Re: newbee here...just made the order...antenna question on old G5RV

Jerry Gaffke

You wanted wise ones, but I'll jump in till one shows up.

The uBitx will want to see 50 ohms, ideally under a 2 to 1 SWR, though I suspect it will
survive most anything if you power the IRF510's from not much beyond 12v.

The G5RV antenna is not resonant, the impedance it presents will be all over the map.
You really need a tuner between it and the 50 ohm coax to the uBitx.

That ZM-2 might be sufficient, I don't really know.

The fact that you cannot adjust inductance is not a plus in my book, that could be getting 
inefficient as frequencies go up and capacitive coupling between windings gets out of hand.
It claims to be good to 15 Watts, though does not really say under what conditions that might be true.
Max power it can handle will vary considerably with operating frequency and antenna impedance.

I'm happy enough with my MFJ-949E tuner/swr/dummyload
Build quality varies on the MFJ stuff, you want to lift the lid when you get it and check the solder job.

If you want to build your own tuner, you need an SWR indicator such as Diz's Tandem Match SWR indicator:
Generally the tuner itself can be a couple tuning caps from some old tube type broadcast receiver
and a hand wound inductor with an alligator clip to tap into it somewhere, check the various handbooks on that.

For the price of the 7300, you can have a half dozen uBitx's go up in flames
and try out several MFJ tuners plus some homemade ones. 
And learn an awful lot in the process.

Jerry, KE7ER

On Sun, Jul 1, 2018 at 12:32 pm, Don - KM4UDX wrote:

Finally, after a year or more of hand ringing and second guessing myself, I finally pulled the switch and ordered my uBITX! 


Believe it or not, it came down to the ICOM7300 or the uBITX.  I picked the uBITX because I love to solder and build, and when things are hard, they are much more satisfying when you finally get over the hill.  And what I learn with the uBITX will apply to any more complex and capable transceiver downstream. So I pulled the plug.  Should start the build in a few weeks. Also ordered the normal white plastic case from BG, and bnc to SO239 connectors, etc.


Questions to the wise ones: Can I hook up the uBITX my G5RV? I have a length of coax (which has a simple choke) that connects to the twinlead, which then goes to the dipole aerial WITHOUT an antenna tuner?


I borrowed 100W transceiver, and the G5RV worked just fine. But the 100W rig had an internal antenna turner, which I’m told the G5RV needs.  The uBITX does not have a antenna tuner…will it work well enough directly connected with the G5RV?


If I have to get an antenna tuner…(rats!), then I’m thinking of the ZM-2 or the like.


Guidance please!


Thank you o wise ones!




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