Reviewed by Pascal Villeneuve, VA2PV
In the past few years, VHF/UHF digital voice communication has been one of the fastest growing segments of Amateur Radio. D-STAR and System Fusion (C4FM) were specifically designed for Amateur Radio, but this is not the case with DMR — Digital Mobile Radio. It is an open standard, developed by the European Telecommunications Standards Institute (ETSI). As such, this technology is available to any company willing to build a digital radio, such as the BridgeCom Systems D-500 (by TEKK) reviewed this month. Introduction to DMR There are three types of DMR — Tier I, Tier II, and Tier III. To learn more about DMR, I strongly suggest that you read “Introduction to Digital Mobile Radio (DMR)” by John S. Burningham, W2XAB, in the October 2015 issue of QST. In this review, we will concentrate on the widespread Tier II DMR network. You will need to understand a bit about this technology to program your DMR radio. As DMR was not developed specifically for Amateur Radio, the terms are different from what we are used to. Tier II DMR uses TDMA (Time Division Multiple Access), which is a frequency-sharing protocol. You can have two conversations on the same frequency without interfering with each other. This is very efficient, as Tier II TDMA uses a 12.5 kHz bandwidth with two time slots. The switching is very fast, thus allowing for two simultaneous contacts on the same frequency, using this time-sharing method.
Reviewed by Rick Palm, K1CE
QST Contributing Editor
Using BridgeCom Systems’ new 222 MHz (1.25 meter band) mobile radio was a walk down memory lane for me. In the late ’70s and early ’80s, I was part of a small, quirky but devoted group who ragchewed on two 220 MHz repeaters in northern Connecticut and western Massachusetts. One machine was on Talcott Mountain overlooking Hartford, and was run by the son of a major city developer. The other was owned/ controlled by my longtime friend, Paul Koplow, WA1VEI, on Mt Lincoln in the Berkshires. Our radios back then were quirky, too: mine was a Midland (crystalcontrolled, no PLL) that looked like a battered, old CB radio from a trucker’s cab — the kind you might find today in a pawn shop. Later I had a Yaesu Memorizer for the band, which was a great radio. We rolled our eyes and suffered one user who used the autopatch to talk with his wife on his commute home every evening with over-the-top kissing and cooing sounds. Off-air and even on-the-air counseling sailed over his head.
Nowadays, the 222 – 225 MHz band is still a great spot for repeaters and their disciples. I had a lot of fun getting back on this band thanks to the BridgeCom BCM-220. Continuing with the nostalgic theme here, the company, which is based in Smithville, Missouri, evokes the feel and quality of those old radios in their new products, especially this one. The BCM-220 is built like a tank, with commercial-grade construction, and a high-quality, heavy-duty mic that eschews the numerous functions/ buttons that populate some mics. The BCM-220’s mic has a simple DTMF keypad and only three function buttons below it: the first to switch between memory and VFO modes, and the second and third buttons for frequency or channel up and down. That’s it — and I love it! It’s heavy and feels good in my mic hand. Indeed, all of the radio’s functionality seems to be focused on the essentials, and that’s a plus in my book.
International Crystal Manufacturing (ICM) of Oklahoma City has announced that it will be going out of business, probably at the end of May. Royden Freeland Jr., W5EMH, son of the company’s founder, posted a letter this week on the ICM website.
“We will be honoring all orders that we have already taken and will be able to fill a limited amount of new orders dependent upon raw materials available,” Freeland said. “We would like to thank you for your past business. The success of ICM over the previous 66 years has been largely due to its amazing customer base.”
International Crystal produces RF control devices — quartz crystals, oscillators, QCM crystals, filters, TCXOs/VCTCXOs, and precision crystals.
Jason comes by the booth with Gary Pearce from HamRadioNow for a chat, minute 18:30. Watch and enjoy!
Receiver desense testing by Karl Shoemaker, AK2O
Due to the inability of certain people to communicate properly and understand all the aspects of site testing this page was created to read, compare notes and build on for the benefit of all. Human communication, comprehension and understanding problems is beyond the scope of this document, however the reader should keep these problems in mind when dealing with site issues and interfacing with other companies and government Agencies. Misunderstandings, bogus readings, log entries, technician and management diagnostics and plan of actions for problem solving are commonly mis-directed with considerable time and expense wasted in the wrong direction of efforts. This can lead to the general desensitation (pun intended) and poor attitude of the workforce in most any private company or government in the technical (repair) field around this country. Fortunately, there still is a handful of technicians that care to understand what the problem is and the proper way to solve, or at least, reduce the symptoms to an acceptable figure. If you are reading this it's most like you are in one of the latter. This is a good thing.