DX RX

The Doctor of DX prescribes the
answers to your problems, low and
high, near and far.

A how to of what for, by Mike(aka Billy)Graham, NE1V

My Dawg Ate My Radio!!

Many thanks to Barry Onigman, N1DNU, for the following hints and kinks. With Christmas coming, and as silly as some of this stuff may sound, these are questions which may be asked. This text has been edited to fit in the space I have available. The full text may be viewed at: http://tiac.net/users/barryo. Quick hints, which your salesman may have neglected to tell you ! Or, the answer to "Can you tell me, what did I do wrong?”

My rig won't power on !

Be sure that not only do you have the power plug connected, make sure the 'MOX' button (button on the radio that puts the radio into transmit mode) is NOT depressed. Most manufacturers have included a logic circuit in modern radios to inhibit powering up in the transmit mode, a sensible precaution.

I can't get full power from my SSB rig!

A 100 watt SSB radio is designed to put out 100 watts of PEP(Peak Envelope Power) in the SSB mode. If you are trying to see that in your panel or wattmeter, you are seeing an average reading, not the PEP reading.

My DAWG ate my radio!!

Well, I suppose we could wait for it to show up again. But seriously, if your radio should have an unfortunate incident with the pup's mouth, puddle, lake, pond or toilet, don't despair. Dry the radio out with gentle heat right away. The worst thing you can do to a wet radio is power it up while it's wet. If you have access to a freon bath or other circuit board cleaning operation, this is probably the best way to expel all moisture and contaminants from a radio and not affect the circuits. Cover all open tuning coils and adjustments if possible prior to the attempt. Or use pure ethanol (no mixing with fruit juice!). Isopropyl can work too if you use the Q-tip method. It’s a true labor of love to resurrect a radio from the drink: good luck! Ÿ What is the impact of SWR on HF (to 30 MHz)? My SWR is about 6:1. Is that OK? Some HF antennas can still be effective with high VSWR readings. If you have a Yagi or other tuned antenna system with high SWR, you've got some serious trouble. But wire type antennas can show a high SWR and still work OK. A dipole or inverted V fed with balanced line can show high SWR and still work: typically you'll need a balun to get the SWR in the range where a transmatch (tuner) can tune it (some have a balun built in). One major concern of high VSWR is high voltage/current points in your feed line, antenna, transmatch and power amp stage of the transmitter. Use of a tuner will help the transmitter - keep in mind that max ratings for feeds and antennas are based upon assumptions of low VSWR and the tuner will not change high voltage/ current points on the feed line or antenna. On the top band nasty high voltages can toast your transmatch if you tune a high SWR. Few transmatches can take power on 160M.

Where do I measure SWR? How do I tune an antenna?

The best place to measure SWR, if possible, is at the LOAD (antenna input). Place the meter or coupler at the feedpoint of the antenna if you can. If you are installing a new 2 meter vertical ‘ground test’ it first. A short piece of mast can make a temporary stand. Some antenna designs call for a conductive support, so watch using wood or PVC as the support. Keep the antenna as far away from any surrounding metal as you can and check for a reasonable match. Note that the lower the frequency, the more interaction there is between the ground and surrounding objects. And that can affect SWR readings.

I'm using a vertical on HF. What is the purpose of 'radials' and what is an effective counterpoise?

For those antennas advertised as 'radials required' this means that the antenna wants to 'see it's image' to be most effective. In areas where the ground conductivity is good (i.e. salt marsh) a ground mounted vertical does not need too much of a counterpoise. If you live where I do (sandy soil, dry, rocky) an extensive image must be put down, the closer the antenna is to ground the more extensive. Many people get hung up on exactly 1/4 wave or multiples on their 'radials' - this is not as critical as the total amount of counterpoise used. The basic rule is 'the more the merrier'.

I'm using a vertical that claims 'no radials required'. How??? What are the drawbacks with this style of antenna?

This type of antenna is usually based upon the 1/2 wave radiator, with a 1/4 wave 'stub', or some sort matching network at the base. This antenna should normally be kept off of the ground by at least 1/8 wave at the lowest frequency for best performance. Antennas like this will cost more and be large relative to the frequency bands covered.

I'm using a vertical antenna that is advertised as 40 through 10M coverage, but I can get it to work on 80M and 6M too. Does it hurt anything to do this?

YES. By forcing any antenna to accept power at a frequency it is not designed for you can burn out traps and matching networks very easily. An antenna rated for over 1KW can be blown out by 100 watts or less on the wrong frequency. Check with the manufacturer before transmitting through an antenna on a frequency it is not designed for. Running a KW through a G5RV antenna can be done in some instances, but the voltage/current points can exceed the ratings of the feed line or balun. If you want to be loud on the air, make or buy an antenna that is resonant on the frequency you want to operate on first. Spending money on an amplifier without doing something to help the receiving end is a losing proposition.

Should I get a tuner (transmatch)?

Two advantages of using a transmatch are that it allows you to minimize any residual VSWR seen by the radio even on a well matched antenna system, and it provides a band pass filter for both receive and transmit. Many inexpensive transmatches will have metering, dummy loads, built in 4:1 baluns and antenna switches for operating convenience. If not built into your radio, a tuner is highly recommended for any HF station. Using a tuner or transmatch does not tune antennas; it provides the transmitter with a proper match to the feedline. If you want to 'tune the antenna', use a coupler.

What does a balun do; should I get one?

The balun converts from a balanced to unbalanced condition. A dipole is normally a balanced antenna. To use it with coaxial cable, which is unbalanced, a balun is required to keep the relationship between the two proper. Baluns can incorporate a transformer also, hence the 4:1, 6:1 and other ratios. Use of a balun will tend to prevent RF currents from flowing on a feedline, and can help reduce interference when transmitting. When used with an antenna, baluns tend to keep the pattern of the antenna close to it's design.

When should I use a dummy load?

A dummy load comes in handy when trying to troubleshoot. It's a good idea to have one on hand because a lot of times it's not possible to determine what is wrong without one. It's also 'polite' (and the law) to do modulation and transmitter testing off air.

Do I use a low(high)-pass filter on HF?

Low pass filters are effective when your HF station is transmitting harmonics that interfere with radios or TV’s. The key is that if the interference is only on certain channels or frequencies: then a low-pass might help. A low pass filter with a cut-off of 30 MHz can sometimes help prevent the IF of a TV (~45MHz) from being overloaded. High pass filters work well on receivers that are getting harmonic interference from HF transmitters. These typically are placed on the VCR/TV or radio antenna cable at the point they enter the receiver's cabinet. The good news is that most ham equipment today is very clean, and low pass filters are not required to insure clean transmissions for properly running modern ham gear. The bad news is that many receivers are as 'broad as a barn door' and are not designed with much forethought to RF fields being present.

How can I reduce phone interference?

Try choking off the phone lines with a ferrite filter or two. There are neat little filters available with modular plugs that fit right into the phone jack. In severe cases, kits are available to install inside the phone case itself. Orient your antenna at right angles to the phone lines if possible, and keep antennas away from electrical lines as far as practical.

Again, thanks Barry……73 es best DX and a Very Happy Holiday to all.

73 de NE1V

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