HFU HF Underground
Technical Topics => Equipment => Topic started by: Matt285 on February 09, 2020, 2010 UTC
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I'm sure this has been covered, but I'd like recommendations for coax feed to a 2m/440 antenna. The run will be 25 to 50' long. Transmitting. RG-213 comes to mind.
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I'd head straight to rg11 or whatever the thick cable tv coax is.
That is, unless lma or the better rg stuff like 9913 is in the budget.
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If RG213 is what you have, go ahead and use it, but be aware that at the higher frequency (440) you will lose
nearly half your power in a 50' run. 9913 has much lower loss but is hard to work with due to the stiff #10 solid
center conductor. RG8/U Belden 8237 would be a good compromise, easier to work with and less loss than RG213.
RG6 is another possibility if the 75 ohm impedance isn't an issue.
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I'd use LMR400, less than half the loss of RG213 at 440MHz. 1/2" heliax would be ideal, but you really don't save much loss for the cost difference.
+-RH
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I'd use LMR400.
+1
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Thanks for the input. I will go with the LMR-400.
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I recommend LMR-400 UltraFlex. Much easier to work with and has low loss at UHF:
https://www.timesmicrowave.com/Products/Cables/LMR_%C2%AE_High_Performance_/LMR%C2%AE_Ultra_Flex/LMR%C2%AE-400-UF/ (https://www.timesmicrowave.com/Products/Cables/LMR_%C2%AE_High_Performance_/LMR%C2%AE_Ultra_Flex/LMR%C2%AE-400-UF/)
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I recommend LMR-400 UltraFlex. Much easier to work with and has low loss at UHF.
Yes it is nice stuff but it's usually 1.5x the cost and technically not as low-loss as regular LMR-400. Availability can be an issue too.
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Yep, that .6 dB/100ft. is killer. 1/10 of an S unit. Gonna make a big difference on the repeater ;D WAY easier to string up.
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Yep, that .6 dB/100ft. is killer. 1/10 of an S unit. Gonna make a big difference on the repeater ;D WAY easier to string up.
This is why I went with RG6 vs LMR-400 for my discone. A few dB extra loss over the length of the run. I have a 4:1 splitter that I can connect here in the shack to feed 4 radios, with a 6 or 7 dB reduction in signal of course to each radio vs directly connecting the antenna to one radio. I can just barely hear the difference even on very weak signals.
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This is why I went with RG6 vs LMR-400 for my discone. A few dB extra loss over the length of the run.
Perhaps on HF but on UHF+ it's terrible. If size or weight is a major issue for you then go with LMR240. It's a good compromise for DC-1300 Mhz.
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So I ended up getting my hands on 40' of 1/2'' 50 Ohm Hard line (free) Just had to order connectors. It doesn't get much better for gain etc, but man this stuff is hard to work with. I kinked it twice before getting my cut. I'm nervous about using it. Gonna take my time and bend it as smooth as possible when needed.
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So I ended up getting my hands on 40' of 1/2'' 50 Ohm Hard line (free) Just had to order connectors. It doesn't get much better for gain etc, but man this stuff is hard to work with. I kinked it twice before getting my cut. I'm nervous about using it. Gonna take my time and bend it as smooth as possible when needed.
Brave man. On my permanent HF vertical I'm using 100ft of LMR-600. It's crazy stiff when new. That was a project. At that time, the price wasn't too bad so I ordered it with PL259 connectors. I think the connectors were like $15 each. I can't complain about the results though.
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Even though its better I'd rather be using LMR-400 instead. Can't argue with the price though.
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As long as it works, it's all good
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The good thing is it'll outlast the grandkids.
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Yes.... If I don't kink it.
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Yep, that .6 dB/100ft. is killer. 1/10 of an S unit. Gonna make a big difference on the repeater ;D WAY easier to string up.
This is why I went with RG6 vs LMR-400 for my discone. A few dB extra loss over the length of the run. I have a 4:1 splitter that I can connect here in the shack to feed 4 radios, with a 6 or 7 dB reduction in signal of course to each radio vs directly connecting the antenna to one radio. I can just barely hear the difference even on very weak signals.
I often marvel over discussions of signal loss. Some people will agonize over a tenth of a dB loss in connectors and others go “yeah....6 dB....that’s only an S-unit...I can live with that...”
And they are both right. It is all situational.
If your link has plenty of margin, a little extra loss is no big deal. If you are on the hairy edge, it can be a deal breaker. If all you listen to is your local NWS station, almost any antenna will work. If you are trying to hear one 300 miles away, you need a better antenna and feedline.
If you perform a link calculation for a free space path, a 3 dB increase in signal will increase your range 1.41 times. In practice (where a lot of other factors are also in play) you probably won’t see that, but you might see something on the order of a 20% increase in range. Would you notice a 20% range improvement on a daily basis? Maybe not, particularly on analog modulations where you are subjectively trying to decide whether signals are better or not.
For digital signals, 3 dB can make or break you depending on how much link margin you have. The BER curves for common error correcting code modulations are steep. If you are on the wrong side of the curve you get nothing, an extra dB might push you far enough to the other side of the curve to give you near perfect copy. This effect is well documented in the LMR industry where digital modulation (P25, DMR, etc) has firmly taken hold. Weak signal intelligibility is either good or non-existant.
The big reason to worry about every dB is because losses are accumulative. You might spend extra money for better transmission line and then throw the additional gain away by using poor connectors.
If you are designing for situations where you expect to work with marginal signals as a matter of course (e.g. radio astronomy, EME, etc) you are going to chase every dB. If you are putting up an antenna system for casual listening, you can be more willing to make compromises.