Home > HF > Advice to New Hams

Advice to New Hams

Today I was listening to some advice being given to a new ham. I applaud all ham radio operators who help a new ham, especially those who help real beginners. The advice I heard today was all good stuff, but like lots of advice I’ve heard before, it is what is ommitted that is often the problem.

Today’s advice was about dipole antennas, and there was the usual healthy discussion about resonant versus random length, about feeding with coax versus feeding with open wire etc, but during the whole discussion about feeding a dipole with coax, I only heard one person mention a balun-maybe they assumed the new ham knew he needed one to go from coax to dipole.

Given most new hams start off feeding antennas with coax, this information about a balun is vital. In this particular case, the new ham had a G5RV which was not working very well on 80m, but in my experience, with a suitable balun between coax and ladder line, the G5RV works just fine on 80m. I have no idea if the new ham’s antenna utilised a balun but it did make me wonder. I also hear the occasional recommendation to tune the antenna by adjusting the coax length- if you need to do this you have a problem, and after shortening the coax, you still have a problem regardless of indicated SWR.

Advertisements
Categories: HF
  1. Felix vk4fuq
    April 24, 2011 at 8:48 pm

    G’day David, this can be a very complex subject. In recent days I’ve actually gone back to using a simple (home brew) 4:1 voltage balun out of my T match to feed my various tuned lines on my HF antennas.

    However there are ‘some’ situations where the choke or current mode balun is the better balun. The G5RV is an example. A voltage balun will not work well placed at the junction of the coax/ balanced line interface. The 1:1 choke balun works much better in this application with its unique ability to ‘choke off’ unwanted braid currents.

    The choke or current mode balun is a unique type of balun with the quasi magical abilty to work optimally in many seemingly very different applications thanks to its ability to provide a ‘floating’ voltage output with equalised currents. Yes a potentially very complex and involved subject. Interesting though. 73 Felix vk4fuq.

  2. David
    April 24, 2011 at 9:06 pm

    Agree on the current balun comment- but as I said, a balun (whichever type) is always required when going from coax to dipole. The G5RV and the variant I use (ZS6BKW) should have as you say a 1:1 current balun at the termination of coax to open wire or ladder line. BTW the other bit of advice often given is to use an ugly balun or simple air wound coil of coax which is not effective below about 14 MHz.

  3. Felix vk4fuq
    April 24, 2011 at 11:06 pm

    There is a lot of widely varying opinion on the number of coil turns needed. Certainly for use on the lower frequencies many turns are needed to secure sufficient ‘choke’ inductance. Yet I have seen published designs in respected publications claiming good low frequency current mode balun performance with surprisingly few turns, even when using an ‘air’ former.

    I wind all my baluns on ordinary ‘radio loopstick’ ferrite rod material, which I think is superior to ferrite toroids for several reasons, and 14 turns or so provides good balun performance down to at least 3.5 MHz.

    Interestingly enough, I think voltage baluns have lower insertion loss than choke (current mode) baluns. Some time ago I had two of my home brew baluns professionally tested, one voltage and one current balun and the voltage balun had almost immeasurable insertion loss whilst the choke balun was still low, but a litle higher. Regards, Felix vk4fuq.

  4. olsenstours
    April 25, 2011 at 12:56 am

    Walter Maxwell would disagree that any number of turns on an air-former will work effectively at frequencies below 14 MHz. On a ferrite yes no problem. A rod is in fact in many ways superior to a toroid at lower frequencies due to lower potential for saturation.

  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: