As we mentioned in previous posts, before we submit product to compliance house for full testing, we should first contact compliance test house for a pre-compliance testing, to find out and make corrections if there are obvious power level or harmonics that doesn't meet regulatory requirements, but before that, we also have to do a in-house testing here in factory as manufacturer, the in-house testing is not so accurate as in test labs, but it also helps sort out some major issues before handling product to customer.
There are other ways if you don't want in-house testing prior to submit to compliance house, for example, you can hire a consultant experienced in compliance testing like FCC ID or CE R&TTE, or you can use a reference design provided by many chip providers that already tested in labs, so you can expect the result is somewhat near, but usually you'll need to do some adjustments thereafter, and you should just use the same circuit board layout and material, with proper parts model, sometimes the board size is limited and you'll need to change the layout, which will cause dramatically difference in testing results.
We always recommend customer do a in-house testing, since it is possible in most circumstances, it doesn't need fancy instruments to carry, what we need is basic RF instruments like spectrum analyzer and matching antennas, and better if you have remote control transmitter that already passed FCC ID, which can be used as reference in transmit power reading using spectrum analyzer.
To do a in-house pre-testing of remote control transmitter, first we would need to prepare our test equipment, which can be found as follows.
- spectrum analyzer covers the given range
- amplifier, 100Mhz to 5Ghz, 20dB gain and -60dBm input
- antenna to cover 100Mhz to 5Ghz spectrum
- insulating tripod to support the antenna
And there are also some requirement about the working environment for in-house pre-testing, as follows
- since we will need to do 3 meters radiation test same as compliance house, so we will need a open-space for this, and also 1 meter radial space of the antenna and product to be tested
- testing space must also not be interferenced by other radio emssion source, such as RF remote control transmitter other than tested, motors etc.
- floor area should be covered by layer of ground plane, using copper or aluminum
- test subject is to be placed on testing table, which should be made of plastic or wood, which means it just used to support test subject at given place, and by no means should it interfere the RF radio radiation and signals
- always keep antenna at certain orientation is very important, for example, horizontally orienting antenna will ploarize in such a way that errors due to ground reflections are reduced
The above points should be considered as minimum in-house testing setup, please also note since test environment is no way like in compliance labs, so reading on spectrum analyzer is different than what you will get in compliance testing labs, the margin in-between is around 10dB to 15dB, because the typical compliance lab setup is like above photo, all RF signal emitted by test subject will be collected by antenna, so that's why you'd better prepare a reference DUT that already passed FCC ID, to check the values as reference.