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Well I've been building and flying or driving radio controlled models for over 40 years and during that time I like to think I've built up a reasonable amount of knowledge.

I'm also a qualified electronics engineer who has worked in radio frequency, analog, digital systems and software for more than three decades. In fact I designed and built my first RC set back in 1969.

For the past nine years I've also been involved in the design and manufacture of some rather sophisticated engine technology and UAV flight control systems.

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RC explained: Demystifying terms such as PCM, PPM dual conversion, single conversion, full-range etc., this feature will explain it all.

Cheap Chinese Engines: Just how good are those cheap Chinese glow and gas engines that sell for half the price of their "brand-name" equivalent? I put several to the test.

Build your own radio gear?: Back in the old days, building your own RC gear was not uncommon and now the arrival of 2.4GHz has made it practical again.

 

Review: HobbyKing 900MHz FPV video system

CHEAP BUT LIMITED

Dated: 6 May 2011

One of the key components (some say "the" key component) of any FPV setup is the video system that transmits the video image from your model to the ground.

To date, I have been using the FoxTech 200mW 5.8GHz video transmitter and receiver to do most of my FPV testing but in this review, I'll be looking at the 200mW 900MHz system sold by HobbyKing for a surprisingly low price.

What's in the box?

The system comes packaged in a tidy cardboard box which contains the video transmitter, the receiver, a pre-configured wiring loom for the airborne side, a cheap AV lead, a cheap color camera, and two sleeved dipole antennas.

The first thing most people will notice, when comparing this system to a 2.4GHz or 5.8GHz one, is that the antennas are huge (and heavy). As the frequency goes down, antennas tend to get larger -- since hey have to deal with a longer wavelength of signal. In the case of the HK 900MHz system, the transmitter antenna really is too big and heavy for anything smaller than the Skywalker or HK EPP FPV models. These antennas are also far from well-matched to the transmitter, resulting in lower range and higher operating temperatures than would otherwise be obtained.

The lack of a bayonet connector and power-lead for the receiver seems to be an odd omission, especially given the thoroughness of the wiring on the transmitter end.

The quality of construction is satisfactory and the inclusion of the pre-wired loom for the airborne end is a big bonus for those who consider good soldering to be one of their weaknesses.

The transmitter end is configured to run of a 3S lipo without the need for an additional UBEC or regulator -- that's good. Even the camera will take the full 11.1V of such a setup.

On the receiver end you'll have to find yourself another 3S lipo and one of the barrel plugs which connect to the receiver. Be careful, there are quitea few different sized barrel plugs with different sized holes. Make sure you get one that is the right size or it will either not fit or will be intermittent in operation.

The Camera

If you're serious about FPV you'll ditch the cheap camera that comes with this system.

I tried the NTSC and the PAL versions, neither was really good enough for flying in anything other than perfect lighting.

The PAL version had a foggy haze that adversely affected contrast and the NTSC system, although not so badly affected, was unable to handle high levels of contrast between sky and ground without blooming and losing detail.

It's worth remembering that when you fly FPV, the camera is your eye so skimping here is not such a good idea. There are plenty of good FPV cameras available for under $100 so shop around if you want to improve the overall performance of this system.

The RF system

Given the excellent performance I was able to achieve from a 5.8GHz system, I expected that the 900MHz would be even better, at least in terms of range.

Unfortunately, that was not the case.

During test flights I found that there were noticeable signal dropouts at distances of just 1KM (1100 yards). It was possible to "fly through" these signal losses but then I discovered another unpleasant effect of this 900MHz system...

At distances beyond about 1.2Kms, my RC system began falling into failsafe. At first this was intermittent but, by the time I reached about 1.4Kms, the failsafe had fully kicked in.

What was going on? In tests with the 5.8GHz system I'd repeatedly flown exactly the same RC system out to beyond 2.2Kms with no sign of any failsafe conditions. Why was my RC system now delivering only half that range?

Back at the workshop I threw the 900MHz system on the test-bench and found that it was creating enough noise on the 2.4GHz band to effectively mask the RC signal at longer distances. By comparison, the 5.8GHz system was clean.

The 900MHz receiver also seems to have a rather low sensitivity, a factor that compromises peformance quit a bit.

This all indicates that the system has definitely been "designed to a price" rather than with best performance in mind.

On the other hand -- it is cheap as beans so once again, you get what you pay for.

When time allows, I'll be adding a notch-filter to try and reduce the amount of spurious signal it outputs onto the 2.4GHz band and we'll see whether that restores some of the lost RC range.

In the meantime, despite having the same power as the 5.8GHz system, I'd have to say that this is a "close range" FPV system for those using 2.4GHz RC equipment. If you're running the old "long-wire" PCM/FM gear you may get more range because the amount of noise generated on frequencies below 100MHz seems to be much less.

A few words of warning

Although it's billed as a 900MHz system, the transmitter and receiver can actually be configured to work on much higher frequencies and on parts of the radio spectrum that are not legal for such use.

All but the bottom quarter of the 900MHz band, for example, are reserved for aviation use. Systems such as secondary radar, collision avoidance and other things are entitled to use these frequencies so if you're caught broadcasting an FPV signal on them you could end up in very big trouble.

US users can safely use channel 1 because that falls in their ISM band but in most other countries, this channel will interfere with GSM mobile phone services.

I will soon be looking at how these systems can be reprogrammed to use different frequencies within the 900MHz-1.1GHz band that may be legal in various locations. Stay tuned for that.

Summary

If you're in the USA and you're just looking to give FPV a try at the lowest possible cost then it's probably worth laying out the asking price for this system so you can decide whether FPV is for you -- without spending more than have to.

Don't expect too much though.

However, if you've already decided you're going to get into FPV then I'd look for something that doesn't have the drawbacks and limitations of this low-cost system.

Pro's:

  • it's cheap
  • pre-made wiring loom makes it easy to set up
  • will operate from a 3S lipo

Cons:

  • may reduce the range of your 2.4GHz RC system
  • may affect the operation of your GPS (if fitted)
  • camera is pretty crappy
  • may not be legal in your part of the world
  • stock transmitter antenna is too big/heavy
  • poor performance overall
  • only a single video-out connector on the receiver
  • Product: Hobby King 900MHz 200mW FPV system
  • Purchased from: LotusRC/HiModel.com
  • Price: around US$50
  • Overall rating: 2.5/5

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