Looking for an RF connector adapter

Thread Starter

cmartinez

Joined Jan 17, 2007
7,764
I'm working on a project that requires the use of a GPRS modules for telemetry purposes. These modules have an SMT connector on their boards to which a small antenna is attached. See picture below.

My question is, is there an adapter out there that has the tiny RF connector used in the module on one end, and a standard 1/4 RF antenna connector on the other?

The point is being able to simply connect the GPRS module to a standard antenna using a 1/4 connector at its end. The type of connectors I'm referring to are shown below.

2c85c8d3-d516-4a92-b828-d90b38bab89d.jpg




1658581358541.png


1658581399604.png
 

AnalogKid

Joined Aug 1, 2013
10,113
A consequence of the miniaturization of cell phones over the decades is an increase in the number of very small RF connectors. If the cable connector in the photo snaps onto the board connector, it might be an SMB, and lotsa people make an SMA - to - SMB adapter or adapter cable. Try Pasternak and Bomar.

But based on the scale of the other components, it looks too small to be a standard SMB. To me this means that a rigid adapter probably is not available, and you will have to go with a short adapter cable.

Is what's on the board something like this:

https://www.pasternack.com/nsearch....rt=Sortsku:ASC&res_per_page=48&view_type=grid

ak
 
Last edited:

SamR

Joined Mar 19, 2019
4,336
Good luck. My experience has been that they were deformed/damaged in shipment and unconnectable. With the miniaturization, they are getting harder and harder to manually fit the connection. They were not designed to be connected and then disconnected. They are SMD unfortunately.
 

MisterBill2

Joined Jan 23, 2018
12,697
The problem using many of those connectors is a lot of them are intended for machine crimp only. So how to crimp one five cent connector without the $120 tool? Worse with the cheap junk connectors designed to be mated only once. Having an FT-990 trying to fix that has some of those connecting to a PCB that must be pulled out to check. CHEAP Crimp on connectors are the bane of servicing. (FT990 symptom is no transmit).
 

Ya’akov

Joined Jan 27, 2019
6,266
Hey, @cmartinez, keep in mind at the frequency you are working at transmission line loss is a serious concern. You lose a lot of power in those pigtails but that might not be avoidable. But if you intend to extend it further check the loss specification on your coax, it might surprise you.

Also, whatever antenna you intend to use, check it for resonance at the frequency of interest, Cheap SMA terminated antennas are a crap shoot. Some are mislabeled, some are simply no good, and a few are decent. For the little ones, they all use the same radome so visual inspection doesn’t help.

If this is for a learner project invest in a NanoVNA for ≤ ~100USD and learn to use the SWR portion (a couple hours’ investment) it will let you keep your hair instead pulling it out if the link is poor.
 

Ya’akov

Joined Jan 27, 2019
6,266
Hey, @cmartinez, keep in mind at the frequency you are working at transmission line loss is a serious concern. You lose a lot of power in those pigtails but that might not be avoidable. But if you intend to extend it further check the loss specification on your coax, it might surprise you.

Also, whatever antenna you intend to use, check it for resonance at the frequency of interest, Cheap SMA terminated antennas are a crap shoot. Some are mislabeled, some are simply no good, and a few are decent. For the little ones, they all use the same radome so visual inspection doesn’t help.

If this is for a learner project invest in a NanoVNA for ≤ ~100USD and learn to use the SWR portion (a couple hours’ investment) it will let you keep your hair instead pulling it out if the link is poor.
“Learner” should be “larger”.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,764
I know very, very little about RF tech and such. So any advice and observations are extremely welcome. As I said, this adapter is to be used on a GPRS module for an iOT application of sorts. And the working band is Cat-M, which works in a narrow 1.4 MHz band. If I understand its specs correctly.

What's a NanoVNA and what does it do?
 

Ya’akov

Joined Jan 27, 2019
6,266
I know very, very little about RF tech and such. So any advice and observations are extremely welcome. As I said, this adapter is to be used on a GPRS module for an iOT application of sorts. And the working band is Cat-M, which works in a narrow 1.4 MHz band. If I understand its specs correctly.

What's a NanoVNA and what does it do?
The links @bertus provided should help with the NanoVNA. As far as CAT-M is concerned, and you may already understand this, the 1.4MHz is the channel bandwidth, not the operating frequency which is the concern of the antenna. That could be anywhere from 700MHz—5+GHz depending on the allocations near you.

But I neglected to ask, “why not use the supplied antenna?”
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,764
and you may already understand this, the 1.4MHz is the channel bandwidth
Yes, that is what I understood from the specs. Thank you. I failed to clarify the operating frequency.

But I neglected to ask, “why not use the supplied antenna?”
That's because the device will be encapsulated in a metallic container, and will also be installed underground. Therefore the use of an external antenna becomes necessary. The adapters I bought are intended to be used from the device to the enclosure's lid, and then an antenna such as this one is connected to the lid.

1658672530145.png
 

Ya’akov

Joined Jan 27, 2019
6,266
Yes, that is what I understood from the specs. Thank you. I failed to clarify the operating frequency.


That's because the device will be encapsulated in a metallic container, and will also be installed underground. Therefore the use of an external antenna becomes necessary. The adapters I bought are intended to be used from the device to the enclosure's lid, and then an antenna such as this one is connected to the lid.

Well, in light of this I strongly suggest you get the NanoVNA and characterize the antenna's resonance. WIth a 3m cable, not counting other signal path losses and assuming it is RG174 (which it looks like) at 2.4GHz there will be about 7.7dB of loss.

That's a lot. Testing will be important. It is possible that you might want to use directional antennas (small Yagi-Udas) in some locations. If there is very good cell coverage in the areas involved this may moot. By the way, I don't trust that antenna.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,764
By the way, I don't trust that antenna.
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...
 

MisterBill2

Joined Jan 23, 2018
12,697
If that antenna covers such a wide frequency range then probably it needs to be tuned to the frequency you intend to use. And that 12 dbI "gain" is relative to a mythical isotropic radiator, not a realizable antenna. It actually looks a lot like the antennas that used to be installed for cell phones in cars, back in the era when cell phones were actually installed in cars.
 

bassbindevil

Joined Jan 23, 2014
499
Making an antenna more directional will increase the real gain, if your wireless link is in a fixed location. A simple reflector can be added to an existing antenna, or there are cantennas and Yagis you can make yourself.
 
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