Before you jump on a set of those $83 or so VHF duplexers…
If you are shopping for VHF duplexers for a repeater, we want to caution you that there is one brand being sold on a very popular website which the seller has opted to
stop including one very critical piece of information about. An excellent, recent example of this is the Fumei SGQ-450A VHF mobile/compact style duplexer, as seen in this photo. What the seller has stopped mentioning in their multiple listings for this item on at least one market website is the fact these duplexers will not operate at a split of less than 5 MHz. The seller DotDotTech on Amazon had previously included a mention of this detail in poorly worded, in broken English, but has since begun to omit that specification in their listing(s). It appears the seller is actually located outside the U.S. and there have been multiple mentions and comments by Amateur Radio operators that they had purchased these — only to discover they could not be tuned to a 600 KHz split — but they were unable to establish any contact with the seller.
Whether the fact they stopped including the minimum 5 MHz required high/low split information inadvertently or intentionally is unknown. All we know is that many people have wasted their money, time, and effort by purchasing these duplexers assuming they would work at the typical ham repeater splits. These “Fumei” duplexers and this seller are not the only culprits.
This is actually a widespread problem
There are numerous other VHF mobile/compact duplexers with various brand names and model numbers being similarly marketed and sold with that same information omitted on multiple online shopping sites.
Just an FYI: the narrowest usable frequency split we know of for VHF mobile/compact duplexers is 3 MHz, and a set of those goes for around $600 (usually more). Bottom line: mobile/compact VHF duplexers will not work for 600 KHz splits — it all boils down to the laws of physics, which are pretty much immutable.
Note: We are posting this article for educational and informational purposes, and any mention of brands, retailers, websites, etc. is therefore used under “Fair Use” guidelines.
