Four Metres is Dead! by Dave G3VZE

I some times hear people saying, “four metres is dead” or, “there’s nobody on four”, or, after calling CQ asking “Isn’t there anybody out there?”

Well I’ve got news for you; there probably is somebody out there calling you back, and you just don’t hear them. I know this because often, it’s me.

I reply to calling stations coming in at good strength, and get no response, despite my 60W into a 6 element beam at 50ft AGL.

My experience of four metres is that about 50% of stations are deaf; their ability to send a good signal out to the horizon is not matched by there ability to hear incoming signals over similar distances. It is usually a waste of time calling a station that is less than signal strength nine because they just will not hear me.

If you believe that four metres is dead, here are a few suggestions that may bring it back to life:-

• If you are using an unmodified FT-847 on four, then your receiver is almost certainly deaf! This can easily be overcome by using a preamp at the masthead or even on the bench. The 20dB or so of gain from preamps such as the “Spectrum communications” unit will transform your FT-847. Previously inaudible signals will pop up out of the noise and become workable.

• On some ex PMR rigs, closing down the squelch also desensitises the receiver! In other words, the further you screw the squelch round, the deafer the receiver becomes. So when you ask if the frequency is in use, or call CQ, please turn the squelch right off to be sure of hearing anyone replying to you.

• Perhaps you are using a loft antenna, or a low antenna located near the house, both are likely to cause your station to be deaf. Most houses are electrically noisy. Everything with a computer chip in it is likely to generate unwanted noise; flat screen VDUs, TVs, and low energy lighting all contribute their share. This lot combined, raises the noise floor of your receiver to the point where only strong signal will be heard. You will be totally unaware of any signals below this noise floor. Getting an antenna away from houses will considerably reduce this interference, as will increasing the height. An added bonus of increasing the height is that the strength of your transmitted signals will increase, especially if you can get the antenna above the height of the rooftops!

• Another source of noise is “braid current” that is, current flowing on the outer surface of the coaxial cable. When transmitting, braid current may flow on the outside of your coax and feed RF into any nearby conductors such as house wiring, and telephone wires. This will increase the risk of EMC problems. A similar thing will work in reverse when receiving signals. Noise from any wiring near the coax will feed into the rig via the coax braiding. The coax itself becoming a low, inefficient, and noisy antenna. Remember any power radiated from the coax is not radiated from the antenna. The answer is to use a balun when feeding a dipole, and even if you are using a “J” pole or a ground plane, a few turns of coax through a ferrite ring will provide insurance against stray braid current. Elimination of this braid current will remove this source of noise and increase the strength of your transmitted signals.

• One final point, if your antenna is horizontal, do not expect to hear much from stations using vertical antennas, because you won’t, (unless your coax is carrying braid current!) Most 4m communication is by a direct wave, and you would expect a signal to arrive at the receiving antenna with the same polarity it had when leaving the transmitting antenna. Only a very tiny part of a crossed polarised signal will be received, and this depends on the thickness of the antenna element/s, and whether there are power lines or other conductors in the path of the signal. These lines will often have vertical wires connected to horizontal wires which can absorb signals of one polarity, and re-radiate with another. If you want to work people outside your own village, your antenna must have the same polarity as the other guy’s.

You may think that you would be aware of the poor signal to noise ratio of your station, but this is unlikely for two reasons;-

1. If you are using an ex PMR rig, you do not have that most valuable of indicators, an “S” meter.

2. Because of the nature of FM reception, a receiver with a high noise level sounds very much like a receiver with a low noise level.

So if you would like to have more contacts on 4metres, consider spending a little time improving your station.

Dave, G3VZE.