some quick help please

You should see an increase on both.

 

The 3' antennas are basicly junk, go with 48" minimum. I use Francis 6' and have been really happy with them.

 

Get rid of the co-phased coax and get 18 ft coax put a 4 1/2 ft francis antenna on passenger side. Pretuned antenna no need to mess with it...thats what I use get out all over the place...no worries.

 

Co-phasing ...

 

Even as close as 4 ft apart two equal phased verticals do squeeze some gain toward front and back vs side to side. At 8 ft. it's almost 3 dBi front and back vs 0.7 dBi side to side. Max gain is at about 7 dBi. at ~286 inches apart. Actual optimum is probably near 18 ft.

These are dipoles in free space so one alone gives ~2.2 dBi so at 8 ft apart you only stand to gain about a dB maybe less due to real world losses in the harness.
I personally never used the company provided harness and antennas and used a straight run to a single ~4 foot fiberglass antenna on a bolt-to-the-mirror mount. Just like slowride suggested above only I don't trust pre-tuned and would check the SWR any way.

I just never figured whole 2 antenna system was worth the trouble of uninspect-able built in coax and more difficult SWR adjustment.

 

One of these days I'll give up on this but, 18 ft of coax is not a myth! Francis used to state right on the package to use 18ft. (I think it was Francis) It is also obvious many of you don't do any/many installs! Coax length, if everything is perfect, does not matter, true. But there are few perfect situations on modern day trucks!!! On a Freightliner Cascadia, using the walcott perch mount on the mirror and a 5x5 Francis, the SWR changes drastically when switching from different lengths of coax. Guess which one gives you the lowest SWR and makes it possible to use your radio???? I have tried 9, 12, and 18 foot lengths. (about 9ft would be the length to use if everything was perfect) Only the 18ft length gets the SWR down below 2:1. All the other lengths give you a 3:1 or worse! So when you spout that length doesn't make a difference......maybe not in the text book, but in the real world it can mean the difference in having a safe SWR or not!! (I know it doesn't fix the problem)

I can prove this and have many times because I've done it many times! And AB7IF explained why this is so scientifically in another thread awhile back........Now most of you stating this have way more technical knowledge than me, and maybe on the installs you have done you had a good rf ground and everything was good enough. But, on these new trucks, and new pick-ups for that matter, that ain't the case. Different lengths of coax do help overcome (I know it doesn't fix the problem) a high SWR problem.

When it is midnight and I'm moving in to a truck and need to get to bed so I can take off the next day, I don't have time to "fix the problem"! But I can switch out lengths of coax quickly so at least I'll have a radio I can safely talk on!!

Note to CJ: you can do three pages on this if you want to.....I don't waste my time on your posts, even if they are only one sentence long......FWIW.

 

The reason you need 18 ft with the francis is because the antenna is not adjustable.

With an antenna that is adjustable coax length doesn't matter because you can adjust the antenna length

 

I've read what Francis wrote and disagree.

A much better approach would be to use a antenna tuner if you don't have the time to do it right. A small tuner can be built or purchase for very little money.

I've also read what AB7IF wrote and what he based his opinion on what he did not explain was it was a special case.

Leon
(kc0iv)