance is also ...


2

You can put a one-turn loop on the analyzer and use that to couple into the trap. There will be a dip in SWR where the trap is resonant. Here's a picture from the RigExpert manual: Connect that single-turn loop as if it were an antenna, and do an SWR sweep. The notch is the resonant frequency.


1

My quick opinion is that this looks reasonable. A trapped dipole will likely have a smaller bandwidth than a regular dipole. A short simulation is what is required to be sure. You're getting 5% bandwidth at 40 m (the traps don't load it very much at 40 m) which is normal. And to be generous 1% at 20 m. The traps are working on the high impedance tips of the ...


1

Well, since I resolved mystery, here is short explanation. I built my own dip adapter exactly as explained by Phil - single loop of wire connected to output of MFJ-225. However, putting loop at the side of trap (as presented in RigExpert picture) did not work. Dip measurement is quite insensitive, so I had to make sure loop is set at the center of trap ...


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