Ask Harlan, December 22, 2006

From: Chandrakanth Mariyappa, L&T

Dear Harlan,
How can I calculate the minimum detectable signal (MDS) of a receiver chain using a spectrum analyzer? What things need to be considered during the calculation?

Dear Chandrakanth,

The way to determine the MDS is to monitor the output noise level of the receiver. Apply a signal at the input and determine the level needed to see a change at the output. This will be the MDS.

From: Bassem Okaily, Lebanon

Dear Harlan,
I have a fly-away Ku-band digital. If I want to change it to HD, do I only need to change the encoder and what is the minimum bandwidth transponder to transmit the HD signal? Could you help me learn more about HD transmission?

Dear Bassem,

I am sorry, but your question is a communications systems question that is outside my area of expertise. I am afraid that I cannot help you.

From: Glenn Vitale, Georgetown University Medical Center

Dear Harlan,
What is the safe exposure rate for microwaves during an eight-hour work day?

Dear Glenn,

The safe exposure rate is dependent on the frequency that affects the SAR (specific absorption rate). There is a recently updated version of the ANSI-C-95 safety standard, which is available from the IEEE at www.ieee.org. It has detailed information that should answer your question.

From: Eric Thomas

Dear Harlan,
Where can I find a jammer or other simple device to block the effects of voice to skull (V2K) or the microwave hearing effect? Is it possible to use another jammer (a cell phone jammer, for example)?

Pulsed RF fields: Exposure to very intense pulsed RF fields, similar to those used by radar systems, has been reported to suppress the startle response and evoke body movements in conscious mice. In addition, people with normal hearing have perceived pulse RF fields with frequencies between about 200 MHz and 6.5 GHz. This is called the microwave hearing effect. The sound has been variously described as a buzzing, clicking, hissing or popping sound, depending on the RF pulsing characteristics. Prolonged or repeated exposure may be stressful and should be avoided where possible.

Dear Eric,

There are no jammers available that will cancel radiated power and the civilian use of jammers of any kind is against both FCC regulations and the law. The effects that you quote are controversial and are not widely accepted as scientific fact. Reports of experiments claiming to create these effects have indicated that the power levels used are so high that other concerns are far more important.

From: Dan Grafflin, S.S.T. Data Systems/RD

Dear Harlan,
Where can I find technical information or data sheets for obsolete components, such as Qualcomm's Q0256 FEC decoder, Conexant's CX24110 QPSK demodulator and Broadcom's BCM4500 QPSK demodulator. Is this information available on-line?

Dear Dan,

I do not know if there is anything on-line; however, if you check old copies of Electronic Engineer's Master Catalog (EEM) you can probably find them. EEM is published by Hearst Business Communications Inc. in Garden City, NY (516) 227-1300.

From: Manu Gaurav, DRDO

Dear Harlan,
In spectrum analyzer measurements, when I am changing reference level, I find some spurious appearing. The spurious level is also fluctuating with reference level setting. The signal input is 13 dB less than prescribed, the maximum limit of a spectrum analyzer. The input to the spectrum analyzer is 0 dBm. Is it necessary to keep the reference level more than the input signal level? Could you explain this phenomenon? I am also open to the idea that the spectrum analyzer is bad, but this spectrum analyzer was purchased by my company 10 days back and this problem appeared during the acceptance checks.

Dear Manu,

I am afraid that I do not have enough information to answer your question. I suggest that you contact the manufacturer of the particular spectrum analyzer that you are using.

From: Mostafa Abdolhamidi, Iran Telecommunication Research Center

Dear Harlan,
I am a microwave engineer and I have found ADS the first choice to simulate circuits. However, some time ago when I used it to run an optimization process (actually when I export a layout component and call it in an optimization process in the schematic environment), after some iterations, with a "segmentation violation error," the process ends. Could you provide any insight into this?

Dear Mostafa,

I am sorry but I am not an expert on the interactions of ADS. You need to contact the people who supplied the software.

From: Zubair Ahmed, National University of Sciences and Technology

Dear Harlan,
How can I find a paper cited in old issues of Microwave Journal, including: 1) "A General Design Procedure for Bandpass Filters from Low Pass Prototype Elements: Part 1," December 2000 and 2) P.N. Richardson and H.Y. Lee, "Design and Analysis of Slotted Waveguide Arrays," 1988 [109-125].

Dear Zubair,

Papers that are too old to be in our electronic archive are available as hard copies. If you will provide us with your mailing address, we will send them to you. There is no charge for this service.