Ask Harlan, April 4, 2006
Published April 4, 2006
From: Dimiter Petrov, Communications Regulation Commission for Bulgaria
I am in the process of creating a homemade BC filter in 430 mc. I have several pieces of 3 and 1/8 coaxial cable. Because the outer pipe is a "harmonica" type, could you advise which inner diameter will work for calculation? Also, I need to work with this pipe for a 1/4 lambda transformer to match my two yagi-antennas. Each is 50 ohm. With the same inner diameter, I need to calculate a transformer with 35.4 ohm. Is the formula Z=138xLog (D/d) enough or do you have a more accurate formula?
If by "harmonica" you mean that the outer conductor is corrugated, you can determine the effective diameter by working backwards from the known impedance of the cable and use this value to calculate the transformer.
From: Saeed Saimh, Bayanat
Could you define null depth and where I could find information regarding this topic?
From: Xie Maoxu, ZTEIT
I am involved in a project of a CDMA 450 MHz PCMCIA datacard. The spurious EMI of the notebook or PC with the card plugged in always causes interference in the 450 MHz band. The coupling sensitivity of this terminal is down to -95 dBm while the conducted sensitivity is -110 dBm. How can I reduce the effect of the spurious EMI and improve the performance of the coupling sensitivity?
From: Craig Aarseth, Telephonics Corp.
Who makes the locking TNC connectors that appear in the March 2006 cables and connectors supplement of Microwave Journal?
From: Salman Ateeque, Ericsson
What is an adaptive time domain equalizer (ATDE)? What is its use in microwave radio communication equipment?
From: Douglas Wong, Raytheon
I am looking for design information on a 9-way power divider in stripline medium. Also, I have your early edition of Stripline Circuit Design. I could not verify calculations of equations on unequal power dividers with charts in the book. Do you have a revision?
From: Saeed Saimh, Bayanat
Some lightning rods have a tow side (protection and un-protection). What is the right method to fix it at the IF cable and what problems may occur if I fix it in the wrong direction?
From: Hussam Al-Zaaterah, Aces
Could you tell me what happens if we put two transmitters near each other? The first one is 2.4 GHz at 10 dBm and the second one is 5.6 GHz at 40 dBm output power. If we switch on both transmitters a high bit error rate (BER) occurs.
Dear Hussam, I cannot be sure since I do not know your receiver characteristics. However, I suspect that spurs and harmonics from the two transmitters are getting into the receiver chain. You might check the transmitter outputs to see how clean they are.
From: Faisal Khan, Giki
What is magnetic resonance?
Dear Faisal, Magnetic resonance is a very complicated phenomenon, which is difficult to explain in a few words. Basically it is based on the spin or precession of the nucleus of an atom. In a strong magnetic field the protons of these atoms can be aligned. When an RF pulse is applied some of the protons will absorb the energy and will precess in a different direction. This is the resonance. There is a good eight-page paper explaining the theory called "Nuclear Magnetic Resonance Spectroscopy - Theoretical Principles" that can be accessed on-line at www.shu.ac.uk/schools/sci/chem/tutorials/molspec/nmr1.htm.
From: M. Doshi, Syracuse University
I am in the process of designing a fixture for a filter. It uses a pogo pin of varying diameters and lengths. I calculated the outside diameters of the fixture based on the characteristic impedance of 50 ohms, given lengths and diameters of the pogo pin. Now, at the discontinuities there is an impedance mismatch problem. How can I solve this problem?
Dear Mr. Doshi,
I am studying the wide angle impedance matching and scan blindness in microstrip antennas for electronic scanning using IE3D software. I would like to use a waveguide simulator for this purpose. Though waveguide simulators are well established for open ended waveguides and other similar structures, I am at large in using the same as far as the microstrip antenna. This is due to the presence of a dielectric substrate. Does the size of a waveguide (simulator) also depend on the dielectric constant? Are there any articles discussing the use of waveguide simulators for infinite array studies on microstrip antennas?
Harlan Howe, Jr. received his BS degree in optics from the University of Rochester in 1957. He has been actively engaged in the microwave industry for 48 years, first as a design engineer and then as an engineering manager. In 1990 he became the publisher/editor of Microwave Journal. He retired as publisher in 2001, but remains the editor. He is a Life Fellow of IEEE, past president of MTT-S and the recipient of an IEEE Third Millennium Medal in 2000 and the MTT-S Distinguished Service Award in 2005.