Batboard

Hello all. Just looking for some thoughts on what you feel the best VHF mobile antenna is that won't exactly break the bank. This will be for my personal vehicle. Currently, we operate on 151.430/155.895 wide band but will very soon be switching to 151.0625/159.3825 narrow. The radio I use is a CDM1250. I currently have a comtelco base load whip antenna, but as of late, it doesn't seem to be picking up or transmitting as well as it used to. Any thoughts are greatly appreciated.

How are you going to mount the antenna? Are you thinking of drilling a hole in the roof or do you want something that doesn't require a hole in the vehicle? Is this a car, van, SUV, or something else. Will these vehicle go into garages with low clearance often?

What style 1/4 wave or 5/8 gain? Before you spend money to change an antenna. Check the mount. Corrosion of the center pin can cause issues. How is the antenna mounted now. Drilled in NMO, Trunk lip magnet? There may be underlying issues causing the loss of performance. Also take a continuity tester to the cable as it may be shorted.

It is a 5/8 gain. Currently mounted on an L bracket on the rear fender. It used to work pretty well, but now it seems that my portable would pick up better in some cases.

FireCpt809 wrote:What style 1/4 wave or 5/8 gain? Before you spend money to change an antenna. Check the mount. Corrosion of the center pin can cause issues. How is the antenna mounted now. Drilled in NMO, Trunk lip magnet? There may be underlying issues causing the loss of performance. Also take a continuity tester to the cable as it may be shorted.

I have to agree and now that you said its on a l bracket I would check the cable and mount. I have seen the cable rot/corrode off the center pin or break off. a quick continuity check should find the issue quickly

Thank you for the help. I switched the antenna with another one I found laying around and it seems to have improved a good bit. I will also check the cable for good measure.

If the NMO mount is the type where the center conductor and cable braid are exposed where it attaches to the mount, moisture/water/liquid road grime and carwash soap gets into center conductor and the braid and creates impedance changes and corrosion, especially when the exposure includes forced spraying such as in car washing. Even though the metal of the center conductor and braid doesn't absorb water, the fact that it is tightly confined by the insulation creates the ideal environment for the natural capillary action of water. Because the outer conductor is braided, that makes it act as a wick to liquids, and the soap enhances the capillary action by reducing the surface tension of water, and worse, introduces corrosion inducing alkalies to the mix. The moisture holding action of tightly confined twisted wire and outer conductor braid combined with a lack of air circulation in the spaces they occupy inside the jacket gives the process a long and gradual degradation instead of a rapid effect.

Cable contamination isn't usually a problem for hole mounted installations because the cable isn't usually exposed to weather and car washing at the mount, but the reality is that bracket mounts need the mount end of the cable sealed where the braid and center conductor are exposed on the underside. If you can seal the cable during the initial installation where the conductors are exposed or use the factory crimped non-exposed type of mount such as a Radiall Larsen NMOKHUD mount and cable, that should help prevent the degradation process. Even the crimped non-exposed type needs to be sealed at the crimp to keep the soap from eventually allowing water in if mounted out in the elements.

If there's nothing obvious upon visual inspection and a continuity check doesn't reveal anything, an SWR meter, or much better yet, an antenna analyzer, will tell the truth about the feedline and the connection properties.