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NSIFAQsRFSystems

FAQ Topics

RF Systems FAQ

1. I want my RF system to automatically switch between Tx and Rx mode. Can NSI provide this capability?

2. I have purchased a new RF cable with SMA(m) connectors, but have been unable to connect it to the Keysight 87301E coupler. What is the problem?

3.What RF connector types are compatible with each other, or can cause damage when mated?

4. Should I be concerned about ESD damage using long coaxial RF cables?

5. What is included with the NSI-PNA-20 system?

6. For harmonic mixing systems with AUT transmit and probe receiving, is it better to locate the harmonic mixer at the probe, so the lower frequency LO signal passes through the rotary joint, rather than the high frequency RF signal which might be up to 50 GHz? Wouldn't this reduce amplitude and phase errors induced by the rotary joint?

7. Are waveguide mixers better than coax mixers? When should they be used?

8. When using a stand-alone VNA, will the long RF cables limit system performance? Will additional amplifiers be necessary to improve SN?

9. Is the Panther receiver clock synchronized to the RF & LO sources?

10. What options are required to upgrade my PNA-X for pulsed antenna measurements?

11. Can I apply an S-parameter calibration while acquiring NF data with a PNA?


1. I want my RF system to automatically switch between Tx and Rx mode. Can NSI provide this capability?

Yes. NSI has designed systems that support automatic Rx/Tx switching and band-switching, as well as various antenna configuration modes..

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2. I have purchased a new RF cable with SMA(m) connectors, but have been unable to connect it to the Keysight 87301E coupler. What is the problem?

The Keysight 87301E is a 50 GHz coupler with 2.4 mm(f) connectors. The 2.4 mm(f) connector is not compatible with the SMA(m) connector. See FAQ #3.

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3. What RF connector types are compatible with each other, or can cause damage when mated?

Click here to see the frequency ranges and compatibility of different RF connectors.

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4. Should I be concerned about ESD damage using long coaxial RF cables?

We occasionally hear reports of customers damaging expensive RF equipment by electrostatic discharge (ESD). This note outlines a method for avoiding one common cause of equipment damage. A major cause of ESD-related damage is discharge from the center pin of a coaxial cable upon connecting it to some active device. A coaxial cable is basically a capacitor when the ends are left open. If the center conductor carries any charge, it will go right through your mixer, PIN switch, or network analyzer when you connect it. To avoid damage to expensive equipment, ALWAYS discharge the center conductor of ANY coaxial cable before connecting it to another device. To discharge the center conductor, use one of these methods:

1. Best Method: Connect a load to the cable first, then remove the load and connect to the device -- the charge will bleed harmlessly off through the load. Since most RF cables (and loads) are male, you'll probably want a load with a "barrel" adapter. CAUTION! Don’t try this on a cable that’s carrying any AC or DC power (bias voltages, etc.) or hazardous RF power levels.

2. Short the cable first, using a connector short, the mating connector’s outer conductor, the end of a torque wrench, or some other metal tool. If you use this method, there are several CAUTIONS that apply:
a. Don’t try this on a cable that’s carrying any AC or DC power (bias voltages, etc.) or hazardous RF power levels.
b. Make sure the cable isn't connected to some device that will be damaged by momentarily shorting the connected port.
c. When you touch the tool to the cable, contact the outer conductor first, then gently slide the tool to connect the inner and outer conductors. DON’T force a tool into the connector and bend or scrape the center pin!

Get into the habit of discharging cables before connecting them – help avoid expensive ESD damage!
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5. What is included with the NSI-PNA-20 system?

The NSI-RF-PNA20 RF System includes the following elements.

NSI-RF-PNA20-VNA includes:

* Keysight E8362B PNA Network Analyzer
* Keysight E8362B-014 Configurable test set option

NSI-RF-PNA20-SYS includes:
* Equipment rack
* RF cables and components
* Control cables
* Documentation
* 2 Year Warranty

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6. For harmonic mixing systems with AUT transmit and probe receiving, is it better to locate the harmonic mixer at the probe, so the lower frequency LO signal passes through the rotary joint, rather than the high frequency RF signal which might be up to 50 GHz? Wouldn't this reduce amplitude and phase errors induced by the rotary joint?

Yes, it is generally preferred to locate the harmonic mixer closer to the probe, however there are tradeoffs which must be considered that may be more important. If the mixer is between the probe and rotary joint, that means it must rotate with the probe, adding weight and mechanical complexity to the rotating probe carriage, and may require larger probe absorber coverage. Also, for systems with TX/RX reversal requirements, it is easier and more convenient to locate the mixer on the probe carriage where we may also mount a multiplier and directional coupler for the case where we are transmitting the high frequency from the probe. Regarding the RF performance, the effect of the rotary joint's phase wow on the signal will be the same whether the rotary joint is passing the LO or the RF signal, since any phase errors at the LO frequency are multiplied up at the mixer and will have the same overall affect on the resulting IF signal. The placement of the mixer between the probe and rotary joint can help reduce the signal sensitivity to the amplitude wow of the rotary joint, since the LO signal amplitude variation does not directly affect the resulting IF signal since the mixer is a non-linear device.

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7. Are waveguide mixers better than coax mixers? When should they be used?

Keysight and NSI coax mixers can be used up to 50 GHz, and are typically preferred over the waveguide mixers due to their lower cost and convenience of having a broadband device (typicallly 1 - 50 GHz). Keysight 's waveguide mixers have been discontinued; these used fairly high harmonic numbers resulting in high conversion losses. Above 50 GHz, waveguide mixers are the only solution.

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8. When using a stand-alone VNA, will the long RF cables limit system performance? Will additional amplifiers be necessary to improve SN?

Distributed RF sub-systems are often used to minimize the impact of cable loss within a given measurement system but may be more expensive than a single-box solution. Considerations for a fundamental mixing RF sub-system include examination of the system power budget to insure adequate system dynamic range. A broadband RF amplifier for budgetary purposes would be a wise precaution (see NSI RF Accessories, Amplifiers).

There are many factors which can affect the dynamic range including free space loss due to range length, cable attenuation due to cable length, dynamic range of the receiver, receiver IF bandwidth, gain of the range illuminator, and lowest sidelobe level of the AUT. These all have an effect on the RF subsystem power budget. As part of the RF sub-system design (once everything is known) the system power budget will determine whether additional amplification will be needed. (SG)

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9. Is the Panther receiver clock synchronized to the RF & LO sources?

The Panther receiver, as an IF receiver, is not synchronized, nor is it required to be synchronized with an external reference clock. As long as the Ref IF is 20 MHz, the receiver works as advertised.

The beam controller section, though not synchronized from an explicit reference signal, can be synchronous with external devices (and therefore those external device clocks). An example would be pulse mode. Measurements made in pulse mode are triggered off of the beam controler Input 4 (pulse edge), therefore the beam controller becomes synchronous to the reference oscillator of the pulse generating device. But still, the Panther internal clock is not synchronous to an external clock.

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10. What options are required to upgrade my PNA-X for pulsed antenna measurements?

NSI supports both narrow-band and wide-band pulse mode for the N522xA and N524xA. Narrow-band pulse options are 008, 021 and 025. No additional hardware is needed. Wide-band pulse mode is supported for any N522xA or N524xA with the addition of an external PIN switch for pulse modulation, and the NSI-RF-5501 Pulse Generator/Synchronizer. If the PNA has option 021 (internal modulator) then the external PIN switch is not needed.

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11. Can I apply an S-parameter calibration while acquiring NF data with a PNA?

No. Making measurements with an active calibration on the PNA is not supported. Measurements are transmission-only (S21), without calibration. The frequency response of the measurement includes the frequency dependencies of the probe, transmission loss and NF-FF transform, so it does not represent the frequency response of the AUT only. To measure AUT gain vs. frequency, perform a multi-frequency gain measurement using a standard gain antenna or calibrated probe.

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