HT Antenna Improvement

The handheld transceiver (HT) is likely a new ham’s first radio.  This VHF/UHF rig is relatively inexpensive, compact and fairly useful for local communication via repeater or simplex operation.

Unfortunately, HT  performance is typically limited by its low power and cheap factory antenna.

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There are three easy ways to improve the HT antenna.  These ideas are from our post on Understanding Antennas but we wanted to elaborate a bit on them here.

The first improvement is to get a 2m ¼-wave or 5/8-wave whip antenna.

This 2m ¼-wave whip is much longer (~19″) compared to the factory antenna but gives dramatically better performance (roughly equivalent of 5x power):

QW whip

This telescoping 5/8-wave whip should (in theory) perform better than the ¼-wave monopole (shown with 5/8-wave mobile whip):

5_8 Whip

These two antennas can be purchased new in the $20-30 range; well worth the money.

While the antenna can be improved with a longer whip, vertical monopole performance is also limited by the HT’s indirect ground plane.

The counterpoise that makes the vertical monopole behave like a λ/2 dipole on a HT is the operator’s body.  It is capacitively coupled to the ham’s body through the plastic case and metal shell around the RF circuitry.

This indirect counterpoise coupling is not only weak but also highly variable and unpredictable.

The good news is that we can improve the counterpoise simply by adding a wire to the HT antenna connection.

By connecting a ¼-wave  wire (~19” for 146MHz) to the antenna connector outer terminal, we create a physical counterpoise in place of the indirect ground plane through the operator’s body.

This gives superior performance under difficult conditions and is easy to do.

These physical counterpoise wires are known as rat tails or tiger tails due to their appearance.

Rat tail counterpoise installation is quick and easy.  Simply unscrew the antenna, slip the rat tail over the connector and re-attach the antenna

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The rat tail can simply hang down in a gentle arc where it won’t be much in the way of anything. Even better, you can hold the wire out  in the direction of communication.  Gain/directivity is achieved Continue reading

Indirect RF Hazards

Part 3 on Safety

Safety is an important topic in ham radio.  There are 11 questions on electrical hazards in the USA Technician class license exam pool, 13 questions on tower safety and associated grounding, and 13 questions on radio frequency (RF) hazards.

Part 1 on general electrical hazards and Part 2 on contact RF hazards were posted previously.  This post will address indirect RF hazards.  In case you are not familiar with the specifics of RF energy, refer to our post on the subject.

Here we are concerned about non-contact RF energy.  A long and involved topic (sorry about that) but full of useful detail.

While it involves radiation, RF energy radiates at lower wavelengths where it is least hazardous.

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From the electromagnetic spectrum diagram above we see that radio waves are on the low end of energy levels.  As the frequency increases (wavelengths decrease) the energy in electron volts increases exponentially.  Energy above 250eV (or so) is ionizing, which in addition to radiation burns can cause cell damage and mutations, leading to cancer and other maladies, as would radioactive material.

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Fortunately for hams, all radio frequencies are well below the ionizing radiation energy levels.

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Ham radio operators are radio  active, not radioactive. 🙂Amateur radio activeNow just because RF radiation is non-ionizing doesn’t mean it is completely safe.  Besides the direct contact hazard, exposure to radio frequency energy may cause localized tissue heating, particularly in the eyes and male reproductive area (here’s where a lady ham has an advantage, hihi).  Non-thermal effects of RF radiation are being studied constantly because, while compelling, they are somewhat ambiguous and unproven.

Because RF energy has this radiated exposure risk, rules and regulations have arisen to protect people from such hazards.  In the USA this is done at the federal level by both the FCC (radio communications) and OSHA (occupational).  There are also guidelines for RF radiation published by the ARRL and the IEEE.  Internationally, most countries apart from the US have similar guidelines, as does the World Health Organization (WHO).  References to some of these are given at the end of this presentation.

Specific to US radio amateurs, the FCC instituted RF field exposure limits called Maximum Permissible Exposure (MPE). Continue reading

Radio Frequency (RF)

Radio signals are sent via radio waves, which are a form of electromagnetic energy or radiation. T3A07-2018

Recall that a radio wave consists of both electric and magnetic fields oscillating at right angles to each other.EM Fields.png

 

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Combining electrical and magnetic gives us the term electromagnetic.

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Like all waves, radio waves vibrate or oscillate at a specific rate or frequency.

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ewaves.gifThis vibration frequency is normally measured in cycles per second and its units are Hertz.  T5C05-2018.pngRates of oscillation in radio work are thousands and millions of Hertz (Hz).  With standardized metric prefixes for SI units , this means practical radio frequencies are in kHz, MHz, and GHz.

The common and familiar term RF is short for radio frequency.  It’s really an adjective, not a noun.  While we may say just RF (“You have a big RF leak, there, Fred”), we really mean radio frequency energy or signals.  RF is not a thing in and of itself.

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So what is a radio frequency , then?  They are a large chunk of frequencies in the middle of the electromagnetic spectrum (the range of possible frequencies from 0 to measurably high).  Technically radio frequencies start at low audio frequencies and run up to just below infrared light, basically 30Hz-300GHz.  Different sources specify other upper/lower boundaries because a more practical range is the low frequency band up through microwaves.  However you define it, this range of frequencies is  known as the radio spectrum.

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While hams can use very low frequencies on one end and go up to microwave frequencies at the high end, the more common radio amateur frequencies are in the shortwave, VHF, and UHF range.

We will follow up with detailed posts on the important topics of RF wavelength and amateur radio bands, along with RF safety.  Coming soon to Newhams.info; stay tuned.

 

How Far Can I Communicate?

One of the more interesting questions a new or prospective ham will have is, “how far can I communicate?”  The frustrating answer is, “it depends…” (don’t you hate hearing that?)

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There are many factors involved in the limits to distance of radio communication.  Carrier frequency is the huge one, followed by operating mode, antenna characteristics and transmit power. Time of day, solar activity and the season (spring, summer, autumn, winter) also have a big impact on range.  Natural (thunderstorms, aurora, geologic, cosmic) and man-made (crowded band, power lines, noisy electronics) interference can also limit or disrupt a radio contact.  Also factor in the use of repeaters (terrestrial and space satellites) or reflective objects (structures, moon, meteor showers), plus unusual weather conditions and you have a lot to consider.

Since many hams get started using VHF/UHF radios for local communication, let’s talk about this first.  VHF/UHF radio wave propagation is normally limited to line-of-sight, meaning the antennas at each end must have a clear path between them (no obstructions such as buildings, trees, and particularly, the earth).

3-20 miles is a realistic range for VHF/UHF hand-held radios on the ground, depending mainly on a clear path and relative height of the two parties.  Throw in a repeater with a high antenna and that range extends considerably.  Raising your own antenna up higher Continue reading

Don’t Settle for Just a HT

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Often a new ham’s first radio is a handheld transceiver (HT).  A HT represents the lowest-cost entry point to amateur radio and is relatively easy to set up and use.  Your first on-air experience as a licensed ham may involve a HT on a local VHF/UHF repeater, and that’s fine.

But don’t settle for just a HT as supplied by the manufacturer for your early ham radio experience.  You are almost certainly going to be frustrated and disappointed at its performance to the point of giving up on ham radio and wondering why all these hams are so enthusiastic about the hobby.

Don Keith N4KC makes this point eloquently  in his ‘HT Trap’ article where he discusses how easily a new ham can get discouraged with amateur radio because of the limitations of a stock HT.  I have observed this as well while helping new hams get set up in a local EmComm organization.

Huge improvements in HT performance or ease of use can be accomplished with three accessories.


First and foremost is the Continue reading