Thought you might like this helpful fix for your HT to increase its performance.
This simple addition of a counterpoise can be used on many of the older HTs or newer ones as long as there are metal screws connecting to the ground side of the antenna.

I did some studying on how to get an old Radio shack HT model HTX-420 to TX and RX better.  I added a counterpoise for the HT antenna and now I can at least get into and talk on the local repeater from my home.  Before the addition of the counterpoise, to the HT, I could key the repeater but no audio.  I did some research and decided to try the counterpoise.  A counterpoise is a conductor used as a substitute for ground in an antenna system.

This is a very simple fix to help the HT to TX and RX better.  You need a small connector (one with the hole in it) and about 19" of small wire (wire from an old discarded wall charger works great or use most any wire you have laying around). See typical connectors here. Strip a small amount from the end of the wire, and insert into the connector...crimping the connector to the wire gives a good electrical connection.

Remove the antenna.  Next take a multi-meter and with one probe on the ground of the antenna and check for a screw in the chassis that has continuity with the antenna ground.  Connect the wire to this screw.  Make sure to test continuity after securing the wire/connector with the screw.

 
Photo above shows counterpoise wire connected to a screw on the back of the HT


Checking continuity between screw and ground side of antenna

That's all there is to it. 73, K5LUO