Ive never understand why Radio Manufacteurs makers dumped the 25.000-88.000 mhz commercial vhf lowband fm so quickly , it has fantastic properties over VHF Hi-Band out in the open or hilly terrain. Think Moto USA used to make them. As for the antenna changing, you have to bear in mind most helicals are typically -6dB loss (roughly) So that 1Watt input,only going to radiate around 0.25W ERP! at 5w input,around 1.25W ERP In real terms thats about 1 S-Point. Ive been doing tests with Tactical tape antennas they do work well with a gooseneck extender,those maybe another option. "Height is Might"-with VHF HI/UHF on fringes area. Great vidio,imformitive! 👍Rob.P
My guess is that your telescopic antenna is a 5/8 wave antenna when extended. When collapsed it is non resonant and you have a very high SWR and the radio rolls back the power to protect the finals.
Its worth a try but in our experiments it doesn't work as well as you might think, so we did not include it in this lesson. Dr Durkin calls this technique the Lloyd Dobler maneuver. If you do or dont get the reference: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-S5Y8tFQ01OY.html