Laird Phantom UHF (430-450)

[devicelab]

So here's my sweep of a Laird Phantom UHF (TRAB4303) on a high quality mag mount (RG8x) with a large ground plane:

It's very good and obviously very usable for HAM work. I'm a bit puzzled why it's centered at 430 Mhz and not 440 Mhz.

Has anyone measured the TRAB4503 model? I'm curious if it's centered at 450 Mhz -- in which case it probably would be slightly better for HAM work.

PS. I will try this on my roof mounted NMO in the near future. It might be slightly better than the above but I kind of doubt it'll make that much difference.

 

[mmckenna]

There is LMR stuff down there in the 421-430 range in select parts of the country. And other countries have different allocations.

Probably not designed for ham use, but it appears to work well enough. Usually the part number is where it's centered at.

 

[devicelab]

Usually the part number is where it's centered at.

Well the funny thing is the product literature (and web site) says 430-450 Mhz... so I presumed it was centered at 440 Mhz. Also this is not tunable so whatever... The whip numbering scheme I can understand but they're 'longer' and can be tuned to a specific frequency. Not a big deal but confusing to say the least.

I noticed the TRAB4503 model is almost double the price of this model. Ah well.

 

[mmckenna]

Yeah, one of the reasons why I don't use them. Haven't run into anything they really solve for me.

Try it on a permanent mount and see if it changes. I've seen variations between magmounts and permanent mounts.

 

[CanesFan95]

So looking at the left edge of the graph, it says "3.84V". Is that 3.84 volts and what voltage is that? And the numbers on the left side go 0.0, -5.0, -10.0, -15.0, etc. from top-to-bottom. What do those numbers mean?

 

[devicelab]

So looking at the left edge of the graph, it says "3.84V". Is that 3.84 volts and what voltage is that?

The analyzer has a built-in battery and that's displaying its current battery level. It has no bearing on the measurement.

 

[mmckenna]

And the numbers on the left side go 0.0, -5.0, -10.0, -15.0, etc. from top-to-bottom. What do those numbers mean?

I believe the yellow numbers on the left side of the screen are return loss in Decibels.
The blue numbers on the right are Standing Wave Ratio (SWR).

 

[CanesFan95]

So return loss, is it better to have less of that I'm assuming? I don't understand the phrase "return loss" because I'm assuming you don't want any of your transmuted signal to return back to the radio. So you want less return but you also want less loss. If there's more loss in the amount of signal being returned (say, because of coax loss), wouldn't tmore return loss mean there's less returned signal, which is better?

 

[mmckenna]

You want lots of return loss. That means that the signal is getting radiated/absorbed and not reflected back.

Some of that loss might happen in the cable.

But you want less loss in the cable, because you want the power to get through the cable as efficiently as possible.

 

[CanesFan95]

The numbers on the left side are negative and get lower. So if you want more return loss, would that mean you want a less negative number that's higher up on the graph?

 

[CanesFan95]

And the bottom axis says "START 350.000 MHZ", and "STOP 500.000 MHZ". What does that mean and what was it that was started and stopped?

There's something else on there that says "OSLT C# 2019". Anyone know what that is?

 

[mmckenna]

The numbers on the left side are negative and get lower. So if you want more return loss, would that mean you want a less negative number that's higher up on the graph?

You are right, maybe I'm misreading it. More return loss is better.

Antenna Return Loss and VSWR Explained Without Math

Find out what return loss and VSWR in antennas is all about. How does it affect performance and how to measure it.

antennatestlab.com

 

[mmckenna]

And the bottom axis says "START 350.000 MHZ", and "STOP 500.000 MHZ". What does that mean and what was it that was started and stopped?

It's what's called a tracking generator.

It's an RF signal generator that sends out a low level signal to the antenna and the spectrum analyzer looks at what gets returned.
You usually set the signal generator to sweep the usable spectrum of the antenna. In this case, the signal is sweeping from 350MHz up to 500MHz and just keeps doing that. The Spectrum analyzer looks at the returned signal on the same frequency that the tracking generator is currently on.

There's something else on there that says "OSLT C# 2019". Anyone know what that is?

I don't know. Just checked mine and I don't see that.

 

[CanesFan95]

It's hard to tell from the display what exact frequency had the lowest SWR where the blue line is lowest, and what range of frequencies were under 1.5 SWR.

The top of the display says "611 LOGMAG 5 dB" and "-16.22dB S11 SWR .5/ 1.37" and another line "<1++ 446.000 MHz-16.22 dB 1.37", not sure what all that means. And I though decibels (dB) was a measurement of volume, like how loud an airplane is.

 

[mmckenna]

446.000MHz is where the #1 marker is. It's showing a 16.22dB return loss, which equals about 1.37:1 SWR.

Decibels are a logarithmic measurement when comparing electrical signals. That could be sound, or RF.

 

[devicelab]

There's something else on there that says "OSLT C# 2019". Anyone know what that is?

Calibration data that's all. The last part is actually "201P" for 201 Points... as in data points.

 

[devicelab]

The numbers on the left side are negative and get lower. So if you want more return loss, would that mean you want a less negative number that's higher up on the graph?

No, a higher negative number means a low "return" loss. The two graphs are essentially the same. The data is just being displayed in different formats. That's why the images look like a mirror image. The low SWR point is the maximum return loss at that frequency -- that's because they're measuring the same thing. Different terminology for different specific values.

 

[CanesFan95]

Wouldn't that be the minimum return loss since the part with the lowest (best) SWR has the yellow line at the most negative number? (-25.0 is less return loss than say, -5.0?)

 

[devicelab]

Try it on a permanent mount and see if it changes. I've seen variations between magmounts and permanent mounts.

Well now. This is more like it!

I'm really surprised by the difference between the magnet and roof mount. I understand the technical reasons why magnet mounts suck but I thought UHF wouldn't be quite as affected -- but I was way off on that.

Here's the NMO roof mount with the Laird Phantom:

 

[devicelab]

Just to be clear, the first pic was using a Laird magnet mount with RG8x and an N connector. It sure seems like the magnet mount cannot use the ground plane as effectively.