Review: RMRC 1.3GHz 400mW VTX Video Transmitter

Is this possibly the most popular 1.3GHz VTX for long range flying on a fixed wing and plane? Let’s check out the 1.3GHz 400mW VTX from ReadyMadeRC.

Where to Buy?

Many thanks to ReadyMadeRC for sending the VTX in for testing! You can buy it from:

Why 1.3GHz? Why 400mW?

The low frequency of 1.3GHz has better signal penetration ability than 5.8GHz, and therefore more suited for long range FPV. There are pro’s and con’s using 1.3GHz vs 5.8Ghz as discussed in this article, so I won’t repeat here.

You don’t really need a lot of power to fly long range on 1.3GHz. According to an unverified claim, 15 miles was achieved on 400mW even without breakup (using Mad Mushroom antenna on VTX, Pepperbox antenna on VRX). What?! 15 miles isn’t enough? Have you even thought about the amount of walking if you crash? :D

You could certain use higher power VTX, but there is a higher chance causing interference to other components, e.g. your radio receiver and GPS. It’s important to use just the right amount of power for what you need. Using more than you need can actually be bad when it comes to VTX.

Specifications

There are two versions you can pick depends on your region: US and International (for the rest of the world). The only difference I can see in the specs is just the channels they support. Oh, and the color of the case too.

The US version is green, and the available channels are:

  • 9: 1280MHz
  • d: 1258MHz

The International version is blue, and the available channels are:

  • CH4:1080MHZ
  • CH5:1120MHZ
  • CH6:1160MHZ
  • CH7:1200MHZ
  • CH8:1240MHZ
  • CH9:1280MHZ
  • CHH:1320MHZ
  • CHC:1360MHZ
  • CHd:1258MHZ

The one I am reviewing is the International version. It’s important that you understand which one you are getting, and that your receiver has the matching channels.

Looking for 1.3GHz video receiver? This is a good one: http://bit.ly/rmrc-1-3ghz-receiver.

In the package you can find the transmitter, a dipole antenna, and AV cable as shown:

The weight I measured is much lighter than advertised:

  • VTX Weight: 58.1g
  • Antenna Weight: 17.3g

It takes DC 12V as power (okay to be powered by a 3S LiPo directly), and current consumption is around 0.7A.

It uses SMA antenna connector. There is button next to the SMA, which is used to change channel. That’s about it, as simple as it can get :)

Closer Look

The RMRC 1.3GHz 400mW VTX comes with a huge blue heatsink case. It can be removed for a lighter and smaller form factor.

However if you do remove the heatsink/case, make sure you have good airflow to the VTX to avoid overheating.

To remove the case, simply take off the four screws on each side. You will also need to peel off the digit display protector with a slot screw driver. And the VTX slides right out.

The weight saving is massive!

  • Weight without case and antenna: 22.3g (from 58.1g)
  • Weight without case, with antenna: 39.5g (from 85.4g)

The 1.3GHz dipole antenna is pretty big and heavy, that’s why you don’t see people using 1.3GHz in Mini Quad.

Power Testing

I tested the RMRC 1.3GHz 400mW VTX with the ImmersionRC RF power meter V2. Every measurement was taken 10 seconds after the VTX was powered on, and the VTX was allowed enough time to cool down before the next measurement.

CH4:1080MHZ 264
CH5:1120MHZ 280
CH6:1160MHZ 301
CH7:1200MHZ 309
CH8:1240MHZ 313
CH9:1280MHZ 304
CHH:1320MHZ 303
CHC:1360MHZ 300
CHd:1258MHZ 307

The results suggests this is more of a 300mW VTX rather than the specified 400mW. But still, 300mW should give you some serious range on 1.3GHz as long as you are using the right antennas :)

3 thoughts on “Review: RMRC 1.3GHz 400mW VTX Video Transmitter

  1. Wingspinner

    One last comment on this antenna topic I fails to mention in my previous post… Such a “rubber ducky” antenna could also be a “sleeve dipole” created by running the coax feedline through a brass or copper tube of correct length, terminating the shield at the far end of the shield and then extending the center conductor the correct length past the tune. It’s a simple way to create a vertical dipole but the impedance does not match the standard 50-52 ohm coax and transmitters commonly used. As well you’re still feeding a “balanced” antenna with unbalanced feedline which creates problems with the coax shield becoming conducting RF back to the TX and SWR being very sensitive to length and proximity to other components. A well designed sleeve Dipole will have a coil at the bottom often made from the coax itself to improve the impedance difference and diminish the negative effects of feeding a balanced antenna with coax. However on such tiny antenna it’s very difficult to creat the required coil in such a small antenna and most of these small antenna don’t have one (none that I’ve disassembled). As a result much of the TX RF is wasted being reflected along the shield of the feedline coax. Bottom line: very inefficient and poor performance. So perhaps we his antenna is a sleeve dipole and is correctly labeled as “dipole” however much, much better performance (range, quality) will be realized with a cloverleaf, patch, or even a standard dipole (with a BALUN and proper feedline orientation).

    Anyhow, apologies for the length and number of posts here but to get good performance it’s important to know for sure what kind of antenna you’re hooking up to your TX so you can use what’s best for you knowing the cost performance tradeoffs. Hope I helped rather than confused!

    Cheers,
    Wingspinner

    Reply
  2. Wingspinner

    In the last paragraph where I mentioned creating a “groundplane” from the metal in the vehicle I made a type and wrote dipole and should have written monopole.

    Thx
    Wingspinner

    Reply
  3. Wingspinner

    Hello,
    I’ve seen several advertisements and posts calling the black “rubber ducky” antenna in your photo a “dipole” antenna. While it could be a “vertical dipole” it’s performance will be very poor due to the feedline not being perpendicular to the radiators, in close proximity to one of the radiators and being fed from a coaxial feed line therefore it’s almost certainly an end fed monopole. If it’s a good monopole it may be of the co-linear type which have more gain horizontally but more than likely it’s just a tuned single wire monopole.

    What’s the difference? A true dipole has two horizontally opposed radiators one half the frequency wavelength in length (hence the “Di” in dipole) where one side of the feedline is connected to one radiating and the other side is connected to the other radiator. As a dipole is a balanced antenna requires what is called a BALUN if used with coax feedline to work properly. A monopole is simply a single radiator connected to the center conductor of the coax feedline with the braid ideally going to ground (as in a copper rod pounded into the ground or in the case of a vehicle, a “ground plane” made up of the metal in the vehicle. Scientifically a monopole is a very inefficient form of a dipole with ground being the poor replacement for the second radiator but we don’t call the “dipoles” since they really only have one radiator.

    If you have at least a quarter wavelength of metal surrounding a dipole to form a good groundplane the can be pretty good antenna with a low radiation angle but usually that’s not the case. If you want to read more about it check this Wikipedia article – en.m.wikipedia.org/wiki/Dipole_antenna

    Reply

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