Questions tagged [trap]

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2 votes
2 answers

Why does my 7 MHz antenna trap have an SWR of 8?

I made a 7 MHz antenna trap. On testing it the cut-off point was 6.687 MHz which is about right but the problem I've got is the SWR was an 8 and wouldn't go down to a resonant SWR. What have I done ...
chris cutting's user avatar
4 votes
2 answers

Building Antenna Trap: Highest impedance/lowest capacitance/greatest # of turns?

I made my first multi band antenna this weekend for 20 and 15 meters for an EFHW wire with a 49:1 unun, to be used with 5 W rig. I used a toroid I had on hand, T80-2. I hang this antenna in my living ...
wbg's user avatar
  • 301
3 votes
2 answers

Antenna traps - problem with frequency change

I built a two-band antenna (20 and 40m) with traps. I made the traps as a parallel LC circuit on the AL7 toroidal core (3 MHz - 40 MHz), I also used a 1KV ceramic capacitor. I've tuned everything up ...
Artur's user avatar
  • 71
3 votes
3 answers

What is an expected SWR plot for a trap dipole?

I've build a trap dipole for 20/40m bands. Traps are made of a coil wound on an insulator of RG213 coax and 3 kV NP0 capacitors. The impedance measured with EU1KY antenna analyzer is following: This ...
Aleksander Alekseev - R2AUK's user avatar
4 votes
1 answer

Using a trap out of its resonance frequency?

I have a vertical antenna, about 7M total length, with a loading coil at 6M height. This is just because aluminium tubing is sold in 6 meter lengths. The loading coil is used to make it resonate at 7....
hjf's user avatar
  • 1,199
1 vote
0 answers

Looking for a formula used by VE6YP trap calculator

I wonder whether the source code of VE6YP (Tony Field) coaxtrap design program (link 1, link 2) was ever published or described. As a Mac user I'm having little difficulties using this software and I ...
Aleksander Alekseev - R2AUK's user avatar
5 votes
1 answer

What frequency to set trap on?

I plan to build trapped multiband dipole so I read lots of documentation I found. There is one thing that confuses me: various authors recommend setting resonant trap frequency differently: some say ...
Pedja YT9TP's user avatar
3 votes
2 answers

Is it possible to measure antenna trap with MFJ225 without help of PC?

I have MFJ225 antenna analyzer. I measure coax trap filters by connecting this analyzer to PC and using IG_miniVNA application. That works fine. But, sometimes I need to make such measurements in ...
Pedja YT9TP's user avatar