Diamond dual band mobile antenna evaluation-Notes, by Karl Shoemaker, AK2O
Model # NR-72BNMO
This antenna was purchased a few years ago and installed on my SUV. Operation appeared to be normal as expected by a compromise very small antenna for two bands. For some reason the return loss was not checked on VHF since my attention was on the 70-cm band at the time. Recently a performance check found the return loss was very good on UHF however, very bad on VHF; 20 db and 5 db respectively.
In further checking on-line information one retailer stated in the description "Will not work center mounted on the roof" (proper casing corrected). Either the Author missed that warning or it was added later on the web site. Either way is a problem since the antenna was center mounted on the roof like most installs. Therefore, if you are purchasing one of these take into account you may want to reserve the mount location on the fender or other "edge" area of your vehicle. Otherwise, it's a well built antenna and does duplex well. Having said that there will always be some energy on the UHF band from the VHF transmitter from simple math of the third harmonic; there's no way to get completely away from that unless you want to use a "real" duplexer to filter that out. (not the cheap "duplexer" you may buy at the "ham" stores).
The defective antenna was replaced with a Comet B-10. The two band sweeps were performed with 14 and 23 db return loss on VHF and UHF respectively. This will work however, the Author continues to research a dual-band antenna with better RL design over the current ones found on the market.
Conclusions: Pay attention to the description of any product prior to purchasing.