Whistler Scanner Antennas

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Machria

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Not doubting your sweeping skills or the antenna performance, but that looks a little suspect to me.

You should ABSOLUTELY doubt my "sweeping skills"!! I really have no idea what I'm doing with the vna. But I'm reading a lot, following the detailed instructions on the io groups site, lots of great info on there. It's easy for me to figure out and operate the software on the device and on the PC applications with my software background. But understanding what it is showing me electronically is a whole other story. I'm just trying to learn enough to allow me to help set my new "ham shack", and tune a couple antenna's.... ;-)

That previous shot probably looks "suspect" because it is such a wide sweep, I'm guessing it's missing all the real detail in between.... but total guess on my part. Maybe somebody who know's what they are doing will chime in and fix all the mistakes I'm 100% sure I'm making! ;-)

Here's what the 800MHz band looks like...
Whistler 758MHz-830MHz.jpg
 

jonwienke

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Not doubting your sweeping skills or the antenna performance, but that looks a little suspect to me.
The huge VSWR spike around 35MHz is squashing the rest of the chart down into unreadability. @Machria rerun the test with the vertical axis limited to 5 or so, so the huge spike gets clipped and you can get something meaningful from the rest of the plot.
 

KevinC

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The huge VSWR spike around 35MHz is squashing the rest of the chart down into unreadability. @Machria rerun the test with the vertical axis limited to 5 or so, so the huge spike gets clipped and you can get something meaningful from the rest of the plot.

I zoomed in and see a limit line at 2.0 (I believe). So yeah, turn off auto-scale if it's on.
 

Machria

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Any coaxes you use has to be calibrated out of the measurement. Put the calibration devices at the end of the coax.

/Ubbe

thanks... I do that with the shot jumper cables I leave on the nano to save the direct n connectors on it. BUT, there is a hardwired length (10’ or so) of coax attached to the antenna I need to calibrate out, that I have not read about how to calibrate out using the time delay... yet. I asked that question a while back on iogroups since most of my antenna testing will be on marine antenna’s which ALL have hardwired coax. They directed me to a link explaining how, I saved that link haven’t had time to read and try it yet.

I was just playing with the nanovna yesterday to make sure it was working ok, not really doing any real “testing or analysis“ with it. I received a new nanovna and just wanted to make sure it was good out of the box. I had received another one previously that had some issues, turned out it was a bad knock off version. I’m going to sell that one for parts, and sell this new one, and order the new 4” H2 version. These things are just too small, even with the large font firmware on it.
 

PriorMike

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I bought a WMM 460 to try; I usually have an RS centre loaded telescopic whip on the back of my 996P2.

Inferior on both 800 and VHF by a fair bit, lost signal strength on the trunking sites I monitor. The only time it was an improvement was when I accidentally stuck it directly on top of the scanner, but I'm not sure of the long term effects of the magnet on the insides.

Disappointed.
 

iMONITOR

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I bought a WMM 460 to try; I usually have an RS centre loaded telescopic whip on the back of my 996P2.

Inferior on both 800 and VHF by a fair bit, lost signal strength on the trunking sites I monitor. The only time it was an improvement was when I accidentally stuck it directly on top of the scanner, but I'm not sure of the long term effects of the magnet on the insides.

Disappointed.

I'm not surprised.

Whistler would probably tell you the magnet helps pull signals out of the air! :rolleyes:
 

KevinC

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I bought a WMM 460 to try; I usually have an RS centre loaded telescopic whip on the back of my 996P2.

Inferior on both 800 and VHF by a fair bit, lost signal strength on the trunking sites I monitor. The only time it was an improvement was when I accidentally stuck it directly on top of the scanner, but I'm not sure of the long term effects of the magnet on the insides.

Disappointed.

Maybe it worked better on top of your scanner because it had a metal ground plane under it then. Just a thought...
 

Machria

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The huge VSWR spike around 35MHz is squashing the rest of the chart down into unreadability. @Machria rerun the test with the vertical axis limited to 5 or so, so the huge spike gets clipped and you can get something meaningful from the rest of the plot.

Just tried that for giggles, there is no way in the software (that I see anyway!) to adjust the scale of the graphs/plots. I'm using NanoSaver..
 

Machria

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Maybe it worked better on top of your scanner because it had a metal ground plane under it then. Just a thought...

I use one sitting on my desk (which is metal with a rubberized top on it), and the other is used on a bar top, 100% stone (quartz) and wood, no metal to be found anywhere near it. They both perform really nicely, blow away the 7 or 8 other antenna's I have (they all all small wip antenna's).
 

Mike_G_D

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In regards to the vna - I have no experience with the NanoVNA itself but have lots of experience with HP/Agilant lab VNA's so, in general:

1) Pick the smallest swath of spectrum possible - don't try to measure from DC to daylight in one fell swoop; in your case, though more work, best to measure at just the basic LMR bands of interest plus the civil and mil air bands if need be with SEPARATE individual runs - one of for 30 to 50 MHz, another for 138 to 174 MHz, etc.;

2) ALWAYS calibrate to a lab standard (or as close to as possible) open, short, through (assuming a 2 port device, if only single port, as in your case, you can omit the through standard), and load relative to the measure point from the VNA; so, if using cables between the VNA and the DUT (Device Under Test) make sure to calibrate out to the end of those cables before each new frequency range run;

3) As was mentioned try to use a resolution that works best for the kind of results you are graphing BUT if some results are really causing the graph to "squash" the bulk of the data (say an area of really bad SWR) you may have to break the test frequency range up into smaller segments to get readable and usable results.

Also, when dealing with unavoidable lengths of cable attached to the DUT and you have no equivalent DUT standards to use (as in your case) there is a rough workaround that isn't super accurate but may yield close enough ok results if used properly -

Port extensions - basically, if your VNA has this it kind of allows the ability to input a compensation that essentially "extends" the test leads out to the DUT. It CAN be pretty accurate IF all of the details of the coaxial test leads used are known, not just the length and the characteristic impedance but also the loss at the range of interest, velocity factor, etc. The more details the better of course also depending on what your VNA can accept as input compensation factors. This is where the "fudgy" approximation usually comes in. If you just want something close enough for a rough check what you can do is just "extend" the standard test cables already in place as at least the chracteristic impedance should be pretty much the same (50 to 52 ohms, typically). So, for example, if your antenna has a 16 foot coax lead then you can try "extending" the already compensated for test leads (assuming you have been using those and they were provided with the VNA) out to 16 feet with all other characteristics being the same. Not perfect but in the ballpark usually.

Though you could attach the DUT cables to the test cables and extend out to the full length of the combined cable lengths it should be better to attach the DUT cables directly to the VNA and just use the DUT. But this could depend on the mechanical stresses of the connectors and adapters used and you will have to make that call.

Speaking of adapters - try not to use them as much as possible, of course, as they will affect the measurements though, if in good condition and decent quality shouldn't by much especially when already doing a "rough and ready" approximation as the not fully compensated Port Extensions are anyway. But still - try to keep their use down and instead use only the minimum number of adapters possible. Better to actually get test cables that have the desired DUT connector at one end and the correct VNA connector at the other. Then you will have to have appropriate calibration standards that terminate in the same connection as the DUT so as to calibrate correctly. An alternative slightly less accurate variation is to have a set of the exact same leads terminated in the same connectors your standards use but otherwise exactly the same (length plus characteristics) as the cables you will use for connecting to the DUT. Second best option is to use only 1 adapter conversion so that you only do one connector type conversion - you really don't want to have to add multiple adapters for BOTH mechanical AND electrical reasons!

For the kind of test you are trying to do with a mobile antenna with fixed leads try and put the antenna on a flat ground plane with a cross section at least to a length needed for the lowest frequency you intend to test at (at the bottom of the civil air band it's about 25 to 30 inches; low band would be much bigger and you may have to omit that test or accept the otherwise present measurement compromise if including that band in your tests and using a groundplane size that is smaller than needed) and keep the antenna away from any metallic material as possible - say on a wooden table in the middle of the yard but with a metal sheet under the antenna for the ground plane unless the table is metal itself and can function AS the ground plane. Another option might be a car roof with the car located out in the open away from any metal (aside from the car body) objects.

Something I might do if given the same conditions is to note what the type of coax is that is attached to the antenna-DUT. Usually that is basic RG-58A/U or some equivalent for basic hobbiest mobile antennas. Then I would get an equivalent length of the same type, or as close as possible, and then connect the calibration standards to the end of that coax with the VNA at the other end and then run the calibration, open, short, and load for the test frequency range. Don't coil up the calibration test cable OR the cable to the antenna-DUT but try and run them both out as straight as possible away from the VNA. While at 50 feet this isn't really practical for most of us it should be doable if you have access to some reasonable open space at only 16 feet. Then you can avoid the Port Extension work-around.

-Mike
 
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Mike_G_D

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I bought a WMM 460 to try; I usually have an RS centre loaded telescopic whip on the back of my 996P2.

Inferior on both 800 and VHF by a fair bit, lost signal strength on the trunking sites I monitor. The only time it was an improvement was when I accidentally stuck it directly on top of the scanner, but I'm not sure of the long term effects of the magnet on the insides.

Disappointed.

Not really a good comparison. As others mentioned you should use a decent ground plane underneath the antenna. Try a metal pie pan or a metal filing cabinet, etc. Top of scanner is okay for UHF and above but not too great for lower frequencies. And if inside it will be very location dependent and easily affected by any nearby metal.
 

Machria

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Mike, thanks for the detailed info! I've done extensive research on all this, as I'm in the middle of building a brand new HAM shack for myself as well as getting my lic. after thinking about it for, oh, 40 years or so! ;-) I'm all over it.... fun stuff!

The NanvoVNA has some TDR functionality built in to approximate out the length of feed line attached.... I've already order a bunch of PL259 connectors / adapters and will be making a new set of calibration standards for the nanovna on 259's. I plan on using it mostly on Marine installations, which are antenna's with permanent feed lines attached 90% of the time. And of course on my own scanner and newly aquired ham (HF and VHF) antenna's.
 

PriorMike

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Not really a good comparison. As others mentioned you should use a decent ground plane underneath the antenna. Try a metal pie pan or a metal filing cabinet, etc. Top of scanner is okay for UHF and above but not too great for lower frequencies. And if inside it will be very location dependent and easily affected by any nearby metal.

As per my posts, I don't have room to rig a ground plane, and I don't want to leave the magnet on top as I'm concerned about it affecting my scanner long term.
 

Machria

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Interesting, I did a bit of non-scientific testing, and the whistler antenna does do better on the VHF bands if it has some metal under it. It doesn't seem noticeable on other bands as far as I can tell (just listening to scanner), but on VHF bands it is a noticeable difference. On my metal desk, it does fantastic and if I remove it and place it 8' away from the desk, I can tell the difference. And upstairs in my house I normally place it on a stone (quartz) bar, and it works fine. Next to the bar I have a big metal popcorn machine, like you would see a vendor have at a carnival. I placed the antenna on top of that, and it also has a slightly better signal on VHF. So it would seem it does like a ground plane of sorts.

I love this antenna, it really does blow away all the wips. I have compared it to several, a Diamond 800MHz, a loaded telescopic set at different lengths, the whistler standard antenna, a few no name brands from Amazon/Ebay, an old radio shack scanner whip, a couple bearcats... It does very well against all of them.

Don't forget, it does have adjustments on each of the 4 antenna's on it, just loosen allen screws on the base and you can adjust the lengths. I have not doen that yet, once I get a better handle on the Nanovna, I will set them to what I like best using it. Enjoy!
 
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