After examination of several NMO Mobile Mount Options in a previous post, I shrunk the field to two choices: a 3/8″ and a 3/4″ inch both from Laird.
I had occasion to test four popular amateur radio mobile antennas. Here are the results of SWR and Return Loss of a Diamond SG7900ANMO, Larsen NMO 2/70, Cushcraft CS-270M and Laird QW144.
For years I have had great success with my trusty no-name mag mount 2m/440 mobile antenna. However, it’s time to consider a permanent through-hole NMO mount. NMO product information is a bit misleading so I bought several varieties to figure out the details. I share the results below.
Mag Mounts. Bum Rap?
Over the years I have heard amateur radio folks, CBers and scanner fans bash the use of magnetic mount antennas. Concerns include flying off the vehicle and becoming a projectile during an auto accident. Other concerns relate to performance and stem primarily on how well the shield of the coax is electrically connected to the conductive body of the car.
I cannot comment on the mechanical realities of the antenna flying off the roof during rapid changes in speed, but can say I have never seen one do so. I encourage anyone with data to propose their article to this web site
Addressing the Mag Mount Electrical Questions
Let’s talk about the electrical conductivity of a standard mount vs. a magnetic mount antenna. Here is a quote from the newsgroups concerning antennas for scanners…
In the never ending quest to improve our HF mobile ops for the Virginia QSO Party we finally decided to try a small loop.
There is nothing new about small loop antennas. They have been discussed in the literature for decades. The ARRL has some very old articles about them in the 1968 March and July editions.
Constantine A. Balanis’ book on Antenna Theory discusses and defines large vs. small loops. This book is an essential reference if you seek the details on how loops work. The loop described below fits into the “small loop” category where the currents along the conductor are, for all practical purposes, constant. This is unlike full size antennas where current reaches a minimum where voltage approaches maximum. Since this loop is electrically short with respect to wavelength, current does not change “much.”
Your forked over $13 to take the test (some VEs charge nothing… shop around). Perhaps you forked over another $13 for another chance… It happens.