Helical Antenna Fitting Type

I am looking to build a new mount for the M2 Helical and for my P4Pro. What is the actual fitting that is the connection at the antenna. I see SMA but don’t know anything about them and if there are different varients.


Off the top of my head, I think it is SMA on the antenna. The only two types of SMA plugs that I know of are SMA and RP-SMA (reverse polarity). In the amazon picture it is SMA as the female (nut end) has the pin inside. A RP-SMA has the receiver for the pin on the nut end. Off the top of my head I thin

1 Like

This is the cable I used in my M2 base box.

I had it connected to a SMA bulkhead through the box. My helical could screw right on it or I have a SMA cable extension for it as well. Since I got my new globe in, I added this cable to my box

This way I can use a normal TNC globe cable from my box to my globe. I still left the SMA cable. If I want to use it, I unplug one from the M2 and plug in the other.

1 Like

My goal here is to be able to mount the helical antenna on top of the P4 Pro without needing the mast like you would see on the Tuffwing kit. Depending on the link of the fitting I’ll put an appropriate grommet with a pass through for the cable. I’m hoping it is about a 1/2" and should look pretty clean. I’ll have to look into those cables to see if I can get something shorter than what comes with the Emlid kit.

I just got a response back from another fitting manufacturer and the dimension is 15 mm so that should work well.

Not sure what a Tuffwing kit is. If you are mounting it through something, I highly recommend a bulkhead. This isn’t the “brand” I used but it is the same thing. It has enough thread on it to go through a normal plastic wall thickness with enough thread for your Helical antenna to mount on. You would just add a cable like I did to the bulkhead. If you search Amazon, you can find different lengths. I needed short ones for my base box.

I’ve got a couple of different designs in mind but I think the spacer method would be the cleanest and most stable. I’m not sure what you mean by bulkhead? Is that like a coupler?

Yes do a search on Amazon for a SMA bulkhead. It’s a coupler with an extra nut to mount it to another surface

1 Like

I’m just sort of guessing at what you are looking for. I have the Tallysman HC871 that comes with the Emlid M2. As you can see in the photo below, it uses two M2.5-0.45 machine screws to attach it to whatever platform you want, and it also has an integrated O-ring to seal it off. The cable also includes a nut for further attachment integrity. If that is the antenna you are referring to, I don’t believe you need anything fancy to mount it. Just drill the antenna hole to fit your cable thread, and two small holes for the M2. 5 screws.

1 Like

I will be putting it on top of a Phantom 4 Pro drone. Since the cable it comes with is straight it will not mount flush and bending it is probably not a good idea. I thought adding a 90 adapter would be the cleanest solution to get the antenna off the shell.

A few additional clarifications to my note above. If you look at the end of the stock antenna cable, you can see two nuts. The rear nut (furthest from the end) is used to tighten the cable end into the antenna. Then the closest nut can be used to pull the antenna assembly tight to whatever mounting surface it is on. But I wouldn’t put much force on that nut.

The M2.5 machine screws are intended to hold the antenna to the mounting surface. Again, not too much torque as they are very small screws.

Altogether the three attachments ought to provide plenty of pull to seal the o-ring to the mounting plate. I really don’t think a bulkhead of any kind is required. The antenna is very low mass and it is already weather tight.

1 Like

I see. So the issue isn’t getting it tight and sealed, it is getting the cable attached without any clearance inside the drone.

While I don’t use my drone with RTK or anything similar, I do have a Phantom 4 that I use for aerial photography. It’s a pretty beefy unit. It would easily lift 30 Emlid’s and their antennas. A small riser wouldn’t compromise it one bit. I’d consider mounting your antenna on a little riser just high enough (say two inches?) to allow the antenna cable to bend 90 degrees without overstressing it.

If I were doing it, I’d machine an aluminium or plastic (or even wood) post with the same taper as the antenna and drill holes for the screws as well as an access slot for the antenna cable. It would just make the antenna look a little taller than it is.

1 Like

I am very familiar with the kits so this is for trying to figure out what the connector actually is and not how to install. We’ve got the design drawn up, but thank you for the suggestions.


Ah, ok. I guess I totally misunderstood.

The HC871 has a male SMA connector built into it. However, you have to watch the Male/Female designations on the confusernet. Technically they should be based on the actual center conductor (which is male as you can see in the photo of the antenna) but they are sometimes designated based on the threaded part which is female in the same photo.

Just found this.

So it looks like I need an SMA Female to an SMA Male 90. Doesn’t sound like something I will find so there would probably be a coupler involved? I think the idea of making the spacer a little taller so I can gently bend the cable is probably a better idea. Now to find a 25cm (10in) cable. I can make something a little longer work.

1 Like

So your photo is a perfect example of how the confusernet works.

The two connections on the left are correctly labelled as male and female. The two on the right are incorrectly labeled. Their polarity should be reversed. This is a very common error and you just have to be careful to get the one you need, which might not be what they are called. In the industry, it is the pin that carries the signal that determines the sex of the connector. So it either has a male pin or a female socket that the pin fits into.

Moral of the story. Be careful.


This looks right for the original design right?


Yes, I believe so. Hopefully, it is also labelled as SMA. (the size is not obvious)

In your photo, male is on the left and female is on the right. The female end goes to the antenna and the male end goes to your cable.

It’s the same as my original post - you just can’t quite tell if there is a pin on the external threaded side. I guess that would be normal male to RP male then wouldn’t it?

Don’t know what normal means… Lol!

1 Like