07/02/2026
Members of the 49 Repeater Group, with the invaluable help from James (KB0NHX), traversed to the 145.490 "flagship" repeater on the N0NWS SkyWarn repeater network to make upgrades to the repeater system. The existing Vertex VXR-7000 repeater, CAT-1000 controller with RLS-1000 remote link switch, Samelex power supply and TE Systems 350-W amplifier have served the system well for just over 26 years.
The 49 Repeater Group was blessed with a grant from the ARDC group to purchase new equipment for all N0NWS repeater sites and on July 1, 2026 the 145.490 repeater system was the benefactor of nearly $11,500 worth of new repeater equipment as the system got a complete upgrade with all new equipment and grounding.
The new "standard" Motorola SLR-5700 repeater was installed and acts as the system receiver and exciter. A new Crescend 250-Watt amplifier that runs on 48vdc was installed along with the matching 48vdc, 25a Duracomm power supply. The amplifier only draws about 12a at 48 VDC which means it will run more efficiently, and thus cooler, than the old equipment. The new power supply is simply loafing at just 50% capacity. The CAT-1000 controller was replaced with the new Raspberry Pi based controller which will allow for remote programming and audio adjustments as well as remote alarm monitoring of the Motorola repeater. In addition, two Bird 4521 power meters were installed on the output allowing simultaneous forward and reverse power measurement that can be viewed by the control operator at any time to verify transmitter and transmit antenna performance!
The increase in the RF environment over the past several years has led to several unresolved interference issues due to mixing with the repeater transmitter, de-sense to the receiver from the repeater transmitter, and, after what we saw today, a high level of RF being induced directly into the receiver from the 30 kW ERP radio station transmitter located on the same tower! To resolve these issues, a new 2-cavity, high-Q bandpass/band reject filter from TX RX was installed on the receive side of the system. The passband will ensure only frequencies on or near 144.890 will be passed onto the receiver. For reference, the repeater's receiver level for 12 dB SINAD is 0.20 uV without the filter and 0.23 uV with the filter. This equates to 1 dB of loss in sensitivity. However, the passband filter now filters out 223.07 uV of signal constantly bombarding the repeater's receiver from the co-located radio station transmitter. When you are dealing with small numbers like 0.23 uV, eliminating the 223.07 uV signal is huge! In addition, the filter arrangement notches out the 145.490 transmitter to the tune of just over 90 dB. What we found during testing without the filter was that the repeater's transmitter was actually de-sensing the receiver by 1 dB. Therefore, the 1 dB of loss from the filter is offset by reducing the 1 dB of de-sense from the 145.490 transmitter making it a "wash" in the grand scheme of sensitivity.
What we gained was a very large amount of selectivity which is VERY important in any repeater system. We expect the mix that occurs on Monday nights from the NCS on the 146.865 repeater to no longer happen because of the bandpass installed on the repeater being much narrower and the notching of the transmitter in case there is a mix in the receiver that involved the transmit frequency. We had also identified a mix that occurred when the 145.490 transmitter, the 146.685 repeater in Springfield and the 145.290 repeater in Bolivar were all transmitting at the same time. By notching out the 145.490 transmitter at the receiver, this should eliminate that problem as well. By adding such comprehensive and quality filtering to the receiver, we have likely eliminated many other mixes that have occurred over the years that have possibly never been identified.
With all the technical talk, what does it equate to for the end user? We expect handheld and mobile users to be able to access the 145.490 repeater much more easily. For example, one user located about 30 miles from the repeater site previously had to be outside with 5-Watts to access the repeater on his HT. Now, however, the same operator can access it from inside his residence on just 1/2 of a Watt! The 145.490 repeater has always been an alligator with it's huge 350-Watt amplifier which was operating at 340-Watts upon arrival. Now, at the 253-Watt level that we are running, we expect most people will not notice much of a difference hearing the repeater but they will have a much better signal into the repeater making it more of a matched system. When the system was designed, it was meant to have more power to allow HT's to hear it better in buildings and especially in Springfield. However, with the additions of the 145.330 and 147.285 in Springfield as well as other repeaters throughout the region that type of power is no longer needed to try to get to people listening on HT's allowing us to match the system transmit and receive more effectively.
Lastly, all site equipment has been properly ground with #6 ground wire to every piece of equipment to a 19" rack mounted copper ground bus which has a #2 stranded ground wire that connects to the site's extensive ground system. The site's coax lightening arrestors have also been grounded to the site's ground system as we attempt to protect the new equipment. We have a few items left to address that we didn't have parts for today and hope to get them wrapped up before the fall storm season begins.
We'd like to thank everyone for their patience as we worked through a plan to improve the 145.490 repeater and we expect years of reliable operation of our newly installed system!
(This write up was graciously written by James, KB0NHX, to explain all of technical details of the testing, evaluation, and work preformed. The 49 Repeater Group cannot thank James enough for his partnership!)
- 49 Repeater Group.
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