Mag Mount Placement

[ctvanover]

I'm going to use a Sirio 5000 antenna along with a magnet mount from a Wilson 5000. My question is where would be the best place to put it on top of my '03 Silverado extended cab? In the middle of the cab, towards the back of the cab, or does it matter where? And one more question is the magnet all that I need for a ground?

Buck

 

[222DBFL]

Middle of the cab or about 1ft off the rear of the cab in the middle. The middle top of the cab is normally the best place, but some vehicles like the antenna a little back or forward of center of the top. Try the top center 1st and see what you get. The sirio antenna's normally don't need to be cut, but every install is different, I would make sure the whip is all the way down and start from there, with center of the roof.

 

[M0GVZ]

And one more question is the magnet all that I need for a ground?

Buck

I would argue that a magmount is a crap ground but on 11m they present less of a problem than they do on lower frequencies on the ham bands for low power. Magmounts use capacitive coupling to provide a ground and how well that works depends on the size of the magmount and the thickness of the metal you're sticking it to. Once you get above 50-100W then there starts to be issue caused by common mode, RF on the outside of the coax where we don't want it to be, causing distortion on the audio, mic bite from the RF and in some cases when it gets real bad, resetting of the CB when you key up. Adding ground straps to magmounts achieves nothing and the only real way to cure that is to get the drill out. But if you're sticking to relatively reasonable power then you'll be OK and in my opinion more than 100W is pointless anyway. I only run 4W here and have no issues getting 20 miles.

One thing that I would say does improve the situation is bonding, using flat braid straps to link body panels to the main body by bridging hinges of the hood, trunk lid/rear hatch and doors to improve conductivity for RF. Whilst DC conductivity between the body and the hood may be good it doesn't mean it is for RF. We want as much of the RF to flow over the body of the vehicle and bonding increases the ability for RF to do this. You can make your own from RG213 braid.

As you improve the RF conductivity between the panels you'll find the resonant point of the antenna lowers so you may find you need to retune it as the SWR dip will be at a lower frequency between starting and finishing the job. If you don't want to do a lot then concentrate on doing the horizontal panels. Even doing just the hood or trunk lid will see a difference. As long as the SWR is below around 1.5:1 on the frequencies you use, don't worry. Tuning for 1:1 is a waste of time. Looks good on a meter but makes little difference in reality.

More here:

Bonding

 

[222DBFL]

I would be careful using the wilson 5000 mount for the sirio antenna. JMO, the base load of the sirio is taller and the whip is longer than the wilson 5000, it may work, but I would have purchased the pl145 mag mount that sirio recommends using for that antenna. I bought both the 145 and 125 mag mounts, the 145 is 6" and the 125 is 5", and the 125 would not hold the weight of the pl5000 properly in my own experience. Just be careful with that wilson mount. I just am going by what was recommended to me when I purchased the antenna as well. When I asked if the 5" mag would work, they said to use the 6" mag mount due to the weight. Just some food for thought and I would hate to hear that you busted a window or worse by the mag mount coming off during high speed travel.

 

[The DB]

I've heard mixed reports about using the Wilson mounts for the Sirio antennas. That is where the thickness of the metal that M0GVZ mentioned comes into play. If the vehicle the magnet mount is on has thicker metal then the magnet will have a stronger hold to that metal.

In the case of most heavy duty pick-up trucks the Wilson magnet may well be able to support the Sirio antenna just fine.

However if you try and stick the magnet to the thin metal on the roof of an econo-box, well, good luck...

Same magnet, same antenna, different results.


The DB

 

[psycho]

The Wilson 1000/5000 magnet can't handle the Sirio 5000 monster.......you'll be picking it out of the bed every time you hit a tree limb. Go with a more powerful magnet mount.

 

[Lil'Yeshua]

Yesterday I smacked a low wire that was brought down low in account of the snow/sleet/freezing rain I had in my area. The wire was 8 feet off if the roadway. I couldn't slow down fast enough because if the slippery road conditions. My Sirio 145 mag mounted Sirio Performer PL5000 smacked the low lying wire and I heard the whip smack the rear luggage rack/roof area. I checked my antenna out at the first convenient stop. Because of the impact with the wire my antenna whip tilt section had tilted back 25 degrees from vertical after which I loosened the tightener and readjusted the whip back to vertical. As my roof being wet and it having extremely thin sheet metal,my 145 magmount was easy to tilt up from the roof. I think that the brief encounter with the low lying wire coupled with the possibility of my luggage rack front cross rail and my coax being zip tied to the cross rail kept my antenna from being completely knocked off of my vehicle.
Sirio did their homework when they made the tilt section a compression fit instead of making the mating surfaces toothed. That may have saved my antenna from any damage.

I would like to increase the holding power of my 145 magmount by glueing magnets on the bottom side of the car roof directly under the magmount itself but then again,I'm planning on doing a hardmount with a large support washer underneath and only tightening the antenna tilt set screw just enough to where the wind won't lay the antenna down and help negate any future strike damage

 

[ctvanover]

Yea I was kinda thinking about using the pl145 mag mount because it look bigger than the Wilson mag mount, I mean almost 6" of hold compared to 4 and 3/4ths!

 

[GnG8d]

One good thing about a magnet ...... you can experiment with locations!

 

[222DBFL]

There is definitely a difference, i just ordered another one myself, here are some photos. You know what the wilson mag mount looks like, here's the sirio

It is a much heavier magnet than the wilson and larger as well.

 

[ctvanover]

I got me one of the pl145 mag mounts off of Ebay. Shipping and all was $36 even. It should be here tomorrow. Upon further inspection of my antenna I don't think it's a Sirio 5000 but instead it's an Z-180 and the round blue sticker on the side has RM in it. I don't know if they're any good or not but I'm gonna try it out!

 

[222DBFL]

The z180 looks to be the pre pl5000 model, from all readings I have seen, I think you will be happy with the setup. Keep us posted and good luck with the install, hope you get it all sorted out. God bless.

 

[ctvanover]

A quick question? Would a ground plane for a mag mount like the one in this pic help or hurt or just make it look different, lol?

 

[W5LZ]

If you call that "groughplane" what it is instead of something it isn't (a top-hat/capacitive hat) then if your antenna is too short to start with it would be a benefit. If it isn't too short to start with then no, it won't help anything.
That is not a "groundplane" in any sense of the word. A snake may look like a stick, but I know which one I would pick up and which one I wouldn't...
- 'Doc

 

[M0GVZ]

A quick question? Would a ground plane for a mag mount like the one in this pic help or hurt or just make it look different, lol?

Complete and utter waste of time. The only thing they do is empty the wallets of the gullible.