So far the first five episodes of the Ham Radio Q and A show have generated quite a bit of interest and response. They’ve also spurred more than a few questions, so I thought I’d take a moment and follow up on a few of the questions asked.
In the episode titled RF Chokes and Baluns, I talk about why it may be necessary to add an RF choke to your antenna’s feed line. Youtube user Julio asks: My questions is about 1:1 & 4:1 BALUN. When am I suposed to use one or the other?
Well, 1:1 and 4:1 are ratios of impedance. Normal impedance for amateur radio equipment is 50 Ohms, so a 1:1 balun will convert a 50 Ohm balanced antenna to 50 Ohm unbalanced feedline. Best example would be converting a 1/2 wave dipole antenna (which actually is 70 Ohms, but close enough for this illustration) to 50 ohm coaxial cable.
A 4:1 balun will convert a 200 Ohm impedance down to 50 Ohms. Some examples of antennas that could have 200 Ohms of impedance at their feedpoint include HF verticals or off-center fed dipoles (like Windom Antennas). If you are planning to feed these antennas with coax, you will most likely need a 4:1 balun to match the impedance at the feedpoint.
A commercially built antenna will most likely tell you if you need a 1:1 or 4:1 balun. If you are building an antenna, using an antenna analyzer like the MFJ-269 will tell you what the impedance is at the feedpoint, which will then indicate what type of balun is needed.
My go-to source for information on baluns is usually the ARRL Handbook. But that information can be very technical and the book, unfortunately, is densely written. I’ll add homebrewing 1:1 and 4:1 baluns to my list of topics for a future video.
In using RF chokes. Youtube user Candi Klover writes: Can I do this for 2 meters? I get a slight amount of noise from the tv.
Yes you can. Televisions are a generator of Radio Frequency energy and their power cables can act as an antenna, causing RF Interference to affect nearby receivers, like you 2 meter rig. The best solution is to add one or more snap-on ferrite beads near where the power cord connects to the tv set. Depending on the level of interference, one may be enough, but you may need to add two or more if the RFI is particularly strong.
In the Video: RF Grounding and Ground Planes I talk about why some antennas require a ground plane and other get by without it. This generated many questions on can your house’s electrical system be also used as an RF ground point. I’ve seen published information go both ways on this topic. Some people recommend using your electrical ground as an RF ground as it will help prevent ground loops, but other articles recommend using a separate ground point for RF energy.
My recommendation is to use a second ground point. The reason being, is that unless your house has a modern, up to code electrical system, your electrical ground wire may or may not actually make it to an earth ground point. Old houses can have a mismash of electrical circuits that have been updated and modified through the years. and there may be no guarantee that the green wire in that electrical circuit truly runs to ground. Putting in a ground point for RF eliminates that problem.
Finally the video: Selecting Coax Cable generated a few question on if 75 Ohm cable like RG-6 or RG-11 can be used for amateur radio purposes. The short answer is yes it can. But there are a few caveats involved and on my website I have a blog article that talks about how to use 75 Ohm coaxial cable with your 50 Ohm antenna and transceiver. Click on the link to read the full article.
Get your questions answered!
I’m always looking for content for new shows. Do you have an amateur radio related question about antennas, equipment, or operating practices? email me via the contact form or leave a comment below and it may be featured on an upcoming episode of ham radio Q&A. Even if your question doesn’t get featured in an upcoming show, I do strive to respond to every message I receive.
Thanks for watching.