At Contest University 2008 the importance of this book was again stressed, and a discount coupon to buy a copy was part of the CU packet. Here is my write-up & review of the book from 2007. It is also being reposted as it was done before Tags and RSS feeds were implemented for this blog.
At Dayton 2007’s Contest University one book on the important issue of station design for Multi Stations and SO2R (Single Operator Two Radios) Stations was mentioned by several of instructors.
Managing Interstation Interference by W2VJN
During the Dayton show I made a beeline to the INRAD booth to buy three copies – one for my local club, one for my Dayton traveling partner George W9EVT and one for my amateur radio library.
I found George W9EVT speaking with a long lost old time High-Speed CW contact who had worked Skeds for years between them. Imagine my surprise to find that with the books fresh in hand that this CW expert was none other than George W9JVN – Author of the Books!!
I mentioned how this book had received multiple mentions and recommendations during the Contest University and how I appreciated meeting the Author in person.
From the introduction of the book:
Whenever two or more transceivers are used in close proximity there is some level of interference involved. This level can vary from practically no problem to actually burning up components in the receiving radio. The purpose of this book is to identify and quantify the various parameters that create the interference and to show methods that will reduce or eliminate it.
My read of the book since Dayton has found that the CTU Profs understated the quality and usefulness of the information in this book. And that the book has not gone unnoticed by other experts:
“George [W9JVN] covers every imaginable
aspect of the interference
problem in this book…”
The actual stubs can either be designed and made by the amateur themselves, or one of George’s other businesses Top Ten Devices offers W2VJN’s Stubs as a commercial product:
Band Reject Coaxial Stubs
Every multi-transmitter environment suffers to some extent from harmonic interferences. In some cases, coupling due to closeness of antennas is sufficiently high that potentially damaging voltages may be present at the receiver terminals. Harmonics can be so strong that operation within 25 or 50 kHz is not possible due to receiver overload. Application of band reject coaxial stubs will reduce transmitted harmonics from the final amplifier and reduce fundamental pickup as well. This translates to fewer complaints from the operators, higher contest scores, and reduced risk of receiver front end damage.
Approximately 30 dB of harmonic attenuation can be expected from a single stub. Lumped constant filters can also provide the mentioned benefits, but none are available for amateur use unless they are home built. Top Ten Devices uses high quality RG-213 coax with a silver plated, teflon PL259 and heat shrink tubing on the shorted or open end. Rated ultra-conservatively at 1.5 kW continuous duty operation, these stubs will last a lifetime.
Stubs are manufactured to order and are individually trimmed with a Hewlett Packard network analyzer to +/-10kHz. When ordering, please specify CW or SSB, and the stub will be cut to plus 25 kHz from the sub band edge.
A single stub can be connected to the output of an amplifier with a UHF tee connector. For multi band operation, the stub(s) may be connected after the antenna switch. There is no requirement for a specific length of coax between the amplifier and the stub. Well shielded line should be used to prevent radiation of harmonics before they get to the stub. Two or more stubs for a given band may be used together. For example, a CS-4 and a CS-5 together will null 40,15 and 10. They would be connected with two UHF tee connectors close to the amplifier, if possible, to minimize pick up or radiation on the connecting lead. For stations where the amplifier is used on more than one band, automatic stub switching can be accomplished [and the] station antennas can be switched at the same time.
It is worth noting that not only has George W9VJN passed on what he has learned in his book, he is ensuring that his product knowledge & products remain available by passing the torch at INRAD. International Radio now in the very capable hands of new owners Trey, N5KO, and Mark, AG9A with George staying involved in the development of new products.
A recommended Book!