CPRA NEWSLETTER APRIL 2016
IRLP
The IRLP was taken out of service 4/3/2016. The electrolytic capacitors in the computer were leaking acid indicating that catastrophic failure was imminent. A copy of the hard drive is being made and a replacement computer is being prepared. Sorry for the interruption but that model of a Dell computer has now been shown to be subject to failure due to age. That computer was twelve (12) years old and multiple models in that era had similar problems. The new computer will last longer.
This problem is prevalent on the following Dell computers:
Precision 340/360 Optiplex 240/260/270/280
These computers can be recognized by their “clam shell” style of case. That is, they have recessed buttons on the top and bottom that both must be pushed in and the case folded out from the hinge at the front of the computer. This capacitor issue is a known problem with those product lines and since much time has passed, these units are not in wide use. Our Optiplex 240 has performed flawlessly for many years and this problem was discovered during routine inspection and maintenance. For those that still use these computers, you may want to open your computer and check the electrolytic capacitors toward the back of the unit, close to the fan and processor, specifically looking for a bulged appearance on the top of the cap. This has the appearance of a “Jiffy Pop Popcorn” tin that was popular in the 1970’s. If you see the bulge, you have a problem that will cause motherboard failure . It’s time to start making your backups.
NOISE FLOOR IS RISING
The noise floor has been slowly rising at Blue Mountain. Higher noise reduces receiver performance. This noise is man-made and is not caused by nature. We are in the process of taking measurements at multiple sites to compare the noise figures.
We use the “effective receiver sensitivity test” which has been a Motorola standard for many decades. It is described as follows:
A calibrated signal generator is fed via an “Iso-T” between the antenna and receiver. A 50 ohm dummy load is connected to the Iso-T to simulate a no noise antenna environment. The amount of signal from the generator is raised to produce 20 dB of quieting (eliminate all the audible crackles) is the relative sensitivity of that particular receiver. That number is typically several hundred microvolts when taking into consideration the loss of the Iso-T providing the isolation from the signal source. Then the dummy load is removed and the normal antenna is connected to the receiver. At this point the signal is raised until the 20 dB quieting point is again reached. Subtract the second number from the first, preferably in dB, and you have the amount of noise user radios must overcome to effectively quiet the receiver.
Here’s the repeater-builder version of this test:
With 6 dB of noise the effective sensitivity is 0.4 microvolts.
With 12 dB of noise the effective sensitivity is 0.8 microvolts.
With 18 dB of noise the effective sensitivity is 1.6 microvolts.
With 24 dB od noise the effective sensitivity is 3.2 microvolts.
With 30 dB of noise the effective sensitivity is 6.4 microvolts
This is predicated upon a .2 microvolt for 20 dB quieting measurement when the signal generator is connected directly to the receiver under test.
At Blue Mountain we are experiencing 10 to 30 dB of noise depending upon exact frequency and band. UHF appears to be hard hit as is the one receiver operating in the 146 MHz band. (146.16/76) The receivers in the 144 MHz range are only seeing 10 dB of degradation.
When comparing Blue Mountain to another site such as Cornwall, only about 3-4 dB improvement was shown on VHF. Even this can be attributed to hot day, meaning solar output and atmospheric activity, not physical temperature. However, the greater degradation is worthy of investigation since the RF temperature of the site has fallen with the decommissioning of large analog television transmitters.
We are in the process of determining what is normal/acceptable/degraded/not acceptable with each station to create the best user experience for our members. When we know what we can expect for repeater performance and have historical baseline records from which we can compare results, we are in a better position to know if a commercial transmitter has potentially lost a harmonic filter or a power amp module has gone spurious or if we are seeing normal operation. There is no such thing as too much data in this instance. Additional data is being collected from multiple sources. The worst case solution would be to relocate receivers off site.
DIGITAL MOBILE RADIO (DMR)
Thanks to all that pledged funds for the purchase of a VHF DMR SLR5700 manufactured Motorola. The cost for the repeater with supporting parts and materials was $2200.
Please bring your checkbooks to the next meeting so these pledges can be collected and our supplier can be paid.
We are still a few hundred short of the $2200 goal so any additional pledges are very welcomed. We intend to install this repeater as fast as reasonably possible.
The final location for the best performance may be influenced by the noise floor at a particular site. The DMR repeater will have two channels available at the same time with time division multiplexing:
Local and Regional. Additional sites are being evaluated. This would extend coverage beyond Dauphin County.
PRESIDENT’S MESSAGE
The next meeting will be held on Thursday, April 21, 2016 at 7 PM at The Wharf in Harrisburg. This is a one of a kind meeting. Two authors from the Harrisburg area will be discussing their books on Broadcasting.
- “Images of America, Harrisburg Broadcasting”
By Tim P. Portzline, KB3MQL, 128 pages
Available from Amazon.com: “Harrisburg Broadcasting”
- “Brought to You By …”
ABC Sports, Field Operations, Lodi, NJ
A memoir by Dan Rapak, WA3ATV, 388 pages
Available from Amazon.com: “Brought to You By …”
Order a copy of the book and have the author sign it at the next meeting. Come early at 6 PM for food and drink.
If you had a General or First Class Radiotelephone, please photocopy that license and bring it to the next meeting. So many hams were influenced by that licensing. I was able to work summer relief for the most powerful AM radio station in Philadelphia (50,000 watts) because of that license.
The requirements for the engineering job were:
- Minimal Experience
- Radiotelephone First Class FCC License
- Ham License
I listened to rock & roll all day and they paid me.
CPIN CAMERAS
To view the cameras from the public internet:
username: cpin password: cpin
To view the cameras from the CPIN Network:
username: cpin password: cpin
No more software updates until they have been released at least six months. The last update was a disaster.
LANCASTER RADIO TRANSMITTING SOCIETY
(LRTS) CAMERAS
To view the cameras from the public internet:
username: lrts password: lrts
To view the cameras from the CPIN Network:
username: lrts password: lrts
VOIP TELEPHONE
To view the phone directory from the public network:
at the bottom
To view the phone directory from the CPIN Network:
Instructions at the bottom
Don’t forget to look at “Favorites” in the upper right corner.
Many sites that might be needed in a disaster are located there.
DUES
It is time to pay your dues for 2016. You will be receiving a notice if you currently are a member. We need your support to maintain the equipment. Contributions for capital improvements are very much appreciated. If you are not a member and wish to support the club, please fill out and return the attached form.
POSSIBLE FUTURE MEETINGS
- Evaluation of potential DMR repeater locations in adjacent counties including Longley-Rice signal plots and noise floors.
- Tour of WTPA Studio
- Remote HF Radio via public internet and CPIN Network