Ed Fong GMRS/MURS Antenna -DBJ-1 Commercial (pvc pipe not included)(green tag)
|
Description
DBJ-1 Published in - QST February 2003
Our most popular antenna is the DBJ-1 which is a VHF/UHF Dual Band Base Station Antenna. Commercial (152-157 MHz and (460-470 MHz). MURS/GMRS Maximum power input 75 watts. Here are the basic specs: Overall Length: 5 feet, 50 ohm feed impedance, no ground radials. Antenna feedpoint is 10 inches above the connector. U clamps, hose clamps, etc. can be used for mounting up to the first 10 inches of the antenna without affecting performance. Antenna offers “true” ½ wavelength radiator at both VHF and UHF. VHF MURS (152 -157 MHz) commercial model Configuration: 1/2 wave radiating element Maximum power: 75 watts SWR: less than 1.5 to 1 over a 3 MHz bandwidth and less than 1.7 :1 over 4 MHz bandwidth. Gain: 2.1 dBi Impedance: 50 ohms UHF GMRS (460-470 MHz) commercial model Configuration: 1/2 wave radiating element Maximum power: 75 watts SWR: less than 1.3 to 1 over a 6 MHz bandwidth and less than 1.5 :1 over 10 MHz bandwidth. Gain: 2.1 dBi (6db gain over a 2 meter J pole used at 450 MHz) Impedance: 50 ohms The published papers on these antennas are attached. Building these antennas are difficult because of the scarce availability of materials. Twinlead has long been obsoleted. All of our twinleads are special ordered from JSC wiring. It is 300 ohm open air ladder line design for transmitting. Also the ability to measure velocity factor is difficult and is absolutely necessary for this antenna to operate effectively. One can use 450 ohm open ladder line but it will not fit into a 3/4 inch 200 psi pvc pipe and is also too wide spacing for UHF. Thus we make this design available to the general public at reasonable cost. Don’t be fool by claims of dual band performance. Although traditional VHF J-pole antennas will resonate at UHF, they suffer a –6dB loss at UHF over a ¼ wavelength groundplane. We see many claims of dual band performance sold on the internet but when we purchased many of these antennas they are just VHF antennas that also resonate at UHF. At UHF most of these imitations have horizontal loss of -6dB. Examples of these are "copper J-poles", "slim jim", "arrow". I first introduced the concept of this antenna in Feb. 2003 QST. It is the same antenna that appears on the front cover of the ARRL VHF/UHF Antenna Classics Handbook. It also won the best paper of the month award. It offers true ½ wavelength performance at both VHF and UHF with no ground radials. SWR is less than 1.3 to 1 on both bands. The antenna has been so successful that it has been adopted by the Red Cross, ARES and numerous municipalities for emergency deployment. Copies of these agencies evaluation reports are available by emailing me. A good benchmark is if an antenna configuration does not appear in a ARRL publication, it probably does not work as claimed. This antenna is complete with exception of the 5 feet of ¾ inch Class 200 PVC pipe needed for the antenna. Just insert it into the PVC pipe and you are ready to go. PVC PIPE NOT INCLUDED!
REQUIRES 5ft of 3/4 inch thinwall pipe (available at Lowes) Green Tag
|
You may also like
More from Ed Fong
More from Communications
Recently viewed