4 SWR reading on my new TRAM 1486-Help

[Arawak]

I installed a new TRAM 1486 Antenna and tuned it to 462MHz per their reference cutting chart. When I transmit with my Midland MXT400 the SWR meter registers 4 in the scale. Did I cut it wrong for GMRS? L1 (444mm), L2 (334mm), L3 (368mm)

[tweiss3]

I don't think that radio has an SWR meter. It appears the "meter" on the right side of the screen is received signal strength, and power out on transmit. A 4 would probably indicate you have it set on medium power?

[Arawak]

I have a jetsream JTW270 SWR Power Meter connected to the antenna cable and that is where the meter reads 4 SWR. I does read 4 only on channels 15-22. On channels 1-7 the SWR reading is below 1.

[tweiss3]

39 minutes ago, Arawak said:

I have a jetsream JTW270 SWR Power Meter connected to the antenna cable and that is where the meter reads 4 SWR. I does read 4 only on channels 15-22. On channels 1-7 the SWR reading is below 1.

Are you using the repeater channels for 15-22 (467MHz), or the simplex (talkaround)?

[mbrun]

I have a jetsream JTW270 SWR Power Meter connected to the antenna cable and that is where the meter reads 4 SWR. I does read 4 only on channels 15-22. On channels 1-7 the SWR reading is below 1.

Assuming the meter is working correctly, and installed in circuit correctly then there is a problem with your antenna system (feed-line, adapters and antenna). Now begins the process of elimination. You may wish to try your measurements again using the shortest possible cable length and different adapters as you have them available to see if results change.

I am not a fan of cut-by-chart trimming of antennas. When an antenna is known to be long for its intended purpose, I prefer to trim a little and measure, then repeat as necessary so as to sneak up on the target value. Doing so helps you know where you are getting close (because SWR gets better with each snip) but also when you have gone too far (because SWR starts to rise). Be aware that at high frequencies, minute length changes can cause big changes.

It is possible that you may already snipped it too much, but also that you have not snipped it enough. Further, If you are testing using repeater input frequencies (467 MHz range) and the antenna is actually tuned for 462 MHz range, then the 467 numbers will appear higher than the 462 numbers.

Snipping of course should only be done on a basic antenna, or one that is, by design, intended for sniping and/or you have advanced knowledge antenna designs. I don’t own your specific antenna, so I cannot cannot from experience comment if it is designed for cutting or not.

For what is is worth, there no such thing as an SWR of less than 1. The first number is always 1 or greater, and the second number is always 1. Collectively they would appear as follows: 1.5:1, 1:1, 1.15:1, 4.7:1, etc. So .8:1, 0.5:1, 1.25:2 are all examples of invalid SWR values.

Hope there is a little nugget of assistance in there.


Michael
WRHS965
KE8PLM

[tweiss3]

I can't find the documentation for bandwidth at tuned frequency; however, you should have tuned for 465Mhz, which would cover 462 simplex and 467 repeater inputs. I know it sounds different, but when you tune for 462 to be the lowest SWR, 467 ends up out of the curve with rising SWR.

[BoxCar]

The published bandwidth for the 1486 is 10 MHz. The Tram 1485 has 5dBd gain with a 20 MHz bandwidth and is pretuned to 460 MHz.

[Arawak]

Thank you for all of your responses. I went back and re-tuned the antenna for 465MHz and re-checked the reading on the SWR meter. No change. At this point my assumption is that there may be something wrong with the coax cable or the antenna itself. I'll do some checking with my multi-meter to see if the coax cable is broken on the inside or of there is an issue with the connectors. I did nome reading and there seems to be two views on grounding or not grounding the antenna. At this point my antenna is not grounded but I'm not sure if that by itself will have any impact on the SWR reading.   Will see how it goes.

[axorlov]

JTW270 is a cross-needle meter. Channels 15-22 are 462.xxx0, do you push full 50W on them? Do you set the power range correctly on the meter (15W vs 150W)? When you say SWR is 4, what does your meter show for forward and reflected power? Is your forward power about you'd expect? Can you repeat the test with different power from MTX400? Do you have dummy load (UHF-rated) to verify your coax?

[axorlov]

I will elaborate a bit more. Your problem, Arawak, is clearly related to power. The channel 3 (462.6125 MHz), according to your post, shows SWR below 1 (which is not possible, let's say below 1.1), while the channels 17 and 18 (462.600 MHz and 462.625 MHz) show SWR 4. That makes ZERO sense since chan 3 is between the 17 and 18.

Possible explanations are: 1) wrong measurement setup (likely); 2) antenna not rated for full power (I did not read the spec); 3) coax and connectors working fine at 15W but crapping out at 50W (less likely).

[Citizen]

I too have the Tram 1486 antenna, and I have the cutting chart that came with it (it says "Chart #64" from Tram-Browning, Inc.). 

Your cuttings for 462 appear to be correct.

The chart does not list 465 specifically, but it does have 464 and 466, so I guess you/we will have to extrapolate if you want 465.  Anyway here are the cutting lengths for the three sections (labeled L1, L2 and L3).  NOTE: L1 is the section closest to the base (bottom), L2 is the middle section, L3 is the top.

464 (claimed SWR < 1.5:1, band width 449.8 - 472.6)

• L1: 17 21/64"  440mm
• L2  13 5/64"  332mm
• L3  14 29/64"  367mm

466 (claimed SWR < 1.5:1, band width 451.3 - 473.1)

• L1: 17 13/64"  437mm
• L2  13 1/32"  331mm
• L3  14 13/32"  366mm

To be safe, I first cut mine for 458mHz (stated bandwidth 444.0 - 468.5), which seemed ok, but....  I then got brave, and then trimmed for 462mHz (stated bandwidth 447.6 - 471.5), and this is where I still have it today, as it easily covers GMRS.  Have not trimmed further as this last trim seems to work well for me for now, as I can hit my favorite repeater, which is 15.5 miles away LOS.

Hope this helps.

Thomas

...

 

[Arawak]

Greetings to all that took the time to comment...appreciated. I had some time today to go and take a look at the problem again. I disconnected the antenna and checked the 50Ft coax cable for any issues. Used a multimeter to check for conductivity. The cable appears to be ok with a reading of 3.0 ohms tip-to-tip so I assume is not broken. Attached are some picks showing you the setup (image 5&6 antenna outside), (image 3 radio transmitting on channel 15-notice power meter on radio and reading on SWR meter), (image 0 radio transmitting on channel 4-notice power meter on radio and reading on SWR meter). I can't see what may have been wrong but it looks like the unit is operating fine now. I'll start using my mobile units now to see what kind of range I get from home. Next project will be to find if there are any nearby repeaters and see if I can set my radios up to work through them. Thank you all who took the time to read and comment. Merry Christmas.

[axorlov]

Both measurements show very low SWR. The chan 15 shows 35W forward power, that is expected and close to claimed 40W. Second is just tad below 5W. The 15W-150W switch on the face of the of the SWR meter seems to be depressed for both measurements. Looks like depressed is for 150W range (based on 35W reading for 462.550MHz)?  Make sure you have it in correct position for 40W and for 5W readings. You will have more precision in 15W range for the low power measurements.

Other than that, everything is nice and dandy. What cable do you use? 50 feet of RG-58U will give you a low SWR reading, and a lot of loss.

[Arawak]

I purchased a RG-58 Coax Cable, 50ft long from the GMRS website. It was listed with the following description: "Retevis RG-58 Coax Cable 50-Ohm 50 Ft". On a separate note, I did find out that the Midland MXT 400 microphone cable is kind of weak in the connector when you pull and stretch the microphone cable. You need to make sure the cable connector is set in firmly or you will not be able to transmit. Since I'm using this radio at home I'm going to see if there is a desk top microphone that can be used with this radio and that probably will be a better solution. Midland probably should look at making the connector better. I have another MXT 400 radio on my wife's car and she told me had a similar issue if she handed the microphone to my son riding on the passenger seat.

[gortex2]

RG58 made by beldon is 6.5 db loss at 100' on UHF..... If you got cheap cable you could have 4-5db of loss just before the antenna. Thats over half your power. 

[Luish19779]

Tram Antennas Chart.
https://images.carid.com/tram/items/pdf/tram-product-catalog.pdf

[WRTI255]

On 11/11/2021 at 12:38 PM, Arawak said:

I installed a new TRAM 1486 Antenna and tuned it to 462MHz per their reference cutting chart. When I transmit with my Midland MXT400 the SWR meter registers 4 in the scale. Did I cut it wrong for GMRS? L1 (444mm), L2 (334mm), L3 (368mm)

1st of all they put out different cutting charts,mine is #64 and i cut it to456 then to 458 which gives me 1.5 on my workman meter running around 50 feet total with 25 feet in the air. i have tws600 i got for nothing but i need one connector and its 35.00 plus shipping. go figure. i would cut to 462 but scared as heck to do it im thinking lmr400 and 50 feet for 44.95 ebay free shipping. running motorola repeater at home,ruggedradio in truck. private

[WRZI712]

On 12/17/2021 at 8:44 AM, Arawak said:

I purchased a RG-58 Coax Cable, 50ft long from the GMRS website. It was listed with the following description: "Retevis RG-58 Coax Cable 50-Ohm 50 Ft". On a separate note, I did find out that the Midland MXT 400 microphone cable is kind of weak in the connector when you pull and stretch the microphone cable. You need to make sure the cable connector is set in firmly or you will not be able to transmit. Since I'm using this radio at home I'm going to see if there is a desk top microphone that can be used with this radio and that probably will be a better solution. Midland probably should look at making the connector better. I have another MXT 400 radio on my wife's car and she told me had a similar issue if she handed the microphone to my son riding on the passenger seat.

One thing I quickly found out from experience is don't buy a great antenna setup and then go cheap on the coax. Spend the money and get 50ft of LMR-400 as your main feed line and then run a couple of feet of LMR-240 or similar to the radio.