MFJ - 1750 Antenna

[mrslacker102]

Does anyone know if this antenna can be trimmed for different frequency range like 150-155 mhz?

 

[ka3jjz]

It appears that there is a matching network near the base of the antenna. You would have to retune or adjust it to get the antenna to optimally work on the 150 Mhz area, but it could be done. Probably more work than its worth, frankly

Why not build something? Even the off center fed dipole we have in our wiki would likely do a better job.

Mike

 

[jwt873]

It is probably tuneable through cutting.. The Larsen NMO150 5/8 antenna has a loading coil a the base and it covers from 144 to 174 Mhz. Larsen supplies a chart to show how much to trim for the desired frequency.

If you have a VHF SWR meter, you could nibble bits off the end until the SWR gets down to where you want it. To be certain, best bet would be to get in touch with MFJ. MFJ Enterprises Inc.

 

[ka3jjz]

The elements could be cut, but according to the ad, there's a shunt fed matching network at the base (take a closer look at the pic). It would need to be retuned for optimum reception. Again, it's possible, but since there are so many better options out there, I kinda doubt that it's worth the effort

Mike

 

[dave524]

For receive I would leave it as is, don't think you would gain much signal even it you did tune it. If you want to transmit that is a different kettle of fish. If it doesn't work out for you resale would be better if unmodified.

 

[Ubbe]

Does anyone know if this antenna can be trimmed for different frequency range like 150-155 mhz?

Sure. The coil at the bottom are an impedance match and to get DC ground to avoid static buildup. It has nothing to do with the lenght of the element, its no loading coil.

It is now tuned to 146MHz and if you want it tuned to 153MHz you make it 146/153=95% of its original lenght.
It's no more complicated than that. If you would like it to be an airband antenna tuned to 125MHz you buy a new element or lenghten the one you have to make it 146MHz/125MHz=117% of its original lenght.

The lenght of the element for a 5/8 wave antenna are 300 divide by MHz multiply with 5 and divide by 8 to get the answer in metric meters for a 5/8 antenna and then make it 5% shorter to compensate for the surface delay (velocity factor) of the material of the element. One meter is 3 feet.

/Ubbe

 

[bb911]

For receive I would leave it as is, don't think you would gain much signal even it you did tune it. If you want to transmit that is a different kettle of fish. If it doesn't work out for you resale would be better if unmodified.

I agree. Over the years I've used many different scanner antennas. My best widebands were 2m ham j antennas -- 39 to 900Mhz.