using 102" whip for mobile scanner

[33kracing]

so i recently installed a uniden bcd996xt scanner to compliment my motorola cdm1250... (in my tahoe if i failed to advise) now... i did not feel like installing an antenna on the roof becuz of holes, drilling in roof, water leakage, etc, etc. so i went with the old fashioned dukes of hazzard and put a ball mount spring antenna on the left, rear quarter panel above and left of the gas cap. now my problem is... with the 102" antenna, it works excellent monitoring the p25 nebraska state radio network along with other analog public safety frequencies. the thing is, i cut the antenna down from 102" down to 74" or just over six feet (down from 8.5 ft) now the signals whether analog or p25 cut out while moving. stationary is just fine... 102" great... 74? not so much. any ideas on how to correct or solutions without sporting a 26 foot antenna that practically reaches the moon? that is/was the only mod that i did that caused the change that im aware of. i can tell when the antenna weaves or bends or whatever u call it on the p25, the signal bars can easily go from 5 down to 2-3 bars if im lucky. thanks in advance!!

 

[davenlr]

Your antenna is no where near being resonant for the system you are trying to listen to.

The correct length of the whip (including the spring which is part of the antenna) is 18 inches.
You would be much better off removing the entire spring and whip, and replacing it with a 5/8 wave VHF high band antenna:
Hustler CG-144 Antenna CG144

 

[33kracing]

Your antenna is no where near being resonant for the system you are trying to listen to.

The correct length of the whip (including the spring which is part of the antenna) is 18 inches.
You would be much better off removing the entire spring and whip, and replacing it with a 5/8 wave VHF high band antenna:
Hustler CG-144 Antenna CG144

even anything on the side-mount?

 

[LtDoc]

Aside from that whip not being close to resonance, it's being 'blocked' by part of the vehicle. Positioning should improve particular stations slightly, maybe. What can you do about that side mount? Nothing that's going to be very 'palatable', sorry.
- 'Doc

 

[davenlr]

The way the colinear antenna I linked works, it uses a 1/4 wave at the bottom (mostly blocked by the cab toward the front, then a two foot tall matching coil, and topped with a 5/8 wave whip, which would be above the cab, and does the most receiving anyway, so it should work well with your side mount on that Nebraska system. If you get it, remember the antenna is actually intended for 146 MHz, so you will need to adjust the 5/8 whip down as far as it will go into the coil, and the coil as far onto the 1/4 wave section as possible to get the antenna resonance up closer to your P25 systems frequency, but it should give you some good gain. I used to use one on my car for two meters, and had no problems hearing out 50 miles or more. This antenna also will screw right onto your spring, or mount without spring, so you wont have to adapt your mount.

 

[33kracing]

welp i got stubborn/bored and swapped out the 74 incher for the 102 inch antenna... for the most part for not having a matched antenna... fixed. only ran into one dead spot that was brief at best. sooooo the mind games and head scratching begin...what to do what to do haha. might look into the antenna that you sent to me. thanks!!