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K40 Antenna Rant

Mudfoot

Mudfoot

Elmer
Jun 17, 2009
10,928
6,299
698
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Southeast Ohio
I got my K40 today. It claims to be a universal mount, either trunk lip or thru the roof. Instuctions for roof mounting simply tells you to mount the plastic base to top of roof and tighten the set screw from the inside. There is no gasket (foam donut) included, nor is it mentioned anywhere in the instructions that you need one.

https://dl.dropbox.com/u/39278999/NewDoc.pdf

There is a rubber gasket for trunk lip mounting, but it's insufficient for roof mounting.

Called K40 tech support, talked to two different guys. I ain't kidding. neither one had any technical knowledge at all.

Copper sells the donut for .99 cents, but wants around $12.00 shipping. Solid Signal, which is where I bought the antenna wants close to $15.00 total for a 1/10 of a penny foam donut.

The damn donut should come with the antenna!

K40 has obviously went to shit.

The moral of my story...Stick with Wilson Roof or some other proven design.
 

Just a 'heads up' .. .

I think the disc capacitor in the base of the K-40 is a .47mfd. You might check it to be sure. Chance are, you are going to replace it if you put more than 200 watts into that antenna. Personal experience - twice. You will know that you popped it if the SWR goes crappy on you. Perhaps try using a .47mfd disc with a 1.5kv rating; maybe that will help. Maybe not; gave away the two K-40's I had before I modded it like that. Mine were mag mounts; never mounted it with a surface mount.

Just saying . . .
 
The only practical mounting solution for this antenna is magnet or trunk lip. Do not even mess with roof mounting. It is totally junk when attempting to roof mount.

They are sold by a company that has terrible technical support. I could go into detail as to why it's a POS, but have better things to do with my time.

Roof mount fail.
 
I installed hundreds of the K-40's back in the eighties! I worked for a custom van company. The roof mount seal did not come with the antennas, we had to order the seals. They are a good antenna for running up and down the road, and for the fact that you can remove it with a twist of the wrist.

For the avid keyer I'd leave it in the garage!
 
Interestingly I stumbled on this thread. I have a K40 trunk lip mount a friend gave to me. I'd like to use it on my pick up truck.

I wanted to roof mount it but I suppose this isn't such a great idea?

Also what's with the capacitor inside the antenna?
 
Turbo T said:
Interestingly I stumbled on this thread. I have a K40 trunk lip mount a friend gave to me. I'd like to use it on my pick up truck.

I wanted to roof mount it but I suppose this isn't such a great idea?

Also what's with the capacitor inside the antenna?
Click to expand...

What is wrong with the roof mount?

The capacitor is there to help with tuning the antenna. Its function is to attempt to be near resonance while also having a low SWR rating at the same time.

If you have the ability to or know someone who does, I would still tune to resonance rather then low SWR.


The DB
 
I have had two K40's over the years, plus my dad had one on his old Rambler for a long time. All were trunk lip mounts. Never had any problems with any of them. The K40's roof mount scheme is just plain ignorant. One allen set screw to hold it down from below the roof line = junk. Total failure and not worth the effort.
 
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K40 best mobile antenna there is

I have had two k40 antennas on two different cars and both of them were roof mounted. The reason they don't put the weather doughnut in with the antenna is the antenna is a three way mount by the choice of the user. Very few people roof mount these antennas through the roof of the vehicle. It would not be cost effective for the company to provide these weather seals when only one out of a hundred people will use it. I had to buy mine as an add on to my antenna for roof mounting. Not a big deal and not something that requires any negative feedback on a great antenna. If installed correctly this antenna will provide a very clean and professional look and last many many years. if the weather doughnut only cost a few bucks but the shipping cost twelve, so what it's worth fifteen dollars give or take a few. Or order something else to go with it I'm sure your shipping will not change. you're throwing off on a very good antenna because you don't want to spend a few dollars for a part that is needed but keep in mind is an extra item. K40 doesn't owe you this part by any means. Now, the one thing that I am going to say negative about the company is when you buy a new k40 they do not mention anywhere in their instructions that you even need to purchase the weather doughnut. Why I don't know. The reason I knew about the weather doughnut is I've bought k40 antennas since the early 1980's. I already had the knowledge that this part does exist. With that said when I went looking for a k40 this time I started looking for the doughnut as well. I bought several just to have on hand. And yes I paid about 8.50 shipping on a two dollar part. Wasn't a big deal. I was glad to do it because I needed it. The k40 antenna is ten times better than a Wilson. At least when you take off the k40 the swr stays the same when you put the k40 back on unlike the Wilson.
 
A Unibit drill bit and a desire not to screw up along with some primer paint,top coat,star washer and a doughnut gasket of sorts will make for a pretty clean hard mount. I bought the hard mount kit for my Sirio Performer PL5000. Just gotta find my bigger Unibit
 
You also need a spark gap if using power. Raise the antenna off of the bottom of the base by lifting it out at least 1/4"-1/2". This may require some cutting to the antenna as it is too long for cb frequencies. This should eliminate the blown capacitor that is located inside.
 

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