And I don't trust it either, Mr Mulder ... but that's what I have at this moment ... Anyway, it seems that NanoVNA is an invaluable tool and is a must if I want do things the right way. I'll be buying one immediately. Although I have no idea as to how to use it yet ... baby steps...

It's as complicated as full sized VNA but your initial use is very focused, and there are a lot of sources for help including YouTube videos.

 

Ok ... now that the subject has leaned to the antenna itself, I'm open to suggestions of better alternatives.

If you are operating in a single band, a single band antenna is far preferable. Ideally you will have at least a couple of options. One for good signal areas and one for weak,

For the good signal areas, a ¼λ vertical antenna with a decent ground plane is probably best. For the weak signal areas a "gain" antenna will be needed. Of course being passive devices, antennas can't amplify. The gain comes from a narrow radiation pattern—same power, less area.

In this case a simple 3-5 element Yagi-Uda array is probably a cheap and effective option. But you have to do field work and figure out the signal strength you've got and if there are any obstacles. At the frequencies you are using it is mostly direct line of site that is required. This may mean elevating the antenna.

If you do put then antenna on a mast, please consider putting the radio portion up there too. Run power, data, and controls signals up the mast, not RF. Of course this all depends on how good coverage is in the location.

Keep in mind that in an urban setting you might be getting a signal reflected off a building that you can't otherwise receive. Figure out which cells you are in and see if you have line of sight. If you don't but still have a marginal signal, you may need to point the directional antenna at the building (or other reflector) rather than at the cell, possible even pointing it in the opposite direction.

If you are mounting antennas outdoors use dielectric grease and coax seal. if you don't, you will be servicing the antenna in just a couple of years. Also, make sure the coax you use is designed for UV exposure (sun) or it will breakdown eventually.

There's a lot of other stuff but I will try to bring it up as you are working on this.

 

As Bill said...

looks a lot like the antennas that used to be installed for cell phones in cars

Which means it uses the car body as a ground plane in its design. The NanoVNA is very popular among Hams for antenna and cable work. In fact, I bought one but have yet to spend the time learning to use it. One of many things on my to-do list. That type of mag-base antenna usually needs to be fine-tuned. For some it is a simple screw lock on the base to adjust the wire length of the active antenna. At high freqs that can be very touchy due to the short wave lengths.

 

Hello,

If you want to know more about RF design, perhaps this book might give you some insight:
https://archive.org/details/exp-meth-in-rf-des/mode/2up

Bertus

 

As the device, whatever it is, "will be sealed in a metal container and buried underground", I am wondering if the application would allow some portion of that assembly to include a molded or machined support for a single vertical antenna element.
Of course we have no clue as to what the device is or it's application. Back in Vietnam there were used by the US military, some small packages intended to provide information about humans passing by. (note the lack of details) Those devices used some radio frequency to transmit data for some distance.
That sort of application would justify a bit more effort than a device intended to monitor flower bed irrigation conditions..
Some sort of plastic cover that could be some part of the assembly while supporting the antenna might be a worthy consideration.
If this is for some college research project, then the plastic portion would more likely be machined, rather than molded. And the plastic portion could support the associated electronics, allowing for a very short transmission line, giving lower losses.

 

As the device, whatever it is, "will be sealed in a metal container and buried underground", I am wondering if the application would allow some portion of that assembly to include a molded or machined support for a single vertical antenna element.
Of course we have no clue as to what the device is or it's application. Back in Vietnam there were used by the US military, some small packages intended to provide information about humans passing by. (note the lack of details) Those devices used some radio frequency to transmit data for some distance.
That sort of application would justify a bit more effort than a device intended to monitor flower bed irrigation conditions..
Some sort of plastic cover that could be some part of the assembly while supporting the antenna might be a worthy consideration.
If this is for some college research project, then the plastic portion would more likely be machined, rather than molded. And the plastic portion could support the associated electronics, allowing for a very short transmission line, giving lower losses.

The device won't be buried underground, but rather installed underground. To be specific, they are to be used for telemetry purposes in drainage systems. The normal practice is to use an antenna with a magnetic base attached to the underside of the metallic lid of a manhole in the ground. Of course, the lid itself acts as an RF shield of sorts, but quite a bit of the signal can go through the sidewalk/pavement.

If you are mounting antennas outdoors use dielectric grease and coax seal.

Mind elaborating? Are those used for the junction between the cable and its connector?

 

Mind elaborating? Are those used for the junction between the cable and its connector?

The dielectric grease is used on the threads of the connector (don’t get it on the center pin or in the socket on the female connector. It will protect the connector of ingress of moisture and siezing.

The Coax-Seal is a kind of type a little like a mastic. It is self-fusing and adheres to the connector body and coax jacket but can be removed relatively easily.

 

The dielectric grease is used on the threads of the connector (don’t get it on the center pin or in the socket on the female connector. It will protect the connector of ingress of moisture and siezing.

The Coax-Seal is a kind of type a little like a mastic. It is self-fusing and adheres to the connector body and coax jacket but can be removed relatively easily.

Now that you mention it, I found this product and it looks rather promising. But I'll definitely be applying your Coax-Seal suggestion in my project.

 

OK, now we know a lot more. Under a manhole lid is certainly not a benign location. If the device is some distance away then the lowest loss transmission line is important.