[webmaster note: The following are a few snippets from the article at http://www.cvarc.org/tech/crossband.html which was brought to my attention by Don, AAØBZ. I urge you to read the entire article. Thanks, Don!]

“Cross band repeating is a relatively inexpensive means for extending the range of handheld radios. The purpose of a cross band repeater is the same as any radio repeater. It allows stations to communicate that ordinarily would not be able to do so because of the distance or terrain between them.”

“A cross band repeater is similar in function to a standard repeater in that it contains a receiver and a transmitter that are linked together, but which operate on different frequencies. Voice signals that the repeater receives on its input frequency are automatically retransmitted on its output frequency. A repeater is a relay station.

A cross band repeater is implemented using a dual band 2 meter - 70 cm radio. The repeater receives signals on one amateur radio band (for example 70 cm) and retransmits those signals on a second amateur band (2 meters). Thus the name cross band repeater."

“Cross band repeating works best in simplex networks. Cross band repeating can be using (sic) on a standard repeater network, ... however, if this is done, more discipline is required by those operating on the net. The problem is that the cross band repeater will not switch into the 70 cm receive mode until after the carrier of the main 2 meter repeater has dropped. This makes the turn around times on the net (the time between the last person speaking and the next person beginning) abnormally long. If people on the main 2 meter net begin talking before the repeater carrier has dropped, the people with 70 cm handheld radios will rarely get a chance to speak. To provide for fairness on the net, anyone wishing to speak must wait until the repeater carrier has dropped before beginning to talk."

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"STANDING WAVES"
by Pete, NEØT

We are familiar with waves.  We see them in water.  Drop a stone in and a wave travels outward from the spot.  This is called a "traveling wave".  If another wave in the water travels back toward the spot, the two waves will add to set up what's called a Standing Wave.  You can generate standing waves in a styrene coffee cup by dragging it across a surface which causes it to vibrate.  The vibrating wave travels out to the cup and reflects back on itself causing a perfect standing wave, one which stands still as concentric circles in the coffee cup.  I can show you this at a meeting using the coffee Padre brews there.

The radio waves on our coax or twin-lead feed lines begin as traveling waves going from the transmitter up the line to the antenna.  If the antenna has a perfect 50 ohm radiation resistance there will be no reflection from the antenna back to the transmitter and the wave will remain traveling and only in the forward direction.  The antenna's radiation resistance is exactly equal to the feed line's "characteristic impedance" and the system looks exactly as if the feed line is infinitely long, there's nothing to reflect from.  However, if the antenna has a radiation resistance different from the 50 ohm radiation resistance there will be a fraction of the forward wave that reflects back toward the transmitter.  The result is the sum of the two waves which is a standing wave.  Any wave which is a mix of traveling and standing or is pure traveling or pure standing can be broken down into forward and reflect components.  The standing wave stands still along the feedline and has nodes and loops alternating each 1/2 wave length.

In the example above where the wave travels out to the antenna and some reflects; the standing wave builds up gradually (although the buildup is over in microseconds).  Eventually, the transients are over and the wave takes on its permanent characteristic.  This is the wave we measure in our antenna tuner.  The transients occur each time we key the transmitter but are quickly over, long before we take our measurements of the steady-state forward and reflect waves.

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"PICKET FENCING on 2 METERS"
by Pete, NEØT

Have you been in your car on the air and noticed the so-called "picket fencing" where the signal seems to turn on and off quickly as though you are hearing it through the staves of a picket fence which you are driving next to?  If you slow the car you will find that the signal rises and falls slower as the car slows and even stops changing when the car stops but moving the car slightly changes the signal strength again.  In fact, when I used to sit in a Denver parking lot during the Wednesday night net I would notice that moving only a few feet would drastically change my signal strength.

Here's an explanation of what's happening:

It is a fact that when two rf waves are traveling in opposite directions they add to a standing wave. This is a very familiar fact to hams who use antenna tuners on HF to measure the forward and reflect waves on their coax.  Either on your coax or as RF signals, waves can either be "pure traveling", "pure standing" or a mix of traveling and standing.  In any of these cases they can be represented by breaking them down into the sum of forward and reflecting pure travelling waves.  A standing wave is one that doesn't move but stays stationary stretched over its wavelength next to your car (but still oscillates in-place up and down in amplitude).  At 2 meters the standing wave is around 6 feet long and it has both nodes and loops which are stationary (as discussed in the ARRL Antenna Handbook).  At a node the wave has zero value and at a loop has maximum value.  Therefore, as you move your car from a node to a loop the signal strength varies from zero to max.  In one 6 foot wavelength the standing wave varies like this: node(zero signal), loop(positive max signal), node( zero), loop(minus, max signal), node(zero again).  So the signal goes from zero to maximum each 1/2 wave.

So when is the most likely time for the waves to travel in opposite directions?  Not when you're near the repeater.  Near the repeater the wave is very strong in the direction from the repeater toward the receiver, the forward wave.  The character of this wave is that of a pure traveling wave.  When we are near the repeater the opposite traveling wave, the reflect wave, (called the reflect wave because it has bounced off a hill or something) is much weaker than the forward traveling wave.   There can be no picket fencing with a pure traveling wave.  However, far from the repeater the wave reflecting back toward the repeater can be nearly the same magnitude as the forward traveling wave.  The result is a wave which can have almost pure standing character.  This is when we notice "picket fencing".

The neat thing to know here is the distance between peak signals: 3 feet, 1/2 wave length.  On 70 cm of course the distance would be 35 cm, etc. just under 14 inches!

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IT IS TIME!
by Padre – WØWPD
(10/10/08)

Considering I’ve done this many times in a different venue I’ll do it again here! I mean preaching to the choir!

Now is the time (if not later than usual) to check all components in your antenna system.

Some of the following suggestions can’t be done very conveniently. I know that! But try!!! DO IT!!!

With summer behind us and winter on the way, often with wild excursions in temperatures and coefficients of temperature, besides humidity, remember the most important system of our station and/or our mobile operation needs to "serviced." --- the antenna(s).

Start at the rig, and work progressively through the switches, antenna tuners, bridges and everything between your rig and the antenna.

Coax connectors, and even screw terminal connections, have a nasty way of loosening and/or tarnishing. What happens is a high resistance contact. BAD NEWS!

Disconnect each coax connector. Pull out and re-insert two or three times before finally replacing and tightening the sleeve. The principle is the same with screw terminal connections. Be sure to tighten the terminals.

Regarding the aluminum (or whatever) antenna itself check the tightness of the clamps. Even mark the elements (for returning to the right place) and slide the elements back and forth to "clean" them. If you haven’t used an anti-oxidation "grease" for aluminum this is the time to apply a coating. Several are available at hardware and electrical supply stores.

DO IT!!!!

Now! After writing (and reading) this I better do the same!

73

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"THE DOCTOR IS IN"
(7/13/08)

Excerpted from:
The ARRL Letter
Vol. 27, No. 27
July 11, 2008

Question -- Don Christensen, W8WOJ, of Midland, Michigan, asks: I am not a frequent user of 2 meters yet; however, I do want to be available for emergency activity. I have a 2 meter handheld transceiver at the ready, but wonder what the preferred procedure is to ensure that my transceiver's nickel-cadmium (NiCd) batteries are charged and ready for service.  

The Doctor answers -- Unfortunately, NiCds might not be the best choice for such an application with intermittent use.  

If you run down a NiCd battery pack too low, any strong cells may reverse charge the weaker cells, damaging the weak cells. On the other hand they also don't like being constantly topped off without actual hard use -- this promotes crystal formation, which can short out the cells. They are most happy in applications in which they are used until they discharge significantly, but not all the way and then are just charged until fully recharged. Thus, the idea of having a spare pack that is just kept charged up, but never actually used, is not a good plan.  

If you have two packs, they will both last longer if one is used until it runs down and then you switch to the other and promptly recharge the depleted one. Perhaps you can have the radio turned on a few days a week monitoring the local repeater. 

Many handheld radios offer battery cases for non-rechargeable Alkaline cells that can be used in place of the rechargeable battery. These are a good choice since they have long shelf life, generally have a longer operating life than a charge with similar sized NiCds, and are usable in field situations in which charging sources are not available.  

Another choice, if you must have a rechargeable battery, is to use sealed lead acid or gel cell batteries -- they love to be kept on a float charge until needed, but are bulky and require a separate cable to the handheld.

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“REWARD OFFERED”
by HOWARD CUNNIGHAM ---WD5DBC

A REWARD OF 500 MICROFARADS IS OFFERED FOR INFORMATION LEADING TO THE ARREST OF THIS DESPERATE CRIMINAL: HOP-A-LONG CAPACITY.

THIS UNRECTIFIED CRIMINAL ESCAPED FROM A WESTERN PRIMARY CELL WHERE HE HAD BEEN CLAMPED IN IONS AWAITING THE GAUSS CHAMBER.

HE WAS CHARGED WITH THE INDUCTION OF AN 18 TURN COIL NAMED MILLIHENRY WHO WAS FOUND CHOKED AND ROBBED OF VALUABLE JOULES. HE IS ARMED WITH A CARBON ROD AND IS A POTENTIAL KILLER. CAPACITY IS ALSO CHARGED WITH DRIVING DC MOTOR OVER A WHEATSTONE BRIDGE AND REFUSING TO LET THE BAND-PASS.

IF ENCOUNTERED, HE MAY OFFER SERIES OF RESISTANCE. THE ELECTROMOTIVE FORCE SPENT THE NIGHT SEARCHING FOR HIM IN A MAGNETIC FIELD, WHERE HE HAD GONE TO EARTH. THEY HAD NO SUCCESS AND BELIEVED HE HAD RETURNED OHM VIA A SHORT CIRCUIT.

HE WAS LAST SEEN RIDING A KILOCYCLE WITH HIS FRIEND EDDY CURRENT WHO WAS PLAYING A HARMONIC.

 

For Those Who Understand, No Explanation Is Necessary.

For Those Who Do Not Understand, No Explanation Is Possible.

WD5DBC

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THE DOCTOR IS IN
(10/12/07)

Excerpted from:
The ARRL Letter
Vol. 26, No. 41
October 12, 2007

Question -- Ray Fritts, KA8SYX, of Jacksonville, Florida, asks: If a piece of coaxial cable has a specified loss figure in dB per 100 feet at a given frequency, does that mean that the loss in a different length of the same cable that is a fraction of 100 feet long is the same fraction of loss? For example, I have a type of coax that has a loss of 6 dB per 100 feet at 150 MHz. I have a 15 foot length I want to use as a feed line for my 2 meter mobile SSB transceiver. Does that mean that my feed line would have a loss of about 0.9 dB, not including SWR and connector insertion? I am particularly interested in the loss in received signal. Is my math correct, or is there a different method to determine the amount of signal lost in a coaxial cable when the length is different from that for which the published loss figures are expressed?

The Doctor Answers -- Your calculations are right on. That's all there is to it. But do keep in mind just a few potential pitfalls:

Published cable loss data is for new cable. If used indoors in a non-hostile environment, it will stay close to new for many years. If the jacket allows moisture or moisture vapor to penetrate, it can degrade from subsequent corrosion. I have been amazed to find that the copper in some old cables that have been used outdoors has turned black from corrosion, and likely is no longer acting like a shield at all.

You are correct that the loss increases with an SWR higher than 1:1. For your receive case, keep in mind that the SWR is determined by the input impedance of the receiver -- not the antenna impedance. Sometimes receivers aligned for minimum noise figure do not have an impedance of 50 Ohms. Check your receiver specs.

Do you have a question or a problem? Send your questions to or to "The Doctor," ARRL, 225 Main St, Newington, CT 06111 (no phone calls, please).

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NEXT SOLAR STORM CYCLE WILL START LATE
Experts Split Over Intensity
(05/29/07)

(excerpted from NOAA’S Space Environment Center release)

The next 11-year cycle of solar storms will most likely start next March and peak in late 2011 or mid-2012 – up to a year later than expected – according to a forecast issued today by NOAA’s Space Environment Center in coordination with an international panel of solar experts.

Expected to start last fall, the delayed onset of Solar Cycle 24 stymied the panel and left them evenly split on whether a weak or strong period of solar storms lies ahead, but neither group predicts a record-breaker. The Space Environment Center led the prediction panel and issued the forecast at its annual Space Weather Workshop in Boulder. NASA sponsored the panel.

“The Space Environment Center’s space weather alerts, warnings, and forecasts are a critical component of NOAA’s seamless stewardship of the Earth’s total environment, from the Sun to the sea,” said retired Vice Adm. Conrad C. Lautenbacher, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator.

During an active solar period, violent eruptions occur more often on the Sun.  Solar flares and vast explosions, known as coronal mass ejections, shoot energetic photons and highly charged matter toward Earth, jolting the planet’s ionosphere and geomagnetic field, potentially affecting power grids, critical military and airline communications, satellites, Global Positioning System signals, and even threatening astronauts with harmful radiation. These same storms illuminate night skies with brilliant sheets of red and green known as auroras, or the northern or southern lights.

Solar cycle intensity is measured in maximum number of sunspots – dark blotches on the Sun that mark areas of heightened magnetic activity. The more sunspots there are, the more likely it is that major solar storms will occur.

In the cycle forecast issued today, half of the panel predicts a moderately strong cycle of 140 sunspots, plus or minus 20, expected to peak in October of 2011.  The other half predicts a moderately weak cycle of 90 sunspots, plus or minus 10, peaking in August of 2012. An average solar cycle ranges from 75 to 155 sunspots.  The late decline of Cycle 23 has helped shift the panel away from its earlier leaning toward a strong Cycle 24.  Now the group is evenly split between strong and weak.

“By giving a long-term outlook, we’re advancing a new field—space climate—that’s still in its infancy,” said retired Air Force Brig. Gen. David L. Johnson, director of NOAA’s National Weather Service.  “Issuing a cycle prediction of the onset this far in advance lies on the very edge of what we know about the Sun.” 

On the Web: NOAA: http://www.noaa.gov/

NOAA’s Space Environment Center: http://www.sec.noaa.gov

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GOOD TIME TO CHECK
by Padre
(03/31/07

With the advent of good weather (I do hope) HAMS usually (should)? check all their antenna installations.

The winter weather can and does take a toll on coax, fittings, weather proofing, and antennae. One should be attentive to the “grip” of hose clamps, or whatever you use to secure the sections of the antenna. Likewise, the nuts and bolts of beam antennae can and do become loose and undependable.

When we find what seems to be a tight grip of the clamp it’s a good idea to test it by grabbing each side of the clamp to see if we can twist it loose. We should not be able to do so!!!! (If you’re going to do this it’s a good idea to mark the proper place for the joint).

Long wires, V-Beams, and vertical antennae, etc., are no less subject to the effects of winter.

Neither is the “weather proofing” at the coax connectors. Tape may become loose, dry out, or unravel. So may the “gunk” deteriorate. Any moisture getting into the connection will be very bad for your signal, coming or going.

Likewise, moisture creeping it’s way into the coax itself will do very serious damage.

In my sad experience wet coax never completely dries out. It is good for nothing but to be stripped of the outer jacket, and to salvage the braided shielding for use as ground straps among the equipment in your shack.

As a reminder: the antenna, with it’s feedline, is the most important part of your station.

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"BACKWARD SUNSPOTS" MAY HERALD START OF SOLAR CYCLE 24
(09/02/06)

Excerpted from:
The ARRL Letter
Vol. 25, No. 35
September 1, 2006

The recent appearance on the sun of two so-called "backward sunspots" may mean solar Cycle 23 is drawing to a close and Cycle 24 now is under way or soon will be. At least that's the thinking of some scientists.

"We've been waiting for this," said Solar Physicist David Hathaway of the Marshall Space Flight Center in Huntsville, Alabama, after the first backward spot showed up. "A backward sunspot is a sign that the next solar cycle is beginning."

The term "backward" refers to the sunspots' magnetic polarity. One such sunspot appeared briefly July 31, then disappeared, but its significance was that its magnetic polarity was just the opposite of current Cycle 23 spots.

Another more robust backward spot, Sunspot 905, appeared in late August -- although it subsequently began to dissipate -- and some sungazers are saying Cycle 24 already has begun. ARRL propagation guru Tad Cook, K7RA, this week called it "the second sunspot of the new Solar Cycle 24."

"Eventually there will be more of the new reversed sunspots than old ones from Cycle 23, and that occurrence is one way to mark the beginning of the next sunspot cycle," he said. Radio conditions will not improve any time soon but over a period of several years of the course of the 11-year cycle, perhaps peaking around 2010.

* * * * * *

FOR MUCH MORE AND INTERESTING INFO ON THIS WITH GRAPHICS, CHECK:

http://science.nasa.gov/headlines/y2006/15aug_backwards.htm

(Thanks to Dutch for supplying this URL).

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BATTERIES
by Mike Kendall --KCØATI

Secondary Type  (Rechargeable)

Lead Acid:

Variety of capacities 1 to 500 Amp hours.

Voltages 6 or 12 volts.

Two major types: liquid filled or gel.  The best type for use with ham equipment is the gel cells.  There is less of a chance for a acid spill.

These batteries like to be kept fully charged.  If the batteries are stored discharged the plates will passivate and this will destroy the battery.

Easy to maintain and best buy based on amp hours per dollar. Capacity loss is low in storage.

Nickel Cadmium:

One of the most commonly used batteries.

Voltage is 1.25 working voltage, end of charge should be 1.45 to 1.40 vdc. These cells have very good cycle life (>1000 cycles normally).

The only problem with Ni-Cad cells is the memory effect.   This effect can be erased by total discharging the batteries and shorting them down using resistors, then recharging. Capacity loss is 1% per day of remaining capacity in storage. Should be stored cold about 40 deg. F.

Nickel Metal Hydride:

Very common cell. Voltage is slightly higher than Ni-Cads.  They have more capacity than a Ni-Cad.  The charge voltage should be 1.55 at the end of charge.  These cells like to be used.  They have a lower depth of discharge capability than Ni-Cads.  The cycle life is very good (>1000 cycles normally).  The down side to these cells is the higher cost and the higher rate of self discharge.  Their self discharge rate is 3% per day of remaining capacity.  In other words charge them and then use them.

Lithium Ion:

One of the new battery types.  The working voltage is 3.00 to 4.2 vdc. These cells need  a special charger to charge them properly.  This type of cell should not be totally discharged.  The lowest cell voltage should not go below 2.5 volts under load.  If you short the cells or try and charge them backwards the cell has a protection device built in.  If the protection device is a fuse or the fuseable separator is tripped the cell is destroyed.  The cycle life of these cells is limited (<1000 cycles).  The self discharge rate is very low.  These cells can be disposed of by throwing them away.  The chemicals are very low in toxicity.

Lithium Polymer:

New type of battery.  The battery is made of two types of plastic plates that are pressed together.  There is no electrolyte in the pack. They are very flat and light weight.  The working voltage is 3.00 to 4.200 vdc.  These also need a  special charger to charge properly. They are normally used for low current applications.  They have a very low self discharge rate.  The cycle life is limited on these cells (<1000cycles).

ED NOTE: Mike has 20 years experience in the battery lab (Power Sources Lab) at Lockheed Martin. He knows whereof he writes. This information is very valuable to Hams when selecting HTs and batteries.