What's inside MPAS Chameleon Hybrid Base Mini

[Sergei_UB4LDT]

The contents of the base of the MPAS Chameleon Hybrid antenna cannot be found in any way.
Judging by the brief description and my guesses, there is some matching device there that coordinates the resistance of the vertical and radial conductors into a resistance close to 50 ohms, the output resistance of a shortwave transceiver.

I would like to repeat this ingenious design on my own.
What I would like to ask from forum participants who have a similar antenna.
To measure all possible combinations using the simplest amateur radio devices, a multimeter in the ohmmeter mode, this is direct current measurements, and alternating current measurements, using an LC tester, or a multimeter, if it has similar functionality.

 

[K6GBW]

Chameleon frequently uses a 5:1 unun for their antennas. I'm betting that's what it is.

 

[Sergei_UB4LDT]

Chameleon frequently uses a 5:1 unun for their antennas. I'm betting that's what it is.

it turns out that the transmitter operates on a 250 ohm resistor via un-un 5:1 ?

 

[prcguy]

it turns out that the transmitter operates on a 250 ohm resistor via un-un 5:1 ?

No, the Chameleon, some Alpla Antennas and the Comet CHA250B use a broad band 5:1 transformer to change the impedance from 50 ohms to about 250 ohms to better match up with the varying feedpoint impedance over a wide frequency range. There is no 250 ohm resistor in these antennas and the transformer directly feeds the whip or wire.

I have a Chameleon MPAS and an extra 500w rated 5:1 transformer. I got them more for testing but don't really use them. There are lots of diagrams and build it plans for this type of transformer and you can even buy a kit on eBay. One of the better ways to test a transformer like this is with an antenna analyzer or vector/scalar network analyzer and a 250 ohm resistor across the output leg of the transformer. You can test insertion loss buy testing two transformers in series then dividing whatever loss you have by two.

 

[Sergei_UB4LDT]

Thus, the MPAS Chameleon Hybrid Base Mini has a similar structure as the base of the Comet CHA 250 antenna, do I understand correctly? That is, it is un-un with losses, which is ultimately expressed in the ability of the antenna beam to work at any frequency, regardless of the size of the beam and frequency.

 

[prcguy]

Thus, the MPAS Chameleon Hybrid Base Mini has a similar structure as the base of the Comet CHA 250 antenna, do I understand correctly? That is, it is un-un with losses, which is ultimately expressed in the ability of the antenna beam to work at any frequency, regardless of the size of the beam and frequency.

Sort of, its a broad band impedance matching transformer. It has loss but not that much when operated within certain limits. Its use in the antennas listed is to take a potential extreme impedance fluctuation of below 50 ohms to maybe 2500 ohms and reduce that to something more manageable for an antenna tuner. The stated useful range of these is roughly 1.8 to 60MHz.

 

[Sergei_UB4LDT]

Thanks for the information. There is enough information about the independent manufacture of an analog of the Comet Cha 250 antenna on the Internet. I will consider whether to spend time and materials on the manufacture of a matching transformer.