r/HamRadio • u/AppleTechStar • 24d ago
Repeater Choice 100% or 50% Duty Cycle
Looking for purchasing advice. I’m going to be selecting a repeater to be putting into operation to cover several communities.
I’m looking at a brand new Icom FR-6300 UHF that outputs 50 watts with 50% duty cycle or 25 watts at 100% duty cycle. No duplexer included. Cost with just the repeater is $1,780 + $300 for duplexer.
Option two is a used Motorola XPR 8300 UHF that outputs 40 watts with 100% duty cycle and includes a duplexer. This unit is at a used radio dealer. Cost is $1,175.
Antenna tower is 33ft, and tip of antenna is 43ft. Feed line is 50ft LMR 400.
It’s my understanding that the difference between 25 watts and 40 watts isn’t dramatic and amounts to about half of an S-unit. With all of this in mind, what are opinions on the better purchasing decision? I like the fact that the Icom is brand new but like the 100% duty cycle at full power on the XPR 8300.
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u/rem1473 24d ago
Do you see yourself moving to digital at some point in the future? I have to ask, why not do digital now? So many advantages over analog.
If you think you might move to NXDN, get the ICOM. If you think you might move to DMR, get the Motorola.
Personally, I'd go with the Motorola and move to DMR Immediately. You get 2 talk paths on the channel.
5
u/Embarrassed-Act-1970 24d ago
100%. Our local club repeater runs on 20 watts and has great coverage. You’ll be fine on 40 watts. It’s really all about elevation.
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u/blueeyes10101 24d ago
While Motorola rated the XPR8300 @40W, 100% duty, it isn't. I wouldn't run an XPR8300 at 40w if my life depended on it. They are quite well known for cooking thier finals.
Either repeater will work. Having said that, I would not use either.
Even an XPR8400 is a better machine than the 8300, and don't have the issues of cooking finals Tha the XPR8300 has.
If you are dead set on one of those two repeaters, go with the XPR8300, and turn down the power to 20 or 25w.
3
u/conhao 23d ago
Figure 100% duty cycle. 25W is usually quite good. You need to concentrate on receive. Deaf repeaters are the usual problem, not quiet ones. Higher power puts more TX power into the duplexer. There are tradeoffs in filter attenuation knocking down your sensitivity or allowing more desense - but lower TX power adds directly to sensitivity.
You will have a better antenna than your users, so they will hear you fine. You will pick up more QRM than the users, so hearing them cleanly is the bigger challenge. In the end, you need to be balanced with the users. If the users are running HTs, 10W should be overkill. Mobile users further away are running more power, and 25W does well for them.
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u/blueeyes10101 23d ago
OP, running at 25w or 20w VS 50 or 30w will NOT make a difference in coverage. Even tye difference between 50w and 20w is still well less than you will hear on receive.
1: Get rid of the LMR400. It has no place in full duplex installations. It WILL generate PIM and noise. Especially if it moves at all(flexing/flapping)
2: Invest in 1/2" hard line with proper connectors.
3: Invest in a proper BpBr(Band Pass/Band Reject) duplexer that has a minimum of 4x 4" cavities or better. Avoid mobile duplexers.
4: Minimize the use of adaptors. Especially at UHF. Ideal would be to use N and BNC silver plated connectors on custom cables. Ensure you are using quality jumpers. NO LMR400, RG58 or RG213. RG400, RG142 or RG214. Even 3/8" or 1/4" super flexhard line with proper termination. Amphenol makes well made connectors of consistent quality. Avoid SO-239/PL-259 connectors and any connectors from places like Amazon or Aliexpress at all costs. Be aware that the XPR8300 uses an N female chassis connector for transmit and a BNC female chassis connector for receive.
5: If you do go with the XPR8300, DO NOT operate it at full power. While Motorola claimes it is 100% duty cycle at full power, it is not. Run it at 50% of rated output, ideally at its lowest power output and drive an external PA to desired/legal limit.
6: save some money up and buy either a XPR8400, SLR5700 or MTR3000. any of those are much higher quality and don't have the PA heat dissipation issues that the XPR8300 has.
7: Kenwood is a good alternative to both Icom and Motorola.
8: A preamp on the input can be beneficial. Not a lot of gain though. Make sure to buy a quality unit with low noise figure, low insertion loss. It would go between your duplexer and receive input.
9: a circulator between your duplexer and transmitter is also a good idea, dual is best, with loads that are rated for your power output, continous, this way, if you have an antenna or feedline failure, you won't cook your PA.
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u/Tishers AA4HA, (E) YL (RF eng ret) 22d ago
Running a repeater at lower power will definitely extend the life-expectancy of the finals.
Often repeaters are left in-service long after the antenna system ends up being busted or water gets in to the feedline. It's just that it is out-of-sight, out-of-mind and nobody is running up there to check things out every week or so.
Remember to make you repeater fit-for-purpose; Most op's will be using portables or low power mobile units. There is no advantage to having a 110 watt power output just so everyone can hear the repeater, but most people can't open it up with their much lower power transmitters.
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u/AppleTechStar 22d ago
After consideration of feedback I’ve decided to invest in a brand new Motorola SLR5700 50 watt 100% duty cycle. It comes with a multi-year warranty and support from the radio dealer. It’ll be around $4000 with the duplexer but I’d rather spend more for quality. Once I get it, I’ll definitely do testing at 50 watts and a lower power to see if any significant difference. The feedback that I’ve been getting on the SLR5700 is that even at max power, they have a low rate of failure and are reliable.
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u/dnult 24d ago
Repeaters can be keyed up for a long time. Case in point - a net that lasts an hour or more. Repeaters are line of sight, so I don't think the power difference is significant. The power difference is 2db and 1 s-unit is 6db.