I have been checking in daily to see the latest mods and range testing of the goTenna Mesh.
It is now time to build one of my own and spread the mesh goodness.
Since I will need a bunch of help and guidance, I thought we could build one together.
Which Yagi Antenna? I live in a mid-rise condo and the MOAN will be placed on my balcony. No use for an Omni Antenna as the signal will not go through the building. What beam width would be best? I am on the 14th floor. Thinking one of these two: ZDADJ928-11YG and ZDADJ928-8YG. 902 - 928MHz yagi Antennas
Where do I solder the Coax to the goTenna? Do I drill a hole to disconnect the goTenna antenna?
I am consolidating a bunch of links and images below that will hopefully help get to the bottom of exactly where the center of the coax should be soldered to. (I know @canmoose2 and @ShootAnyAngle along with many others have had similar questions.)
The goTenna is set to select the RED capacitor which is connected to the Fractal antenna. In order to select the Green output, the RF chip needs to be switched by applying a voltage to a pin on the chip and removing the voltage from the pin that has selected the RED output. I cannot say which pins are involved but if there is a data sheet available it can be determined. That would allow the RF path to be directed to the MMCX center pad which is where the connector is being attached. Simply cutting the circuit board to break the path to the Fractal would be easier (my opinion) and soldering the center of the coax to board where you made the cut, The coax shield would simply be soldered to the ground nearby. I am not sure if bypassing the capacitor would make an improvement or not. If so, you could carefully put a solder blob across it.
Good luck…Ken - W4KLP
Kotuku…Yes this is correct. However, would make the cut a bit closer to the first vertical turn of the circuit board.
The closer you can get to the capacitor is better but be very careful as things get a bit like brain surgery and you don’t want to say “oops”.
The purpose in doing this is to allow you to replace the fractal antenna with a external higher gain antenna which will give your Node more service area. Adding an external antenna without disconnecting the internal antenna will cause problems with performance. The RF impedance of the antenna is around 50 ohms. If you paralled the internal antenna with a 50 ohm external antenna, the impedance of the load would be near 25 ohms which would be a mismatch and cause a loss of performance.
As a suggestion for a high gain omni antenna, look at the Comet KP-20. This may be a problem in some cases as it is 8 feet long. The gain is around 9db and is fairly inexpensive at $110. It can be purchased from The Antenna Farm. I am considering ordering one.
Ken - W4KLP
Sounds really nice! Omni antennas are good if you live in the center of a lot of users in all directions, however the yagi works great if you need to cover a sector which depends on your particular location. I would make it vertically polarized. If you are linking to another node that is aiming at you be sure that you both use the same polarization or you could have a 20db loss of signal between you.
Ken - W4KLP
For adding an external antenna…
I checked with engineer at gotenna and he recommended bypassing the capacitor (C-50) by either removing it and solder across the gap or simply put s small blob of solder across the top of the capacitor…this is how I did mine and I think it would be easier and have less of a chance of messing something up on the board. Use a good magnifier or microscope if you have one.
Ken - W4KLP
This looks good to me! This is a better way to attach an external antenna due to not having to bypass anything on the board per-say. I fried a unit and after that I decided that this would be a better way to go. Also keep the runs of coax short! Loss goes up a TON the longer the cable you have is. That’s one reason the MOAN works so well is because the total length of coax is 5 (maybe less) inches.
@Ken what do you think about the advice I have above?
Good advice on the coax losses, I used a small diameter Teflon jacketed coax with SMA male about 6 inches long, I slid the gotenna (removed from case), up into the mounting pipe for the Comet KP-20. I send 5 volts up the mast to the gotenna with a long length of single pair cable. The gotenna is in Relay Mode, It relayed my signal from a parking lot about 3 miles away to my wife’s gotenna in the house. Haven’t tried it farther away but I will soon. An.tenna is 60 feet high
Ken - W4KLP
I also think that going off the antenna is a better idea as far as SWR goes. Off the antenna you’re going to get 50 ohms (or very close to it) and SWR is of course important for antenna and power efficiency. A mismatch is no good. Short runs of coax and making sure you’re getting 50 ohms seems like a plan to me!
Bypassing/Shuting the C-50 capacitor is needed if an external antenna is installed as the capacitor is there to adjust the impedance of the on-board fractal antenna to match the 50ohm nominal impedance output of the RFFM6904 (RF Transfer Switch)
Add-on antennas would have their own impedance designs (be sure they are set for 50ohms) and any cabling between the antenna and the GTMesh should also be designed for 50 ohms. This will help to keep the VSNR (voltage signal to noise Ratio) low, preventing TX signals from bouncing and returning back into the radio) Any signal bounced back into the radio is not transmitted power and can cause the radio to become damaged.
This is why using super low cost antennas with wide bandwidth ranges can be bad. The VSNR is not tuned to the 900 Mhz ISM band and can cause excessive heating or damage to the radio.