Good 2m SWR on UHF Antenna?

[BadM0nkey]

Hi, my first post here. Passed my Technician's Exam a week ago and waiting for my call sign....

A few months back (before it occurred to me to get my Amateur License) I paid for my GMRS license and put up a Tram 1486 UHF Land Mobile Base Antenna up on 20' of 1.25" conduit. I cut-tuned it to a VSWR of 1.1 on the high-power part of the band at 467 MHz with a VSWR of 1.4 at 462 MHz.

The meter is a Surecom SW-102 Digital VHF UHF 125-525Mhz Power & SWR Meter.

My friend came by today with his dual band mobile and we found that the VSWR is 1.99 at 449.750 MHz and 2.29 at 445.925 MHz which seems to make good sense and is not great but workable.

What came is a big surprise was that on 2m at 144.310 MHz the VSWR reads 1.4 and at 147.580 1.12! How can this be? Will it be safe to transmit on 2m using this UHF antenna?

Thanks in advance.

 

[jwt873]

My friend came by today with his dual band mobile and we found that the VSWR is 1.99 at 449.750 MHz and 2.29 at 445.925 MHz which seems to make good sense and is not great but workable.

What came is a big surprise was that on 2m at 144.310 MHz the VSWR reads 1.4 and at 147.580 1.12! How can this be? Will it be safe to transmit on 2m using this UHF antenna?

Congrats on getting your ticket..

I might be reading your question wrong, but an amateur dual band antenna should have a low SWR on both 440 and 144 Mhz. They're designed to operate on VHF and UHF hence the word Dual....

 

[popnokick]

True about dual band VHF-UHF antennas.... but in this case, the specified Tram 1486 is NOT shown as a dual-band antenna, but a UHF base antenna. However, look at the pdf on the Tram website and you'll see that in the Tram 148x series there are VHF, UHF, and dual-band fiberglass base antennas, each having a model number of 148x with only the last digit distinguishing the difference. So to the OP: Are you sure what you have is a 1486? The entire series of antennas is virtually identical. Could the wrong unit have been packaged, shipped, or ordered... and ended up with you somehow? Did you get it from someone who said it was a 1486? Seems like the UHF SWR should be lower (per the spec sheet)... so am wondering if it is really a VHF or dual-band base antenna in that series.... rather than the 1486.

 

[BadM0nkey]

Congrats on getting your ticket..

I might be reading your question wrong, but an amateur dual band antenna should have a low SWR on both 440 and 144 Mhz. They're designed to operate on VHF and UHF hence the word Dual....

The antenna was advertised only for UHF and the cutting chart was only for UHF frequencies...

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[BadM0nkey]

Great question. I was wondering the same thing but it is definately the 1486. It has very short radials and has a single section fiberglass shell.

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[prcguy]

If it has a good VSWR then it won't hurt a 2m radio transmitting into it but that doesn't mean it will radiate very well on 2m. If it actually worked as a dual band antenna the company would have advertised it that way.

Congratulations on passing your amateur exam and its a great way to learn about antennas. You'll find VSWR is just one of many antenna parameters and some antennas like for HF, VSWR has no bearing on now well the antenna radiates and on other types with a great SWR will not get across the street.
prcguy

 

[BadM0nkey]

Thanks. I will start reading the General material in a couple of weeks.

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[cmdrwill]

If it has a good VSWR then it won't hurt a 2m radio transmitting into it but that doesn't mean it will radiate very well on 2m. If it actually worked as a dual band antenna the company would have advertised it that way.

Congratulations on passing your amateur exam and its a great way to learn about antennas. You'll find VSWR is just one of many antenna parameters and some antennas like for HF, VSWR has no bearing on now well the antenna radiates and on other types with a great SWR will not get across the street.
prcguy

Correct about the VSWR Vs the actual radiation of the antenna. One way to tell is to change the length of coax cable between the antenna and VSWR meter/transmitter and take another reading. A 'magic' length of coax cable with a short at the far end will have a very good low VSWR at some frequency. And none of this was on the Ham test, one has to learn by doing.

A short true story: Had a test setup for measuring antennas on an antenna range, and every time I added this one cable into the test setup, I got a gain in signal strength. The cable probably had a VSWR problem due to incorrect coax connector installation or something. That cable went flying into the arroyo, and is probably still there to this day.

 

[SpugEddy]

This may sound stupid, but make sure the SWR meter you are
using is compatible on both VHF and UHF. I've used a UHF meter
on VHF and got great readings. When i hooked up the right meter
the readings were entirely different

 

[BadM0nkey]

This may sound stupid, but make sure the SWR meter you are
using is compatible on both VHF and UHF. I've used a UHF meter
on VHF and got great readings. When i hooked up the right meter
the readings were entirely different

Thanks. It is definately a VHF/UHF meter. I am also sure the Coax and connections are sound. I can reach a repeater 65 miles away on GMRS frequencies with a 5W handheld.

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[SCPD]

Hi BadMonkey-
.
I am not familiar with that Tram antenna, but here’s a few general things you might keep in mind about V/UHF antennas - stuff in general.
.
Many ‘Gain’ antennas will resonate at several surprisingly diverse frequencies. For instance, your Tram may well be design'd as something on the order of a ¾ wave antenna at UHF, but also it is (unofficial) like a ¼ on VHF ( 450/150 Mhz)-- the broad band-ness of the design may make it workable over a wide variety of frequencies- as your SWR readings confirm. Since you have a good meter, I’d accept those readings as valid.
.
It is, however, one thing to get a nice resonate antenna- and for 90% of the time that’s fine--- the down side is that you aren’t sure about the radiation pattern when using it off-band. It could be quite acceptable-- for working satellites !- or maybe the moles down in your lawn-- you just don’t know where the RF is going. However, its radiating, the transmitter likes it, and if it ‘hit’s the repeaters’ and simplex stations talk to you---who cares if the pattern looks like Bullwinkle the Moose in profile.
.
Personally I like very (!) simple antennas… especially mobiles. Long ago I got into the standard 18 inch Motorola NMO mount'd verticals for dual band radios- a single antenna will work for both 2 an 440--
Yes, yes, and I know guys, not a perfect SWR -- but less than 2:1 which is fine with me. These are simple, unobtrusive and work well as far as I’m concern’d.
.
I’ll tell you a brief story- ongoing to this very moment. We have a remote site that is being wired for telemetry on a UHF frequency. The system is supposed to work on 409.4Mhz (a totally made up number for illustration) --but its antenna will NOT resonate on that frequency!!-- This is an very expensive commercial XYZ antenna too.. Try as we can with all sorts of tricks, ‘phone calls, etc.,-- Nada. It’s SWR will dip beautifully at 409.3 and 409.5-- but flies off the charts at 409.4.……….Groan.
..
After 2 days of this and I am about to yell;
.
“….Either pick an new channel, or junk that thing and use a quarter wave whip.. “
.
…………………….So much for the engineer in me.
.
I say all that to tell you BadMonkey, that if works- smile, and don’t question it too much.
.
…………………….CF

 

[BadM0nkey]

Thanks for the wisdom CF. I am not all that concerned about a nice circular radiation pattern and would prefer if it went straight up for satellite communications [emoji4] . Been preparing to build a couple Eggbeater IIs to hunt the ISS.

I have good east and south coverage from here and can hit a repeater in New York something like 65 miles away on 467MHz. West and north of me about 2 miles is a 1450' ridge made mostly of quartz which is a serious obstacle.

Who wants to speak to Canadians anyway [emoji6]

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[SCPD]

I like your Moxie, BadMonkey ...
.
You'll do just fine in this hobby
.. and Welcome aboard !....
.
........................CF

 

[bill4long]

The antenna plus the particular length of coax may be rendering a decent impedance, close to 50 ohms. But as the other poster said, this does not mean that the antenna is a good radiator for 2m. A dummy load has a perfect SWR and they are lousy radiators (on purpose.) Go ahead and see what kind of performance you get on 2m with this antenna. You won't hurt the radio. But I wouldn't run it on high power.