2M / 70cm upgraded trunk mount/antenna gets horrible results

[MarkAugie]

I’m new to Ham Radio and using mobile rigs. So this question is probably generic to any vehicle, but I thought I would ask here, since it is a Leaf.
I was using a mag mount antenna with my Kenwood TM-D710A radio. It worked OK, but thought I would get better reception and transmission with a trunk mount antenna.
What I got as an upgrade::
K412SNMO Trunk mount
NR-73BNMO antenna.

Wow, the reception is horrible, and my transmissions are so bad, ARPS will not even get a beacon shot through to the repeater.. I am wondering if i need to scratch off some paint for a better ground? Bad location selected? Attached is a photo of my mount/antenna.

I have no idea why my cheap mag mount would have such better results.

I am interested in what others have done regarding antennas and how happy they are with the results and any ideas what I am doing wrong.

For me, my transceiver, battery and head unit are setup for a ‘go box’ The only permanent thing i keep on the car is the antenna.
73

https://docs.google.com/file/d/0B0CI3OO--1ypQlVkb0sxLTV6VG8" onclick="window.open(this.href);return false;

 

[TomT]

Assuming that both antennas are resonant (a swr meter or the like will tell you), it may be antenna placement...

Perhaps the mag mount was nearer the middle of the roof and the trunk mount near the edge... This can produce a very non-symmetrical pattern and might be part of the problem.

Another consideration is the length of the antenna... Perhaps the mag mount was 1/2 or 5/8 wavelength and the trunk 1/4, which would give the mag mount more gain...

Lastly, it might be coax quality and/or length...

Just some thoughts...

Tom K6TGT

I have no idea why my cheap mag mount would have such better results.

 

[gbarry42]

I would expect the mag mount to work better if it was indeed on top of the car (center of the roof, even). The trunk mount puts the antenna near the body which can block the signal and throw the antenna tuning off. By the way, at 70 cm and beyond, the quality (and length, and number of adapters) of the feedline starts to matter.

Finally, if the difference is like 10dB or more...well, the antenna could just be defective.

 

[MarkAugie]

Thanks for the help. Wow, that was quick.
I did discover the problem, and I feel stupid. The antenna was not screwed all the way into the mount.

After getting home from work, i took a closer look. Once screwed in all the way, it works much better.

Thanks again.
73

 

[GlennD]

One problem with the edge lip mounts is that they come with 18 ft of teflon rg174 'low loss'. Teflon does not make it low loss at UHF. When I used one on my Accord I transitioned to RG142 after the cable made it to the underside of the trunk.

On my Leaf I use a NMO mount on the roof for very good ground plane performance.