Tuning a pre-tuned antenna

[WSBV579]

I've got a Nagoya UT-72 dual band antenna on my Jeep. I've just cut it down to tune for GMRS. I've got Ch19 (my main simplex channel) from 1.75 swr down to 1.42. I did get it to 1.19, trimmed a touch more to improve repeater channels, and ch19 went up to 1.42...so I assume I'm done cutting at that point. That leaves the repeater channels around 1.98...it was 3.10 before I started trimming, yikes!

First question...are those acceptable ranges, 1.42 simplex, 1.98 repeater?

Second question concerns my base antenna. I've got a Tram 1477, pre-tuned dual band. I checked the swr on ch19 and it's at 2.18. and repeater channels are around 1.50. Are those acceptable ranges, or should I try to figure out how to tune it...and if so, do I trim or lengthen?

Last question. Other than trimming/lengthening the antenna, is there anything else I can do to improve my swr?

[Sshannon]

6 minutes ago, WSBV579 said:

First question...are those acceptable ranges, 1.42 simplex, 1.98 repeater?

They are, but some people would try to tune them. I think I would not. 

[Sshannon]

1 minute ago, WSBV579 said:

Second question concerns my base antenna. I've got a Tram 1477, pre-tuned dual band. I checked the swr on ch19 and it's at 2.18. and repeater channels are around 1.50. Are those acceptable ranges, or should I try to figure out how to tune it...and if so, do I trim or lengthen?

Trimming would make the 462 MHz channels higher SWR because it’s already higher SWR than the higher frequencies.
Without sweeping it using an antenna analyzer it’s difficult to know which way to go for the repeater channels: is the bottom of the dip left or right of the repeater channel you looked at?.  

[WSBV579]

10 minutes ago, Sshannon said:

Trimming would make the 462 MHz channels higher SWR because it’s already higher SWR than the higher frequencies.
Without sweeping it using an antenna analyzer it’s difficult to know which way to go for the repeater channels: is the bottom of the dip left or right of the repeater channel you looked at?.  

Going to 470 MHz, the swr got even better. So I assume I would need to lengthen to make my ch19 better. I'm taking the antenna down on Monday to add a 10ft extension, I'll look and see if lengthening is an option.

As it sits, is 2.18 on ch19 and 1.50 on repeater channels acceptable? If so, I may not even bother tuning any further.

[Sshannon]

3 hours ago, WSBV579 said:

Going to 470 MHz, the swr got even better. So I assume I would need to lengthen to make my ch19 better. I'm taking the antenna down on Monday to add a 10ft extension, I'll look and see if lengthening is an option.

As it sits, is 2.18 on ch19 and 1.50 on repeater channels acceptable? If so, I may not even bother tuning any further.

2.18:1 is acceptable, but not great; I’ve used worse. 

1.50:1 is just fine. I probably would not do much. 
If 470 MHz is even better SWR then the element is slightly too short. 

[WSBV579]

13 minutes ago, Sshannon said:

2.18:1 is acceptable, but not great; I’ve used worse. 

1.50:1 is just fine. I probably would not do much. 
If 470 MHz is even better SWR then the element is slightly too short. 

Alright, if I can figure out how to lengthen it...like loosen a set screw or something...then I'll see if I can improve it. If not, I'll just leave it as it. 

Appreciate the help.