antenna primer

[watermelonman]

I have a few GPS units that have simple wire stick antennas.

They work well enough, but I have been thinking about upgrading the signal as well as hopefully adding some flexibility. I think I have seen various combinations of RP and SMC in abbreviation form.

I am not sure how having a real antenna connector differs from having a stick antenna? My best guess is that by convention manufacturers have a few solder pads, one of which can be used as antenna directly, but if the others are connected it behaves in a different manner? Put another way, I am not clear on why putting a connector in the same place a stick antenna goes does not simply cause the entire connector and attachment to behave as a stick antenna.

Any explanation or guidance on good connectors would be appreciated. Thanks!

 

[ksaves2]

Question: What devices do you have? If you are referring to RP-SMA connectors they are something like this: https://www.ebay.com/sch/i.html?_fr...ctor.TRS0&_nkw=RP-SMA+edge+connector&_sacat=0

I use a plain SMA connector that has a "female" center pin just simply because I had that hardware lying around. Antennas can be had for either mode. One can strive to get an antenna tuned to the center of the band they are in.
That results in the most efficient transfer of Rf from the transmitter to the "ether" or air. For instance, if one can get an antenna that is tuned for 915Mhz that is going to be the most efficient antenna for transmitting and receiving.
Using a couple of Mhz on either side still shows decent performance.

On can do a bulkhead mount with an interconnect: https://www.ebay.com/itm/cable-RP-S...928533?hash=item360a882515:g:waoAAOSw~otWg8Hl
You plug this to the jack on your transmitter and stick the antenna say on the aft bulkhead so it's out in the breeze at apogee. This avoids having the antenna inside the ebay paralleling the all-thread.
One can also add a short interconnect cable, connect the antenna to that and rubberband it to the harness. Of course a nosecone mounted tracker can avoid this as long as all-thread isn't used to secure the bulkhead to the N/C shoulder.
A thick centering ring with blind nuts epoxied in the shoulder and perhaps with screws is sufficient. No doubt, more folks with answer. Kurt

 

[Worsaer]

I agree with Kurt, the proper frequency antenna in a bulkhead mount (outside the AV Bay), can perform well if you have space to do it. And to clarify, there are SMA connectors and Reverse Polarity (RP-SMA). I have found some eBay sellers don't always properly identify them, or worse yet, post the same photos for both.

This is a photo of my L3 project's 5" AV bay that uses an external antenna for a Real Flight Systems GPS-1.

 

[OverTheTop]

Here is what I have done in my Apache:

Details here if you want:
https://www.ausrocketry.com/forum/viewtopic.php?f=6&t=5019&hilit=apache&start=16

What is not visible in the picture is that the wire antenna is supported above the G10 fiberglass sled. Those are M5 nylon bolts, and the wire is fed through holes near the end of the screws, so the antenna sits about 15mm off the sled. That makes it more of an air dielectric and hopefully keeping it closer to the required electrical length. Proximity to the sled would slow down the EM waves due to the higher (~4.2) dielectric constant, making the antenna a little physically too short I think. Probably not a huge effect, but not difficult to do, so I did it. The screws are just threaded into tapped holes in the fiberglass.

You also can't see that the wire clears the metal parts at the tip by about 20mm.

 

[BDB]

This is a photo of my L3 project's 5" AV bay that uses an external antenna for a Real Flight Systems GPS-1.

What's the curly thing in the AV bay? And did you build that AV Bay without all-threads, or are they just hidden from this angle? (I've been wanting to figure out a way to do that, so I could keep my Eggfinder antennae in the the bay without sacrificing performance.

And if I can expand on the OP's question, could someone explain half wave vs. quarter wave antennas? I think I understand, but I would really appreciate some clarification.

 

[mikec]

I have a few GPS units that have simple wire stick antennas. They work well enough, but I have been thinking about upgrading the signal as well as hopefully adding some flexibility.

It's not obvious that having different antennas with connectors is going to improve the signal much, if at all. You might be able to boost the antenna gain by a dB or so but that won't really matter much. The main reason to use connectors is if you need to have the antenna somewhere away from the radio proper.

 

[Worsaer]

It's not obvious that having different antennas with connectors is going to improve the signal much, if at all. You might be able to boost the antenna gain by a dB or so but that won't really matter much. The main reason to use connectors is if you need to have the antenna somewhere away from the radio proper.

To reinforce Mike's point, adding cables and/or connectors results in signal loss. The reason to do it would be a trade off, locating the antenna in a more desirable location (like outside a carbon fiber airframe).

 

[Worsaer]

What's the curly thing in the AV bay? And did you build that AV Bay without all-threads, or are they just hidden from this angle? (I've been wanting to figure out a way to do that, so I could keep my Eggfinder antennae in the the bay without sacrificing performance.

And if I can expand on the OP's question, could someone explain half wave vs. quarter wave antennas? I think I understand, but I would really appreciate some clarification.

The curly thing is a helical GPS receiver antenna.

So as not to derail this thread, more photos of the AV Bay can be found in this thread:
https://www.rocketryforum.com/showt...uminum-charge-canisters&p=1583747#post1583747

 

[ksaves2]

The curly thing is a helical GPS receiver antenna.

So as not to derail this thread, more photos of the AV Bay can be found in this thread:
https://www.rocketryforum.com/showt...uminum-charge-canisters&p=1583747#post1583747

Yeah, The plastic cover was removed from the GPS antenna. I believe the term is it's circularly polarized and can maintain a lock better as long as the speed limit is not broken. Once the rocket slows down, it has the potential to reacquire a position
lock sooner. Gives one more data points to ponder. Onboard memory is a plus because positions can be missed over an Rf link but can be had once the rocket is recovered. Kurt

 

[ksaves2]

Here is what I have done in my Apache:
View attachment 303094
Details here if you want:
https://www.ausrocketry.com/forum/viewtopic.php?f=6&t=5019&hilit=apache&start=16

What is not visible in the picture is that the wire antenna is supported above the G10 fiberglass sled. Those are M5 nylon bolts, and the wire is fed through holes near the end of the screws, so the antenna sits about 15mm off the sled. That makes it more of an air dielectric and hopefully keeping it closer to the required electrical length. Proximity to the sled would slow down the EM waves due to the higher (~4.2) dielectric constant, making the antenna a little physically too short I think. Probably not a huge effect, but not difficult to do, so I did it. The screws are just threaded into tapped holes in the fiberglass.

You also can't see that the wire clears the metal parts at the tip by about 20mm.

Nice! That's a good way to do it with nylon hardware. On one of my nosecone mounts, I was able to trim off a forward portion of my press fit sled. I have an SMA antenna and didn't have to support a wire. I did some potting of the SMA connector in epoxy for additional support. The antenna is in the open space of the nosecone with no sled projecting up past the base. The Altus Metrum hardware works great with their wire antennas so nothing to gain by modifying them.

Kurt

 

[watermelonman]

It's not obvious that having different antennas with connectors is going to improve the signal much, if at all. You might be able to boost the antenna gain by a dB or so but that won't really matter much. The main reason to use connectors is if you need to have the antenna somewhere away from the radio proper.

Thanks for the perspective though the flexibility is still important. I am still at a loss for understanding how a single lead stick antenna can be replaced with a multi lead connector, which was my main question.

 

[mikec]

I am still at a loss for understanding how a single lead stick antenna can be replaced with a multi lead connector, which was my main question.

A typical antenna connector has the antenna lead and a ground that goes to the shielding in the cable. If you look at a board-mount SMA connector, the stuff that solders to the board is mostly for mechanical support of the connector and partly to tie into the board ground. You could ground it some other way.

As for why the connecting wire isn't an antenna, it's shielded; typically coax.

 

[caveduck]

A stick or "rubber ducky" antenna is a monopole antenna without a ground plane; hence only one conductor is used in the antenna itself. The big win is that the antenna is only half the length of a 1/4 wave dipole for the same operating frequency. Performance of these antennas is miserable because of the lack of a real ground plane, but at least they have the virtue of being mostly omnidirectional.

 

[mikec]

To be clear, when the OP said "stick" I don't think he was talking about a rubber ducky per se, but the 1/4 wave whip or wire antenna that is usually used on connectorless radio boards. The rubber ducky is shorter and base-loaded. All of these omni antennas basically have a gain of something like 2. If you want much higher gain you need to have some degree of directionality, usually in the ground station, because the rocket is pointing all over the place during descent.

We can now sit back and let the radio experts discuss what I've oversimplified.

 

[ksaves2]

To be clear, when the OP said "stick" I don't think he was talking about a rubber ducky per se, but the 1/4 wave whip or wire antenna that is usually used on connectorless radio boards. The rubber ducky is shorter and base-loaded. All of these omni antennas basically have a gain of something like 2. If you want much higher gain you need to have some degree of directionality, usually in the ground station, because the rocket is pointing all over the place during descent.

We can now sit back and let the radio experts discuss what I've oversimplified.

You are right. The issue with the 900Mhz band is a directional antenna along the lines of a Yagi, will have a narrow beamwidth and difficult to keep aimed at a rocket you cannot see. For the 900Mhz band, a patch antenna gives a modest gain
on the receive end with a broader beamwidth. This broader beamwidth lends itself for in flight tracking. With 2 meter, 1.25meter(the band the Com-Spec, Walton and Rocket Tracker are on) and 70cm bands the beamwidth of a Yagi is wide enough to be usable for in-flight tracking.

Once a 900Mhz rocket is down, a Yagi can be useful because the rocket is generally stationary unless blown by the wind and one can aim the 900 Mhz Yagi accurately. I've proven to myself that the ground foot print is increased quite a bit with
a Yagi in this case by doing antenna swaps while carrying out a recovery.

This can be considered if running a 900Mhz tracker say in the 100 to 250Mw range that is going to land 4 or more miles away. The farther away, the more important of an increased ground footprint. You get to the last known position and no rocket,
no new position received, you put on the Yagi and point it in the direction the drift pattern on your map suggests and head in that direction. You will pick up a new position much sooner than later with the Yagi.
Note: if the rocket lands in a topographic depression in the ground or behind a berm, you will have to get very close to the rocket or over the berm in order to receive a new position.

If one is going to be sport flying with the 900Mhz trackers, this stuff I talk of is likely superfluous but if one has it on hand, it can help in a bind. I picked up my Patch antenna for $18.95 and a Yagi for about the same. Don't think you can find a Patch for that much today but at the time, it was cheap enough for me to consider.

The only other way to increase range besides a more powerful tracking transmitter is to get licensed and use 2 meter or 70cm trackers on the Ham radio bands. 2 meters does better with longer antennas and would be perfect with large diameter nosecones
that have the length. You use 1 watt and you will likely to be able to receive a packet from a rocket 100 feet up in the air 5 miles or more away from you. Propagation on these bands is much improved over 33cm (900Mhz)

Does a sport flier need this?................. Naaaaaaaaaaaaaaaaaahhhhhh!! Several have flown entry level EggFinders to 20k and I daresay more with successful recoveries. I have done both types of tracking Ham/APRS and NMEA.
For sport flying NMEA is perfectly adequate. Kurt