Friday, September 16, 2005

A couple of new MFJ antennas

Last week I ordered a couple of new antennas from MFJ to extend the usefulness of my Yaesu VX-5RS. They arrived today, an MFJ-1730 Pocket Roll-Up J-Pole 2M, and an MFJ-1729 Power*Gain 2M/440MHz Magnet Mount Mobile. Since the mag mount antenna has a PL259 connector on the coax, I also got an 0.5M SO239-to-SMA adapter cable from Gigaparts. (PL-259 is male and connects to the female SO239 connector. My VX-5 has an SMA connector.)

The reason for getting an adapter cable rather than a PL259-to-BNC adapter, and then connecting that to my BNC-to-SMA adapter, is that doing so can unduly stress the SMA connector on the radio. Having the slack provided by a half meter of coax helps take the strain off the radio's connector. If anyone makes a direct PL259-to-SMA adapter I haven't run across it.

The first thing I did was take down the homebrew 2M J-Pole which I've been using, and hung up the MFJ-1730. It's made out of some BNC-terminated coaxial cable attached to 300 Ohm twin-lead. The solder joints and the part of the twinlead that is notched to make the reflector arm of the antenna are covered in heat shrink tubing. The top end of the twinlead has a small hole punched in it for hanging it up. I looped a cable tie through it so I have about a 2 - 3" loop for more flexibility in hanging it up.

Reception of various AM stations and the MARC 2M repeater with the MFJ-1730 J-Pole was only so-so, with a good amount of noise. There's a lot of metal fairly nearby in my office and the instruction sheet that came with the MFJ J-Pole warns that if it's too close to metal, even metal window frames, it can get detuned. I haven't transmitted with the MFJ-1730 yet. I'll wait until I can do so outside away from metal items.

The MFJ-1729 magnet mount mobile antenna gave me better results, even indoors. Magnet mount antennas need a ground plane for best operation. When stuck on top of a vehicle, the roof serves this role. If using such an antenna away from a vehicle, you can use something else, even a cookie sheet, for a ground plane. Since I was in my office I stuck it on top of my metal gun cabinet, which worked well.

Reception with the MFJ-1729 in my office was very good and although I didn't specifically request a signal report, when I checked into the Friday night MARC net, they seemed to be able to hear me well.

The same day I ordered the antenna stuff from Gigaparts and MFJ, I also ordered an external microphone and extra Lithium-Ion battery pack from Universal Radio. I still haven't received an email indicating they shipped. I'll bug them if I don't hear anything by close of business on Monday.

3 comments:

Antenna Design said...

Hey Dave!
First time reader just thought your work was really great. You have amazing work. What I mean by that is you're very detail oriented and its very good! Looking forward to read some more!
Thanks

Dave Markowitz said...

Thank you!

yeasu123 said...

Dave, just found you. I love that you are a Ham and write about other things. Very cool. I'm sure I will be a big fan.
KA6NOG 73 Steve McGuire