Larsen TRI-Band VNA Sweep (Part Deux) + Laird Scanner and COMPACtenna SCAN III

[devicelab]

Okay I have more egg on my face. I forgot about my scanner NMO cabling in the SUV and grabbed the wrong coax. THIS time I have labelled my connectors so I know which is which!

Here are the real VNA sweeps between the older Larsen TRI-BAND and the new Larsen 150/450/758 (which coincidentally match their own measurements!)

 

[devicelab]

Here is the Laird Scanner antenna:

 

[devicelab]

Here is the SCAN III antenna:

 

[mmckenna]

Photos are not showing up. I'd love to see them.

 

[devicelab]

Photos are not showing up. I'd love to see them.

Working for me..? Check your interwebs! ;o)

 

[prcguy]

The Laird scanner antenna is resonating around 176Mhz on VHF, not ideal. I also see the COMPACtenna return loss is only about 9dB on VHF and those antennas are sensitive to the ground plane, they want less and preferably at the edge of a roof. Was the testing done with COMPACtenna in the center of the roof?

 

[devicelab]

The Laird scanner antenna is resonating around 176Mhz on VHF, not ideal. I also see the COMPACtenna return loss is only about 9dB on VHF and those antennas are sensitive to the ground plane, they want less and preferably at the edge of a roof. Was the testing done with COMPACtenna in the center of the roof?

Yep I noticed that too. And yes the scanner NMO is almost directly center.

 

[mmckenna]

Working for me..? Check your interwebs! ;o)

Hmm, must be the Bill Gates nanobots I had injected today. That and I feel suddenly compelled to buy Microsoft stock...

 

[prcguy]

If you have another mount that is compromised on the ground plane give the COMPACtenna another run through. Even with a COMPACtenna in the center of my roof it was outperforming a Larsen and Laird on VHF and most other bands with actual reception.

Yep I noticed that too. And yes the scanner NMO is almost directly center.

 

[prcguy]

Now you will spend much of the time in the bathroom rebooting.

Hmm, must be the Bill Gates nanobots I had injected today. That and I feel suddenly compelled to buy Microsoft stock...

 

[cbehr91]

More food for thought - my COMPACTenna (that is now prcguy's) worked better when there was no rubber gasket/o-ring thingy between the bottom of the antenna and the surface below. I think it affected the contact between the NMO mount and the metal tab on the antenna.

 

[devicelab]

More food for thought - my COMPACTenna (that is now prcguy's) worked better when there was no rubber gasket/o-ring thingy between the bottom of the antenna and the surface below. I think it affected the contact between the NMO mount and the metal tab on the antenna.

Hah funny you mentioned that. I had that installed for several months and today I noticed the copper tab was pressed almost completely down to the insulator. I pulled it back out a bit before I installed it. After I measured it -- it was almost back down again but not quite.

The SCAN III is a decent compromise antenna but still works fine on 700/800 Mhz -- but I'm enjoying the Larsen 758 now. It's built like a tank and reception is fantastic.

Has anyone tried a MP Antennas Super M Classic?

 

[vagrant]

Thank you for posting those sweeps. It made me plot the older Larsen and Scan III just now and my results are very similar to yours, except for 700 MHz and up. Mine was a bit worse there, but no surprise due to my coax type and length of it. I use an NMO lip mount on the side of the hood near the passenger pillar.

Besides a sweep, over time I have switched back and forth between the older Larsen and Scan III in a suburban area. What is interesting, keeping the sweeps in mind, is that I have a slightly improved signal quality on weak signals ( via my ear ) while using the Scan III. I have also tested the two with a significantly reduced ground plane and there the Scan III pulls ahead in the sweep. The Scan III is different, but is it worth twice the price of the Larsen? If the mounting location has a compromised ground plane, or a short antenna was needed, I would say yes.

Still, even mounted on the side of my hood with an NMO lip mount, the new Larsen 150/450/758 may provide improvement. Plus, it offers that fancy spring. I'm $50 and a week away from finding out.

 

[CanesFan95]

How do you read these sweep things? What's on the x & y axes and what are the different colored lines?

 

[prcguy]

If you look at everything on the display it should explain itself.

How do you read these sweep things? What's on the x & y axes and what are the different colored lines?

 

[devicelab]

Here's a rushed sweep from a Motorola All-Band antenna (the fat boy model) -- (from a different vehicle with center-rear NMO mount) --

 

[devicelab]

Here's a pic of that Motorola antenna:

 

[toolman60]

devicelab,
A bit of thread hijacking.
Is the little Nano VNA accurate enough for trimming antennas? I was looking at getting 1 for antenna trimming and building. There so many mixed reviews on them fake vs original I was curious how yours performed. I need to build a 1691 mhz feed for my daughters GOES dish.

 

[devicelab]

Is the little Nano VNA accurate enough for trimming antennas? I was looking at getting 1 for antenna trimming and building. There so many mixed reviews on them fake vs original I was curious how yours performed. I need to build a 1691 mhz feed for my daughters GOES dish.

Can't really comment about the 'little' version. I don't own that one -- never have. The original NanoVNA was pretty small and somewhat limited. Eventually a newer model was created with improvements (including a metal case) called the NanoVNA-F model.

The newest version is called the NanoVNA-F V2 and goes up to 3 Ghz (plus other minor tweaks.) This current model seems to be very accurate (with proper calibration) and the firmware/software seems very stable. Updates seem to be provided regularly. The model I have is more expensive than the cheaper, smaller model but it's proven itself over and over. It's a very powerful tool if you're willing to take the time to learn it. There are a ton of YouTube videos to help understand the theory behind it and several on how to use it. I'm still learning mine. I just found out how to save the sweep data and then import it into the PC application... so that will make the sweeps a little easier to read.

Here's the model I purchased: https://www.amazon.com/gp/product/B0825PZNJJ

 

[devicelab]

I need to build a 1691 mhz feed for my daughters GOES dish.

Haven't used mine that high as yet -- so can't really comment on the performance but if you have the unit calibrated properly, it should be fairly accurate. The calibration kit is included with the V2 kit.

That being said, the included 50 ohm load isn't high quality. I bought a Mini-Circuits SMA version and while it's 98% acceptable for most users, I wanted something better. I got lucky and found a like-new HP Open/Short 50ohm calibrator and a HP 908A 50 Ohm reference load. (I also own the RigXpert AA-1400 so I can use them for both calibrations.)

I've done testing with 33cm HAM and 1090 ADS-B antennas with no problem.