realllllllllly long coax loss report

[209 first class]

i was always curious to really know how much loss i would get with reallly long coax, so i had a chance to experiment with some i bought for a new antenna setup. i have a 285 foot length of lmr 400, i put it in line between my usual antenna /coax and noted the difference with a local base 30 miles away. (this guy is great for tests, he is long winded,lol). he was giving me 7 on the meter normally, and with the extra coax inserted he went to 5.6 on the meter. almost 1 1/2 less ! now i am wwondering if the long coax will outweigh the benefits of having the new antenna at 75 feet versus the old one at 38 feet with only 75 feet of rg8x skinny stuff. in other words, if i gain a pound and a half from the antenna being higher, i will just lose it due to the lonng coax. we shall see ! (does anyone have longer coax??)(the darn tree is about 200 feet from the house)

[lonesome 500]

lmr should be .7 db per 100' at 30meg........

i'm running 144' of 213 with my ant at 75'..........noooo prob

[drdx]

Well they say that coax running up has no loss. Not true of course, but you get the picture. At the .7 per 100ft, your 285 should come in at a 2db loss(what's that in theory, 1/2 and s-unit?), a loss that I would think would be more than made up for if the next antenna is significantly higher. How much higher will it be, feedpoint to feedpoint? Will it be the same antenna, and if not, what are you changing from and to? I do find it odd that there was that much of a drop when you did your test, but that does sound like a good way to test. -drdx

[lonesome 500]

I do find it odd that there was that much of a drop when you did your test, but that does sound like a good way to test. -drdx

a good test......to a point ....except for the constantly changing electrically charged layers of the atmosphere we use.

even that should be minimal

[TwentyTwo-Zero]

You mention a "new" antenna, but didn't say what you are using now or changing to. Since you are just about doubling the height of the antenna I would imagine that it would more than make up for the loss you saw using longer coax. "Height Is Might"...and I'm sure your RX/TX will improve because of it...

[Pillpopper]

I would think there would be loss with running that long of a coax but wow that is quite a bit. Nothing that an amp/ w a preamp cant take care of

[drdx]

Hey, that LMR400, is it the actual times microwave stuff, or a knock off brand? I've heard a few negative reports (locally) about the non times stuff.

-drdx

[231]

Hey, that LMR400, is it the actual times microwave stuff, or a knock off brand? I've heard a few negative reports (locally) about the non times stuff.

-drdx

This would be my thinking/question as well.

Can you borrow an antenna analyzer to check for sure? The MFJ-249B will tell you approximate line loss...or so was the case with my set up. The [Please login or register to view this link] was helpful, but didn't really share the true story of what was taking place. The analyzer showed quite a bit more line loss than the calculator did, about 7db to be exact (a full S-unit). Sure enough, when I installed the new coax, both RX/TX came up a full S-unit.

[Midlander]

There are lots of radio shops and cable companies selling the knock off Times Microwave LMR-400. Watch out, that cable is crap.

[KW KID]

If you still have the old antenna up, get an antenna switch and toggle between antennas. That should give a perfect direct comparison. If you ask me, the I say the high antenna will do better, even with the extra line loss. (But isn't 75ft of rg8x about the same loss as 285ft of Lmr400 anyway?)

In regards to the 1.5 s unit change, don't assume that is 7 to 9 db like we all estimate (5 to 6 db per S unit). That is an ideal radio, which most are not. Most radios are non-linear in the meter reading, and I'll bet only 3 db or so will move your meter 1+ S unit in the 5 to 7 S unit signal range.

μV (50Ω) dBm <30Mhz dBm >144Mhz
S9+60dB -13 -33
S9+50dB -23 -43
S9+40dB -33 -53
S9+30dB -43 -63
S9+20dB -53 -73
S9+10dB 160 -63 -83
S9 50.2 -73 -93
S8 25.1 -79 -99
S7 12.6 -85 -105
S6 6.3 -91 -111
S5 3.2 -97 -117
S4 1.6 -103 -123
S3 0.8 -109 -129
S2 0.4 -115 -135
S1 0.2 -121 -141