HAM’S LIFE

While the issue of interference between amateur radio operators on the 440 MHz band and the US Air Force Pave PAWS has been resolved on the east coast the restrictions on amateur operations on the 440 MHz band still remains in effect on the west coast of the United States. 

If you are not familiar with the issue more information can be seen on the January 8, 2008 post (http://hamslife.com/?p=60) and on the February 1, 2008 post (http://hamslife.com/?p=81 ) of this blog site. 

By means of email the Section Manager for the ARRL Sacramento Valley Section, Ronald D. Murdock, W6JK gave an update to ARRL members in the Sacramento Valley Section. 

In his email Ron said that on 8 January 2010 he and other ARRL officials were given a briefing by Lt. Col. Cory J. Keepler the commander of the 7^th Space Warning Squadron at Beal AFB, CA.  In this briefing Lt. Col. Keepler revealed that the Air Force believes the current restrictions on the local Amateur radio operations has improved Pave PAWS operation and thus will remain in effect. 

There is also some other interference which the Air Force has not yet been able to identify.  The Air Force will continue to search for any interference and hopefully will be able to identify all of them. 

On October 20, 2008 the ARRL petitioned the FCC to modify or cancel the authorization it gave Digital Aurora Radio Technologies (DART) to operate on the frequencies of 7.10 to 7.60 MHz with its experimental station WE2XRH.

DART requested the Federal Communication Commission (FCC) grant them a two year authorization to transmit on the 5, 7, and 9 MHz shortwave bands using Digital Radio Mondiale (DRM), a digital technology that can give near FM broadcast quality on bands below 30 MHz.  The transmitter to be used has an output power of 100 KW and with the gain antenna system the Effective Radiated Power (ERP) adds up to 660 KW to be operated within a 1500 KM (937.5 Miles) radius of Delta Junction, Alaska.  The request was honored by the FCC and they were allocated the frequency bands of 4.4 to 5.1 MHz, 7.1 to 7.6 MHz, and 9.25 to 9.95 MHz.

7.10 to 7.6 MHz includes 200 KHz of the 40 meter amateur radio band.  The DART DRM transmission is 20 KHz wide.  The interference potential to the 40 meter amateur radio band is obvious thus prompting the quick action by the ARRL to petition the FCC.  

On October 24, 2008, just 4 days after the ARRL submitted the petition, the FCC acted and modify DART’s 7 MHz band to 7.3 to 7.6 MHz.  This would amount to an extremely fast response to the petition if indeed it was a response to the petition.  The word is that the FCC caught the clerical error, made the change and the ARRL petition had nothing to do with their action.  The accuracy that it was an error correction may possible be indicated by the 4.4 to 5.1 MHz band change which had nothing to do with the ARRL petition.  The new frequency band is 4.5 to 5.1 MHz. 

There are some who say the petition was a moot point to begin with because DART has stated they will not transmit on any amateur radio frequency. 

There does not need to be any finger pointing or criticism given for the actions of any the three parties.

The ARRL is to be commended for their quick and decisive action.  If a wait and see attitude had been taken it could have created more difficulty for all concerned.  The action also set a precedence that could help prevent future encroachments on our bands by some who may not have a friendly attitude towards ham radio. 

The FCC deserves our appreciation for their quick action no matter what the reason is for their action. 

Finally DART should also be thanked for their attitude and promise not to interfere with amateur radio communications by not operating in any ham band.  Hopefully DART will not take the petition as an insult but will recognize it as just good stewardship of the frequencies we have been allocated.  There is a saying, “good fences make good neighbors” and in this case the fence between the 40 meter ham band and the 7 MHz DART band has a very good fence by not having any overlapping frequencies.

Hopefully DART will have great success in their endeavor to improve the quality of broadcast radio and to provide a reliable state wide broadcast communication system for the state of Alaska. 

When a computer, CD player, or some other non-tuned electronic system is affected by a transmitter it is usually not the fault of the transmitter. The same can also be said with tuned devices such as AM/FM radios and Televisions but there is a possibility of a transmitter defect can sometimes be the cause of such interference. It has been the hams who have been receiving the criticism for this problem for years but the real culprits are the manufactures for not using proper shielding to prevent such a problem. But blaming the manufactures does not get to the real root of the problem because people want inexpensive items and so manufacturing must cut corners to reduce the cost.

If an older transmitter with a class C final is being used then a good low pass or band pass filter should be used because class C amplifiers are rich in harmonics. Most transmitters today are designed to run SSB which requires a linear output that by nature do not have the high level of harmonics. Modern FM and CW only transmitters would be the exception.

The first thing that should be done when encountering such a problem, and this should be done whether or not a problem is known to exist, is be sure your station has a proper earth grounded. The ground at the power plug, that would be the green wire or half round hole of the socket, and cold water pipes are not a proper earth grounds. That green wire runs all though the house and works fine for 60 Hz but they are long and thus can act as an antenna to RF signals. Metal cold water pipes have joint compound to prevent leakage which can act as an insulator and many modern houses are plumbed with plastic pipe.

Drive a ground rod at least 8 feet long in the soil as close to the transmitter as possible. Run a wire 12 gage or larger using the shortest possible run to the transmitter. Flat braid is preferable to round wire conductor.

After assuring the ground system is good a ferrite toroid can be added to the transmitter’s power cord. If the transmitter uses an internal power supply then this would be the AC power cord but if it uses an external power supply the toroid should be used on the cord between the power supply and the transmitter. The toroid should be placed as close to the transmitter as possible. If an external power amplifier is used to boost the power of the transmitter then it too should have a toroid installed.

The toroid will need to be large enough around to pass the plug through and to take several wraps of the cord. Some modern units have the toroids already used inside the unit which will eliminate the need to add them externally.

If the problem continues add a toroid to the power cord of the affected device and to the cord of each peripheral device (speaker, monitor, printer, mouse, etc). The toroid should be placed as close to the affected unit as possible.

A high pass filter in the antenna system of a TV is sometimes helpful especially when it is working off an antenna rather then cable or dish.

The above instructions are for your own equipment. Be very careful about doing anything to a neighbor’s piece of equipment because if anything happens to that device they will probably blame you for the damage. A lot of times too when such devices are added people will say that it is just not as good as it was before even though there is no change.