Q: One of our members installed a new antenna on his car for 2 meters. To get to the antenna connection on the radio would involve about 4 hours work and removal of most of his dash. Can you use a field strength meter to tune the antenna?
A: From member Bart Hill: He really needs an SWR meter to validate the antenna SWR. However, if he bought a mobile antenna that is specifically for 2 meters there should be no need to check the SWR as long as he thinks the installed coax cable is adequate. This is because any quality 2 meter antenna is already tuned. If he really wants to check, and can’t easily get to the back of the installed radio then he can use another radio and another piece of coax. Just disconnect the antenna from the installed coax, connect the new coax to the antenna, SWR meter and radio. Then he can see what the antenna is doing. On my mobiles I use a Diamond antenna and have never had a problem with SWR.
Q: I bought a Nagoya NA-771 for my Baofeng. Problem is it has the male connector, so I had to buy an adapter so it would fit. Will this small SMA adapter cause me to lose gain?
A: From member Mike Cline: The short answer is yes, loss of power to the antenna. Each connection made on 2 meters will show higher loss than extra connections made on HF. The loss will be expressed as less power (watts) getting to the antenna rather than gain. Gain can only be expressed as a increase of operating signal over a known antenna. This is generally gain over a Di-pole in free space. Being as we can not see radio power, if you think about power (watts) as water in a pipe the connector will block a small amount of signal, even with a good quality connector. With a good quality connector being used I would expect a loss of about a quarter watt. This may not seam like a lot and it isn’t but when you have a marginal antenna in place and low power coming from the transmitter it all adds up. Some of the loss of signal may be regained by increasing the “gain” or efficiency of the antenna. Once the power is lost it can not be regained but the antenna can be more efficient and that may overcome the loss. I have seen many ground plain additions on to the base of the antenna show a increase in quality of signal reports from distant stations. This is done by adding a 19 inch long pigtail to the base of the “rubber duck” antenna on the handheld. Your mileage may vary.
Q: What is a duplexer, and what does it do?
A: From Wikipedia: A duplexer is an electronic device that allows bi-directional (duplex) communication over a single path. In radar and radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer.