7" mag mount or drill a hole ?

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ghost123uk
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7" mag mount or drill a hole ?

Post by ghost123uk »

I have been into CB since the early AM days, I even owned the local CB / Electronics shop for around 18 years, but I have never done a proper test of this =

Assuming your average 1/4 wave car CB aerial, used in the centre of a car roof.
Do you think a 7" mag-mount gives similar performance to a proper fixed (drill a hole) mounting?
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Re: 7" mag mount or drill a hole ?

Post by 26TM5890 »

personally i think that a proper fixed mounting is better simple due to proper connected to the metal of the vehicle. this is just assuming as haven't tested my self
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Re: 7" mag mount or drill a hole ?

Post by Hair Bear »

First thought is access to the underside of the roof to attach the coax and have regular access for maintenance. How easy is it to reach over the top of the roof to unscrew it when you need to? How confident are you to get the hole in the right place first time?
What sort of antenna do you intend to use? A mag will knock off for a low branch or if you forget when there's a height barrier. A drill through will benefit from a spring.

I wanted something a little covert, so I went with a drilled mount. There's a courtesy light in the middle of the car so popping that out to get to the mount is easy. The antenna is one of a pair of center loaded 'twin truckers' which isn't particularly long and doesn't look like a cb antenna. I like the subtle approach. The result works very well and looks more 'business comms' rather than cb. My other car came to me with an early mobile phone antenna in the roof. No-brainer on that one, make the hole bigger and fit the other half of the trucker set.
For my liking, having the confidence that it's there and it's going to work when I need it beats the slight uncertainty of 'how many times has the coax been shut in the door', or 'how much moisture has got into the mag joint on the roof?'. Also less of the boy racer image.
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Re: 7" mag mount or drill a hole ?

Post by ghost123uk »

Cheers for the input Hair Bear.

Over the (many) years, I have used both types of mounting on various cars and VW camper vans.

I was more curious about the RF performance differences between a 7" mag base and a proper earthed drilled mount.

I know that I, and I bet many others, would guess that a proper mount will work a bit better than a mag mount, but I just wondered if there is any factual basis on making that assumption..............
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Re: 7" mag mount or drill a hole ?

Post by Hair Bear »

Ah, sorry, just reread your original post. On that basis I can't help you, previously I was using a stick-on-glass which sort of worked but you can guess the comparison compared to that!!!
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Re: 7" mag mount or drill a hole ?

Post by Ant »

I always take the compromise and use a mag mount, no antenna is worth drilling a hole into a car for, once you've drilled the hole, there's no going back and the car is un-sellable.
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Re: 7" mag mount or drill a hole ?

Post by ghost123uk »

Ant wrote: 09 Nov 2021, 18:04 .....................no antenna is worth drilling a hole into a car for, once you've drilled the hole, there's no going back and the car is un-sellable.
Not sure about the drilling of a hole makes the car un-sellable, mind you, mine is a VW T4 (20 year old, but tidy) camper van, so maybe it is not such a big deal compared to a modern £30K + car.

However, the question still remains = is a "proper" mount any better performing than a good quality 7" mag mount...............
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Re: 7" mag mount or drill a hole ?

Post by Ant »

ghost123uk wrote: 09 Nov 2021, 18:23
Ant wrote: 09 Nov 2021, 18:04 .....................no antenna is worth drilling a hole into a car for, once you've drilled the hole, there's no going back and the car is un-sellable.
Not sure about the drilling of a hole makes the car un-sellable, mind you, mine is a VW T4 (20 year old, but tidy) camper van, so maybe it is not such a big deal compared to a modern £30K + car.

However, the question still remains = is a "proper" mount any better performing than a good quality 7" mag mount...............
I wouldn't buy an 18 month old E Class if someone drilled a hole in it....in fact I wouldn't even buy a 5 year old Mondeo if someone drilled a hole in it.
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Re: 7" mag mount or drill a hole ?

Post by ChubbyChops »

I drilled the front wing on my camper as there's no other realistic option for a usable aerial.
Obviously it's directional due to location but swr is very low (much lower than I've ever seen on a mag mount), so I assume it's a better and more effective method.
Not something I can really prove or quantify though.
I'm also not bothered about a hole in the wing as every car I had up to a few years ago had a hole for an entertainment radio aerial and as it's mine and I'm not planning on selling it, it's unlikely to matter.
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Re: 7" mag mount or drill a hole ?

Post by original45 »

I can't drill holes in my car roofs the Mrs would kill me. I can only imagine using the largest dia and best quality strongest mag base you could find may help.
I also think on some the rubber base protective pad is far too thick surely can't help

Had a couple of the older 7" turbo jobs, both have the grounding wire riveted to metal mag base.both corroded and loose.I removed cleaned and used brass bolt instead. Protected from elements after.
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Re: 7" mag mount or drill a hole ?

Post by The Collector »

I drilled a hole in my Renault Espace's roof a few years back. It didn't devalue it. Renault Espace translates into English as "French heap of sh**" anyway ;)

I put pictures on here at the time which you may be able to search for.

The hole is near the tailgate as it'd be almost impossible to reach the centre of the roof without using steps...and I'm 6ft 4". I could then reach easily inside the roof lining for connection/sealing purposes.

I've got an 18" handheld-type thin rubber duck aerial on an SO-type mount, but it's also got a little modified dummy "shark's fin" covering the base so it disguises it further as well as helping to waterproof it. I can take the little aerial off as well as the shark's fin and pop a bigger aerial on in 20 seconds flat if the need be...which is probably going to be never :)
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Re: 7" mag mount or drill a hole ?

Post by astradyne »

I'd opt for the magmount. You can always take a feed from the outer braid of the co-ax somewhere inside the car and attach that to a good earthing point somewhere.
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Re: 7" mag mount or drill a hole ?

Post by Admiral »

In theory, no, because the capacitive coupling of a magmount isn't as great for HF as a direct metal to metal contact to the ground plane. In practice, so long as the vswr is identical then the performance difference will be negligible.
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