Whiskey363

Ended up measuring the Tram antenna today. Following the video Steve posted, I trimmed 5/8 inch off the first section, and about 1/4 to 3/8 of the next two sections. I have not got a chance to test it yet, but for what is worth that is how far off it was. On a side note, DX engineering is sending a new Comet CA-712EFC as I have 1.5 SWR on 462MHz and 2.5 SWR on 467MHz, and the antenna cannot be trimmed. Reading the reviews on this antenna it is hit or miss how it is cut, but the good ones are supposed to be great. We shall see.

GMRS has 22 Simplex channels (Radio to Radio) 1-22. It has 8 repeater channels RP15-Rp22. The first repeater channel available is 462.5500. This chart is helpful to be able to see it.

I will be checking the old antenna, as I will be using on a portable repeater. I will update what the length measurements were when I do that.

It is a new antenna, and of course I should of, but no I did not. It is in the 20's and windy, just wanted to get it done!

Installed 75 feet of LMR400, N Male One End, DXE PL259 with a 10 foot tall Comet 9dB antenna mounted on a 10 foot pole. As Steve mentioned would likely happen, SWR went up on the 467MHz frequencies to 2.3-2.5. I did a radio check with the repeater 15 miles away, and I got an immediate response. They could hear me with some static. Pretty impressed with 15 miles in the city with buildings and hilly terrain. I wanted to check the SWR at the antenna, but I could not figure out a way to safely do it. Either way I can hear a significant higher amount of traffic, and it is much clearer. don't know if the SWR is a concern, but at least it is clear. Thank you to everyone for your help!

Steve, that is the plan, I am just waiting for the coax so I don't have to take down the antenna twice.

That's the plan, just waiting for the new coax!

Great concise video, thank you for sharing. Could have saved the $40 and cut it to 465 from the start.

Great idea, thank you!

Being new to this I paid the seller I purchased from to trim it to "GMRS frequencies" so I would not have to deal with this, but the articles I read stated what you did. That a higher SWR on lower frequencies meant the antenna was to short and a higher SWR on higher frequencies meant the antenna was to long. When I get the new coax I suppose I will have to study how to trim the antenna, and by how much.

Thank you for the link. Are you satisfied with the performance of the antenna?

Headed to work, but thank you for your insight. Will certainly continue to research before I pull the trigger on the final coax and antenna.

I'm using the Tram 1486, but was thinking of switching to the Comet CA-712EFC 460-470MHz 9 dBi Gain Base/Repeater Antenna when they come back in stock.

Steve, With that being said what would you estimate the actual SWR reading is? From my understanding anything over 2 can damage the radio. Or is the incorrect SWR reading at the base of the radio taken into account with the 2 or lower number?

That is something I was completely unaware of. Thank you for informing me of that. At 1.8 I really can't afford for it to be any higher. Would you recommend I do not upgrade the coax? I was under the assumption this would lower the SWR as well. Thank you for your excellent, easy to understand explanation.