Sunday, February 14, 2021

A Ham Radio Series 21 - A Little Getting Started on HF Information

Most of the getting started information that I see is based on VHF radios, like the ubiquitous Baofeng VHF HTs (Handie Talkies).  There's nothing wrong with that, but since I've been more interested in High Frequency bands (HF - also known as shortwave), I see a few things that should get some mention. 

There are currently nine bands in the HF spectrum from 3 to 30 MHz.  These are referred to by wavelength, a tradition that's a bit odd when you realize the wavelength the bands are named for appears in exactly one of the bands. 
  • 80 m: 3.50 to 4.00  MHz (80m itself is 3.75 MHz)
  • 60 m: five assigned channels at 5.332 to 5.405 MHz (60 m is 5.00 MHz)
  • 40 m: 7.00 to 7.30  MHz (40m is 7.50 MHz)
  • 30 m: 10.10 to 10.15 MHz (CW & data only) (30m is 10.00 MHz)
  • 20 m: 14.00  14.35 MHz (20m is 15.00MHz
  • 17 m: 18.068 to 18.168 MHz (17m is 17.647 MHz)
  • 15 m: 21.00 to 21.45 MHz (15m is 20 MHz)
  • 12 m: 24.89 to 24.99 MHz (12m is 25 MHz)
  • 10 m: 28.00 to 29.70 MHz (10m is 30 MHz)
As we've pointed out in some of the various antenna posts over the years, antennas work best when they're cut to a specific length for the desired frequency, called being resonant.  The only useful thing about referring to the bands by wavelength is it gives you some feel for how big those antennas should be.  (A half wave antenna for 40 meters is 20 meters long).  For statesiders, you only need to remember one of the following two equations.  A quarter wave wire, in feet is given by L = 234/freq (where frequency is in MHz) while a half wave is twice that or L = 468/freq.  That number is already compensated for the "end effect" of cutting off the wire and wrapping a little into a loop to mount the antenna.  It's about 5% shorter than the wavelength in free space.

You can get one of these charts in many places.  Keep one near your radio.  I do. 

I can tell you based on years of operating all those bands that they all have distinctive behaviors and distinctive groups that hang out on them all the time.  How do you choose which one you might want to start operating on?  There are websites (like this one) that give you an overview of what to expect on each band, and you can listen around  Do you need a separate antenna for each band?  Do you need to run separate cables from each antenna into your station? 

You don't have to have a separate antenna for every band, but it's not that hard to get an acceptable signal on all of those bands with one antenna, like a multiband vertical.  Perhaps you might put up a wire for one or all of the lower bands (80, 40 or 30m) and a triband antenna for 20,15 and 10m - most of the spectrum on just two antennas.

For many years in this house, my low band antenna was an Off Center Fed Dipole, OCFD, cut for 40m.  OCFD means the dipole was a normal half wave long (468/7.1 or 65.9 feet total length), but instead of the coax being attached at the middle, about 33 feet from each end, I attached the coax at about half of that from one end or 16.5' from one and left the other end 49.4' long.  That changed the antenna so that one side was 1/8 wave long and the other 3/8 wave long.  Because of that asymmetry, a balun (balanced to unbalanced transformer) isn't needed, however something I read convinced me to use a transformer to 450 ohms at the feedpoint (that's 9:1 impedance or 3:1 turns ratios).  A 3:1 restricted range antenna tuner, like the big radio companies tend to put in their radios, tuned it on every band from 40 to 6m. 

There's almost an unlimited number of ways to solve the antenna problem.  A fan array is an easy antenna to make: it's a group of dipoles cut to frequency and tied together at one feed point.  The wires are kept spaced apart with plastic insulators, and since the impedances of the off band antennas are so wrong for the transmit signal, they don't interact.  For example, if you're on 20m the 80, 40 and 10m dipoles don't absorb much power because they're very wrong impedances.  

The hidden bonus here is that half wave antennas resonate on odd harmonics.  That adds coverage on 15m as the third harmonic of 40m, (that is, frequencies in the 40 band multiplied by 3 are in the 15 meter band) so although you see four wires, it's a five band antenna.  Yes, I've used one of these, a bit over 35 years ago.  It worked fine. 

Another standard antenna is an end-fed wire.  These are called Zepp antennas because it was the type used when Zeppelins were the aircraft of the day.  End fed half waves are high impedance, but friends tell me their end-fed wires work fine with an antenna tuner.  Antenna tuners were covered early in this series, more of a "how they work" than things to care about or watch out for. 

The major thing to watch out for when using an antenna tuner anywhere in your system is that the best place for the tuner is at the antenna feed point.  That tends to be really inconvenient, and the most convenient place is in the shack.  The price you pay for that convenience is more loss in the transmission lines as the signal bounces back and forth due to the mismatch.  Which says if you're going to scrimp anywhere, the coax might not be the place.  The loss in a piece of coax is a stronger function of diameter than the dielectric (insulators) used, so RG-8 or RG-213 is better than the smaller RG-58.  Which matters more for long cable runs than short pieces of cable.


  1. I will be watching this series closely, as I have been a ham since about 1972, but I have not been active on HF for many years. Any advice you can give as far as inexpensive rigs, decent CW, QRP rigs, etc, would be great. I am not too familiar with the use of computers and ham radio, but I am somewhat aware of the positive aspects of them. I look forward to the advice and information you can put forth.
    As a 12 year old novice way back when, with Xtal controlled the only option, things now make the old way we did things seem ancient, even almost like spark gap radio or something, compared with the brilliant people in ham radio now.


    1. I was first licensed in 1976 and have had one continuously since then. How active I am has varied, and I've made contacts on every band from 160 to 1.2 GHz (except 60m) but I've always come back to HF. My first station was a Heathkit HW-16 and HG-10B VFO because that was right after they dropped the rule that novices had to use crystals.

      This is the 21st post in the Ham Radio Series. I've also done other posts on radio, antennas and other electronic topics. In the right column, right under the lists of blogs, there's a section on Special Pages which link Radio Sunday, this series and some more.

      At the top of the page, on the left is a little white box with a magnifying glass icon in it and the Blogger "B" logo next to it. That's a search engine set to search my blog. With just about 11 years of writing this, I use that All The Time to try to find something I remember posting. You can enter a word to search on and if the word isn't too common, get a page of results to go through.

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  3. Good post, SiG! Lots of solid, basic info. I was finally able to get my FT-1000D to load into my 88' end-fed. I had to get the ends up to 20', and the center up to 30'. Now I can use it on 75 through 20, and the internal tuner can find a match.

  4. Good article! I had a 160 meter OCFD about 12 years ago. It was a real "worm-burner" because it was at best 20' above the ground. But I could hear a lot and I think I made 1, and only 1, contact on 160 SSB with it. I could get out on 17 meters fairly well. My last place I had some kind of generally non-resonant OCFD. I fed it 1/4 wavelength on 20 from the end at the shack. My first contact on 20 was with a big-gun station 400 miles east of Moscow, Russia.

    I have been thinking about putting up a fan dipole as you describe using my 40 meter dipole as the longest element but when I modeled it in 4nec2 it was really "ugly" on 10 meters. I got this hunch and put the 10 meter dipole above the 40 meter dipole. The results were much better. I do have an idea how to physically execute this so the 10 meter dipole stays above the others.

    Just as I was about finished with this reply, we got another power blackout here in South Central Texas. The winter storm that hit us has the Electric Reliability Council of Texas mandating these rolling blackouts. I posted this as soon as I could get power for Internet.

    1. Hope you get some electricity back.

      I have a handful of contacts on 160, using either my 40m OCFD or my 80/40 vertical. In both cases there was circuitry in the shack to extend the matching.

      I've never found 160 that interesting though. Not sure why, beside being very noisy.

  5. I'll issue a warning about the fan dipole, and it applies to any other multi-band antenna-tuning is a bear. I built a DX Commander last year, and it took 3 days to get it tuned as well as it could be tuned. Once it was tuned, it's been a great antenna.