Antenna tuning question

[tdukes]

I searched the forum but couldn't find what I was looking for.

Just got a Tram 1486 antenna and it needs to be tuned. Do I tune it for 462 or 467, or maybe in the middle, 465?

Thanks!!

[SteveShannon]

Just now, tdukes said:

I searched the forum but couldn't find what I was looking for.

Just got a Tram 1486 antenna and it needs to be tuned. Do I tune it for 462 or 467, or maybe in the middle, 465?

Thanks!!

You’re best off tuning it for your transmission frequency. If that is strictly in the 467 range then tune to that. If it is divided between 467 and 462 then tuning to 465 works. 

[tdukes]

I'm on a repeater and was going to go with 465 but since SWR is for the TX, I wasn't sure. Didn't want to start cutting if I wasn't sure.

Thanks!!

[marcspaz]

 

Never mind.  I'm a dumbass.

-----------------------------

I have a question... why are you going to try to tuning it?  It's a stacked 5 phase element high gain antenna with the center frequency being very close to GMRS frequencies.

 

Due to being a stacked phased element antenna (5-1/2l), if you cut the top or bottom, you are only adjusting one element and throwing the phasing completely out of whack, causing massive issues with receive and transmit, regardless of what the SWR meter says.  You can't even adjust all 5 elements because the LC network of the antenna is tuned for factory resonance. 

 

I would just leave it alone.

Edited August 12, 2022 by marcspaz
I'm dumb.

[OffRoaderX]

I have a Tram 1486 and i tuned mine because the instructions said I had to -  following the instructions to cut both the top and bottom sections, I tuned it to 467.700 because it is for a repeater... But when I checked the tune on 462.700, the SWR was still a very low -  dont remember exactly what it was, but under 3:1.

[marcspaz]

6 minutes ago, OffRoaderX said:

i tuned mine because the instructions said I had to

I have never owned one... so I did not know this.  I am really surprised they have people adjusting them... unless the target customer is more technical rather than Joe Q. Homeowner. 

[aa7jc]

I just got a 1486 last week and I cut it for 462 using a nano-VNA. 
The sections that need be to cut look like they are brass.  I cut them accurate and clean just using my scroll saw

So far performance is pretty good.  The chart was pretty accurate for me.. In the end my lengths were exactly what the chart suggested for 462. 
I have heard that many people found that the chart was off for them so be careful not to cut too short! 
It is easy to be off by a mm or so depending how you hold your ruler to the base of the coils. I measured with the butt of my zero clearance ruler touching the base of the coil.

 

.

[WRAM370]

I also found the cutting chart to be pretty close, and I made a number of small cuts on my 1486 until I achieved the best results. And as  stated above, I aimed for the lowest SWR at the transmit frequency. I found the uncut Tram 1486 to be resonant around 420 mHz out of the package, so it needs to be cut for the appropriate frequency.

I would also like to offer an observation about the Tram 1486. I had run a Comet CA-712EFC antenna, which is 10’ tall, on my repeater for the past couple of years, and it worked ok. I had very good swr measurements, fed it with 1/2” hardline, but my coverage was spotty due to my location. I live in an area that has rolling hills, with elevation changes of a couple hundred feet +/- within a mile or so of my location. I often say it is like living on a rollercoaster around here.

Earlier this year, I put the Tram 1486 on the repeater, and it made a significant difference in my specific case. The Tram antenna seems to have a lower angle of take off, and/or a more downward radiation pattern. Using the Tram 1486, many of the RF “holes” that I had in my local coverage area were now filled in. I now have very consistent coverage within the 3-5 mile radius of my repeater, where I previously had a lot of holes in that same radius, with the Comet CA-712EFC.

I have seen similar size antennas recommended on the forum, and they are no doubt of higher quality compared to the Tram 1486. It just so happened that I had the 1486 sitting in it’s packaging from when I bought it a number of years  ago, so it was already here (and much cheaper when I bought it, versus today’s price).

Just wanted to pass on my experience with this antenna, versus a more expensive and larger antenna. For those looking to install a repeater or an antenna for your base radio, carefully consider your terrain. In my case, “less” turned out to be “more”.

 

[KAF6045]

There is a 3dB difference in the listed gains for the antennas. The CA-712 at 9dB will have a thinner pattern extending out to the sides further than the 6dB 1486, which will have a pattern with "fatter" lobes going up and down more, but with less distance overall.