N9tax

[W1JOP]

just recently mounted this antenna outdoor with a fiber glass mast at 18feet it’s the dual band VHFUHF version my SWR it’s below a 1.5 in the 146 MHz and lower portion of the band once I get above 147 MHz the SWR creeps up to 2.0 it’s not really a big deal to me since I don’t use a lot of repeaters on 147 MHz but it would be nice if I could get it lower in that region

Using an icom 9700 so obviously even though an SWR of two would not likely cause damage because of the expense of the radio, I’d rather get the 147 MHz down to 1.5 or so


Any recommendations would be helpful thanks

 

[K4EET]

just recently mounted this antenna outdoor with a fiber glass mast at 18feet it’s the dual band VHFUHF version my SWR it’s below a 1.5 in the 146 MHz and lower portion of the band once I get above 147 MHz the SWR creeps up to 2.0 it’s not really a big deal to me since I don’t use a lot of repeaters on 147 MHz but it would be nice if I could get it lower in that region

Using an icom 9700 so obviously even though an SWR of two would not likely cause damage because of the expense of the radio, I’d rather get the 147 MHz down to 1.5 or so


Any recommendations would be helpful thanks

You didn't mention at what frequencies you are making those SWR measurements but the difference between 1.5:1 in the lower 146 MHz portion where the transmit frequencies are and 2.0:1 in the upper 147 MHz portion where the transmit frequencies are would not be unusual. That said, SWR can be affected by nearby objects. Have you tried relocating the 18 foot fiberglass mast to see if the SWR changes? Also, you need to make sure that the mast is pure fiberglass with no PVC or metal included. According to the designer in this video at the 25 minute 30 second mark, PVC does affect the antenna's characteristics. You could try hanging the antenna with Dacron rope in "free space" away from the fiberglass mast to see if the SWR changes. There is not much you can do with the tuning other than to try some different deployment scenarios to see how the SWR curve might change.

 

[W1JOP]

so more or less this would be pretty within normal operation of this style of Antenna, 146.790 its pretty much 1.1- 1.3 it jumps close to 2 when I get up to 147.345.

This at the moment is a trial set up to see it the antenna performs better out doors, and it does I have it on temporary COAX RG58 at 50feet so that prob has something to do with it to, I am going to get LMR400 Ultra-flex when I have the funds, I am slightly HOA so I have to find a coax that has good performance but can be snaked around siding and such

 

[K4EET]

so more or less this would be pretty within normal operation of this style of Antenna, 146.790 its pretty much 1.1- 1.3 it jumps close to 2 when I get up to 147.345. <snip>

So you are transmitting at 146.19 MHz and 147.945 MHz. You still might try different mounting locations and/or methods to see if your SWR readings change. If the 19/79 repeater is your preferred machine, you are golden at 1.1:1 SWR.

 

[AK9R]

An SWR of 2:1 is not the end of the world.

A J-pole antenna is an end-fed half-wave. As an end-fed, the feed point at the end of the antenna has a high impedance. The bottom third of an J-pole is a quarter-wave matching transformer so you can feed the antenna with a 50 ohm feedline. That transformer is unshielded, so nearby ferrous objects can upset the magnetic field. It's always a good idea to keep a J-pole away from ferrous objects.