HELP!!!

Tune the radio with a SWR meter...
Trying to transmit with that problem you are having WILL BURN OUT THE RADIO if it has not been damaged already!! The fact you can transmit when you touch is, but not when you don't, it a sign that some wiring is wrong..the fact you have it mounted to a PLASTIC mirror means it is likely that the grounding is bad...or the grounding strap is being seen as part od the antennae...throwing off the SWR.

 

also need different coax for dual antennas

lotsa info here........http://www.firestik.com/Tech_Docs.htm

RG-58 type: This type of coax is used for single antenna installations and for jumper wires that go between the radio and a test meter (SWR meter). The RF resistance of this type of coax is 50-ohms. Within this group you will find coax labeled with RG-58 or RG-58/U. These cables have a solid center conductor. The second type is RG-58A/U and they have a center conductor made up of many thin wire strands (normally about 17) that are twisted together to form the center conductor. The common outer diameter for this type of cable is about 0.20".
RG-8X: This type of coax is also used for single antenna installations or jumpers between pieces of equipment. Sometimes it is refered to as "Mini-8. Like the RG-58 type coax, RG-8X also provides 50-ohms of resistance. In short, this cable could be called hi-performance 50-ohm cable. It always has a stranded center conductor and a high shielding percentage. It will also handle higher power (wattage) and has a higher propagation velocity. For the general user, it is more than what is required. However, if you are using amplifiers or just like to get the absolute most from your set-up, it will deliver. The outer diameter of RG-8X is typically about 0.24".
Several times a year we get tech calls from installers who place dual antennas on their vehicle and run RG-58 or RG-8X from each antenna to a T-connector at the back of their radio only to find that the system "doesn't get out". You should not use 50 ohm coax on a ground plane dependent dual antenna installation ... it MUST be 72 ohm RG-59 type coax. These flawed installs can be misleading because SWR tests can show exceptionally low SWR, making the installer think that all is well. However, the impedence of the antenna system does not match the requirements of the radio and therefore, the output power of the radio is greatly reduced. In several tests, we found that a 4 watt radio would only generate 1.75 watts of output power which is the equivalent of having an SWR reading that exceeds 6.0:1.
RG-59 type: This type of coax is used for dual antenna installations only. The RF resistance of this type of coax is 72-ohms. Within this group you will find coax labeled with RG-59 or RG-59/U. These cables have a solid center conductor. The second type is RG-59A/U and they have a center conductor made up of many thin wire strands (normally about 19) that are twisted together to form the center conductor. The common outer diameter for this type of cable is about 0.22".

 

If you are using regular stranded wire for your ground that may be part of the problem as well. The rf will sometimes see that as an extion of the antenna and thats not good. You should always use braided ground straps for grounding.

 

I strongly suggest that you carefully read the topic "How to deal with high SWR in newer trucks" thread in this forum. Pay particular attention to the link to the Wilson antenna link.

While not your main problem, any excess of that 18 feet of coax should NOT be coiled up. Rather it should be bundled in the form of a figure eight that is approximately 12 inches in length.

Using an external SWR meter, a reading of 3.0 or higher (excessive SWR)means that you have a connection problem. Continued use of the radio with an excessive SWR reading will damage the radio.