Glass-mount antenna on factory-tinted windows?

[Martinjmpr]

Anyone else here running a glass mount antenna? I picked up a Larsen dual-band glass mount for the 2m mobile in my 4runner. Listened to 2m repeaters a bit on the way into work this morning (weather related - we're getting a mild snowstorm today.)

Sound was not that good. I know my signal's getting out because I can hit repeaters but I'm not sure how much of my signal is getting out. I tried a couple of QSOs but got no response.

After I got the antenna I read through the installation instructions and it says not to use it on windows that are tinted or have a metallic film - well, the 3rd gen 4runners have a dark factory tint, don't know if it's metallic or not but it is a dark tint. I have it mounted on the driver's side back window, low on the glass. The antenna is about 19" long with a center coil.

Anyway, I'm just wondering if there's any way to "tune" a glass mount like this. I don't have an SWR meter though I might get one.

BTW, before anyone asks, the reason I went with a glass-mount was simple: It was the easiest way for me to get a 'permenent' antenna onto my vehicle and the easiest to install (no drilling, no passing a wire through the body or firewall, etc.) The other reason I went with the glass mount is that I park in a garage and the glass mount allows me to keep the antenna mounted 24/7 (as opposed to my mag-mount which I have to take off when going into or out of the garage.)

 

[DaveInDenver]

Window tint and glass are physically indifferent for the antenna unless they're metallic imbedded or coated. They do this mostly to reduce radiated heat and I think to make the tint stronger or easier to install. If so then the antenna will almost definitely not couple through. You have to visualize these types of antennas like two antennas. One inside that is designed to be heard by or talk through the one on the outside. Ideally the two halves communicate with very little problem.

You tune it just like any other antenna, trimming the whip (or potentially adjusting a coil). With these glass-mount antennas I think an SWR meter is very important to know if the tint is affecting the coupling or not. If it's a metallic tint you are effectively doing the same as shorting the coax.

Keep in mind that you might hear stuff, even with a terrible antenna. Modern radios are very sensitive. Try just holding an antenna whip close to the SO239 on your radio, it'll probably receive just fine. That's because there's a strong enough field around the whip for the radio's detector. It might be a few S-unit below optimal, but it'll work. So that you can hear 147.225 or 145.145 here in town, which are normally S9++, at S8 (which is say 20dB lower than otherwise) doesn't mean it's working.

This is microvolts of received field. But flip the situation in reverse and transmit, now you have many orders more field strength feeding into a short. That your radio will definitely not like. What I'm leading up to is that just because you can hear with an antenna does not mean it's necessarily effective or safe to TX into. A random length of wire can accumulate enough RF energy to hear fine but unless the system is resonant it will not transmit.

I'm sorta busy the next couple of days, but if you can treat it gently until the weekend we can throw an antenna analyzer on the coax and see what it looks like.

 

[Martinjmpr]

Well, I can hit repeaters, I know that, because there are some repeaters programmed into my radio and I have been able to key the mike and get the "beep" acknowledgement tone. So a signal is definitely getting out, what I don't know is if it's an intelligible signal or if it's just breaking squelch.

 

[DaveInDenver]

Well, I can hit repeaters, I know that, because there are some repeaters programmed into my radio and I have been able to key the mike and get the "beep" acknowledgement tone. So a signal is definitely getting out, what I don't know is if it's an intelligible signal or if it's just breaking squelch.

That's still not indicative. People can hit most front range repeaters with 0.5W on an HT, so pumping 50W into a poor antenna will certainly work. Line of sight and elevation are our friends! The question is if you can hit the repeaters at minimum power. If so, then I would agree that the antenna is probably fine.

The analyzer will be helpful, plus I'll be heading home in probably 30~45 minutes. I can listen. I typically monitor 147.225, 145.310 and 449.825 for activity and they're usually busy. I dunno, 146.460 simplex and CCR (145.310/-0.6/123.0) starting at 1730?

 

[Martinjmpr]

I'm sorta busy the next couple of days, but if you can treat it gently until the weekend we can throw an antenna analyzer on the coax and see what it looks like.

I don't use it a lot during the week (well, it's in the 4runner and I've only been driving the 4runner yesterday and today because of the slick roads - I feel safer with 4500lb of steel around me than in my ~2500lb FWD-only DD.)

Unfortunately, I don't think I'll be available this weekend - Wife and I are going to the mountains, there's a camping trailer for sale that we might just buy!

Next week some time? What's your schedule like?

 

[DaveInDenver]

Next week could work. Won't know much until the week shakes out, but probably Mon or Tues is OK. Maybe on my home from work, 6:30ish?