Q: Does JRE Test manufacture custom sized RF Shielded Test Enclosures?
A: Yes, JRE Test will consider the customer’s concept and provide quotes for a new design with delivery of the custom enclosure typically within 8 to 10 weeks ARO.
Q: How do I choose the proper filtering capacitance of a D-Sub connector to guarantee the required data rate is passed into the RF Enclosure?
A. JRE Test currently stocks filtered D-Sub connectors that will pass data rates up to 1000 MBPS. A capacitance of 1000pf is used for data rates speeds up to 10 MBPS, 310pf for speeds up to 50 MBPS, 100pf for speeds up to 100 MBPS, and 10pf for speeds up to 1000 MBPS. Pin counts vary depending on the manufacturer of the D-Sub connector. Higher capacitance filter networks provide higher levels of shielding effectiveness.
Q: How do I allow high speed data into the enclosure while still stopping/shielding the RF signals?
A: This is a conundrum - allowing high speed data (which actually is nothing more than a 'specially' modulated RF signal) and stopping RF signals. Electrically and physically, this data and RF are essentially the same beast and there is no way of stopping one while allowing the other.
For example, one cannot filter the data lines on a RJ-45 LAN connector since that would capacitively load the data lines, and so severely distort and attenuate the signal that data communication would fail. One is trying to filter the RF from traveling along the same lines while allowing the data to flow unimpeded - and since the data is at RF speeds, we cannot do one without affecting the other! If one is able to use a very slow data rate, ie: 10 Mbps or so, a filtered DB-9 connector (100pf should be good) may be used with an RJ-45 adapter on each side. This allows the filtered DB-9 to attenuate the RF signals while allowing the (slow speed) data to pass somewhat unaffected (yes, the data lines will have 100pf dropped across them, but at slower speed, this should not be an issue).
As a point of interest, our filtered USB 2.0 does filter USB data lines using a special 1 GHz low pass filter, this allows the high speed data to pass through while stopping all RF signals above 1 GHZ - but, any RF below 1 GHz will easily pass through unimpeded! Since most device testing using USB interfaces is done using RF frequencies at 2.4 GHZ and above, this is no problem, but at cellular frequencies (800-900 MHz) the filtering provided by the USB 2.0 is minimal.
Q: Will the published Isolation Specifications be affected by the type of capacitive filter used for data or power connections into the enclosures?
A: Yes, the capacitance used in the filtered connector will determine the RF Isolation characteristics of the enclosure. Consult with JRE’s sales department to determine the best option to use for your application.
Q: Do JRE Test enclosures include properly engineered fan ventilation options?
A: Yes, all vent options include (2) ½” Nickel Plated cross sectioned panels that are tested to provide better than -115 dB shielding effectiveness @ 1 GHz and better than -95 dB shielding effectiveness @ 10 GHz. We use specially engineered 'honey comb' style filters which are both rugged and effective.
Q: Is it recommended to use shielded cables on all RF bulkheads and data cables?
A: Yes, using properly shielded cabling on RF bulkheads and data cables helps to guarantee the isolation characteristics of each RF Shielded Test Enclosure, ideally double shielded cable for best results.
Q: Are the hinges and latches field replaceable if they were to ever wear out from normal use?
A: Yes, all of the hardware used on JRE Test’s RF Shielded Test Enclosures can be switched in the field at the customers location.
Q: How often should the shielded gaskets be replaced?
A: It is recommended to replace the gaskets after 20,000 lid cycles or once a year. Replacement gasket kits are available for all of JRE’s enclosures.
Q: Can new connector options be added to an already modified enclosure?
A: Yes, the I/O plate used in most of the enclosures can be removed and sent back to JRE if new connector configurations are required for a new test application. The enclosure can also be milled to add new options in the future.
Q: I wish to use an Amphenol Mil style circular connector, will that affect the RF shielding isolation of my enclosure?
A: Be aware that while the connector body will allow a tight RF seal, the conductors transversing the connector will not have any filtering on them whatsoever – unless you find a connector that has such filtering built in, such as feedthru capacitors or the like. Any RF on your wiring can travel along that wiring and through the connector to the inside of the enclosure, this is a fact of physics. The carefully designed and manufactured, tightly sealed RF enclosure will be violated by connector pins which have no filtering, this is the reason we provide a wide variety of filtered connectors, feedthru capacitors and even specifically designed USB data filters.
Lest you give up hope of using mil connectors, in some instances, if your cable is shielded, any RF pickup will be found at the cable ends where the shielding stops - and if adequate precautions are taken, the shielding effectiveness of the enclosure and the unfiltered connector threshold can be usable in many applications. There is no way to accurately predict this since I am not privy to your physical test set-up, the frequencies involved, the RF environment or the effects that need to be mitigated. In general, if you are using a long cable of more than 4 or 5 feet, which is well shielded and grounded to the test setup equipment, and if there are no strong multi-watt RF sources nearby, you can expect 60 db of isolation and your tests may work. Bear in mind I am making a generality here for the purpose of helping you to understand the ramifications of this particular scenario, and I cannot give you specific figures or guarantees.
Q: How is the isolation specified?
A: Industry practice is to measure field strength at a distance of 1 meter from the device being measured (to ensure the measurement is in the far-field EM region and not in the near-field or transition-field region which can cause errors). To verify the isolation in the field, a signal source such as our HPSS-1 may be placed within the enclosure and a receiving antenna used to "sniff" the outside areas of the enclosure at close range, then a -20dB path loss factor is added to the close-in measured signal to reference back to the 1 meter distance. The 20 db factor is quite generous, it typically being in the 30 db range at the 2.45 GHz frequency of the HPSS-1. If one tries to measure the isolation at 1 meter distance, it is extremely hard to measure since the isolation of a JRE Test enclosure is so darn good!
Q: Do you supply any certification and test results for the shielding effectiveness?
A: Upon request we can provide a Certificate of Conformance with any enclosure. Of course, after manufacture, we test each enclosure to verify that they meet our specified isolation, but do not individually log or document any of the test measurements made on a particular enclosure. If you wish us to document our tests on your particular enclosure, we can do this for you at an additional cost based upon standard engineering billable time. This time would be determined by your requirements and we would need to know exactly what you would like us to measure and in what fashion.
Q: Regarding the shielding isolation, how flat is the response?
A: I am particularly curious why one would need to know isolation 'flatness'. For example, the JRE1724 is specified to provide a minimum isolation of at least -100db at 1 Ghz. What difference does it make if the isolation varies from -107 to -123 over this range, provided it is better than our specified -100db? If you do indeed need to know the enclosure's isolation at exact and particular frequencies, we can measure this for you at an additional cost as outlined in the FAQ above.
Q: How effective is the test enclosure at very low frequencies?
A: At low frequencies, the RF isolation of all our enclosures approaches the -100db level as detailed on each enclosure, with the actual isolation being dictated more by the I/O interfaces used. This is because at these low frequencies, leakage occurs in conducted emission on cables crossing the enclosure's RF shielding barrier.
An RF signal propagates via changing E and H fields and the enclosure effectively 'short circuits' the E field, thus providing the isolation. Note that the H field, which is magnetic, is not shielded due to the enclosure walls being constructed of a non magnetic material, i.e. Aluminum. So, if your signal is a magnetic only signal - visualize that as transformer coupling where the primary coil couples a magnetic field to a nearby secondary coil - you will experience limited magnetic only isolation.
Article such as key-fobs and the sort utilize RF signals which, of course, would be highly shielded. The enclosure itself provides shielding isolation beyond practical measurement at these low frequencies.