Saturday, January 13, 2018

Dual-Band Antenna Install

I've never been one to be reluctant to drill holes in a vehicle. The NMO (New MOtorola) mount for the dual-band (2m and 70cm)  antenna needed a ¾" hole in the center of the roof which is slightly smaller than the inside threaded piece seen in the picture. The outside thread has a rubber "O" ring to seal against the roof. The inside has “teeth” which dig into the painted surface on the other side of the roof to establish a good ground plane for the 5/8 wave antenna. Silicone grease is used on the “O” ring to ensure a watertight seal.

To protect the contacts and the threads when an antenna is not installed, a cap is screwed onto the mount. To do the install, I needed to mostly remove the headliner. Not only to route the cable but to locate the roof supports. I didn’t want to drill into them but wanted to be right next to one. Fortunately, the headliner in the truck can be lowered easily and the antenna cable is routed down the driver's side “B” pillar. 

For now, I’m just planning to use the antenna with the 8 watt Baofeng HT using an SMA to SO-239 adapter. I'd like to eventually pick up a mobile HF radio that also includes UHF and VHF. In this case, the main chassis will probably be mounted under the driver's seat. Before buttoning up the headliner, I used an ohmmeter to see if the "teeth" on the mount dug into the paint. The ohmmeter claimed 0.8 ohms so all is good at least as far as the antenna is concerned.

When testing the setup, I could clearly receive the call sign from the repeater but what is uncertain is whether my signal is reaching it. The pin on the SMA adaptor didn't look like it would actually reach the antenna contact. When I tried asking for a test, there was no response. I also don't have an SWR (Standing Wave Ratio) meter so I can't really test things. Actually, I do have one that I purchased 40+ years ago but I haven't seen it for over 20 years. Who knows what box it's in. So more research is needed...

5 comments:

redlegsrides said...

Man you're really getting into this ham radio thing....now if only one could get internet access via ham radio...

RichardM said...

Actually, I’m still exploring it. There is always the emergency communications aspect and being in AK, the very low power and/or low bandwidth communication methods are interesting. BTW, there are those setting up mesh networks using amateur bands and Winlink is for email over radio. Again, very low bandwidth so no web surfing with any of these technologies. But still interesting to explore.

Artie & Leinen's Grand Adventure said...

No drilling holes in the Prius unless it is to install a sun roof.

RichardM said...

How for a cup holder. I hear that Prius' only have about 9.

david R said...

SWR meter, might have one and I know where it is, assuming its a SWR... how about a kilowatt hf amp?