LMR-400 coax

Kramster

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Hi - I don't know if this question has been answered before but I'll give it a shot!
I have an ICOM R-75 and an Alpha Delta DX-CC multi fan dipole at about 15' at the apex. I'm using RG-8X coax for now but I'm considering getting LMR-400 coax. Will I hear any improvement in reception if I also raise the antenna another 15' or is the LMR-400 more suitable for amateur radio transmitting?
 

ka3jjz

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LMR cable for HF receiving is way overkill. Raising the antenna might help somewhat, but I suspect the gains will be minimal. Propagation is largely influenced by solar activity, and right now, it's in the dumpster.

The DX-CC is primarily tuned for the ham bands; while it will work outside of them, it will not work nearly as well. What is it you're trying to hear? How much space have you got for antennas? Mike
 

jhooten

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How long? Anything under about a hundred feet you will never notice the difference.

Raising will help. From 15 to 30 feet not a lot but some, depending on the frequencies you want to monitor.
 

Kramster

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I'm on a small city lot - My backyard is about 90x40'. I'm mainly interested in the SW bands, and some ham bands, and I thought that the DX-CC would be a good compromise antenna.
I can get it up to another 15' so that might be might best move.
Thanks!
 

prcguy

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At 15ft above the ground mostly horizontal the DX-CC antenna radiation pattern will be mostly straight upward and best for several hundred mile radius NVIS propagation below about 10MHz. Raising it to 30ft will improve its efficiency in NVIS mode and will also help some with distant reception coming in at low angles.

If you have less than 100ft of coax you will probably not benefit from an LMR400 upgrade. You would see a little improvement at the 30MHz end of the spectrum but that's about it.
 

ka3jjz

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There's a lot more to hear on the HF bands besides hams (which is what the DX-CC is tuned for) - and better widebanded performance, too. For an example you could get a PAR end fed, replace the 45 foot of wire with 90 foot, and I suspect you would find better performance on frequencies that are outside the ham bands.


You have some room to work with - this is but one possibility. Here's a couple more...



Don't be afraid to experiment. With propagation rather poor these days, it can be an advantage to have 2 antennas of different types. What isn't be heard well on one might be on another....Mike
 

vagrant

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Please remember about the directivity. The legs on my OCF inverted V run E/W so I RX/TX better N/S. The apex is at 36' for the reason prcguy noted and the legs never go below 6'. With this in mind I setup another OCF with the legs running N/S and mostly horizontal with a 36' apex as well. It definitely makes a difference, even if you only receive. Mike's advice about experimenting with an End Fed is something to try down the line. You could hoist up the line of an end fed to the apex so that it is perpendicular to your dipole and use a switch at your receiver.

My coaxial runs are 130' and 100', so I use LMR-400 as it has half the attenuation loss as RG-8X.
 

prcguy

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So you will need to raise your antenna and I would suggest two 70ft towers minimum to hold up the antenna. Since the coax run will get longer to reach the antenna on the towers you would then need an upgrade to LMR400. After all that you wouldn't want to use an old R-75 and will have to upgrade the radio to something better.



Alright! - Appreciate the info!
 

K4EET

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Kramster, as a general rule of thumb, keep in mind too that many antennas are going to be more or less directional with the exception of a vertical antenna which will be omni-directional. I also use Alpha Delta brand dipoles for my ham band antennas and like your Alpha Delta DX-CC, the main lobe for reception will be perpendicular to the direction the wires run in. By using multiple wire antennas; dipoles, off center fed, end fed, etc., and orienting them in different directions, you can achieve multiple reception angles and directions further maximizing your reception capabilities. Even a well placed vertical with a good ground system and due to what is known as the "take-off angle" of the radio wave (same for receive) will give you an even broader complement of antennas to select from to see which one is receiving your target signal better. Using a good coaxial antenna switch will make for a quick assessment of which antenna to use to receive your signal of interest. Have fun and experiment! Then as you learn about antennas and their characteristics, you will better understand how the different designs come into play with reception during times of poor propagation. In about 5 or 6 years, however, you will be amazed at how well signals are being received. Its the so-called sunspot cycle and right now we are at the worst possible part of the cycle. The good news is that things WILL get better from this day forward. Guaranteed! :)
 
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Ubbe

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My coaxial runs are 130' and 100', so I use LMR-400 as it has half the attenuation loss as RG-8X.
A RG8 attenuates 2dB at 50MHz for a 100ft lenght and LMR400 1dB. At 10MHz it's half of that. So choose wisely between a half dB and 1dB increase in performance to the additional cost. If you will do an inverted V antenna and have a mast pole for it you could put a VHF/UHF antenna on top of it and use a filter to mix in that antenna above 50MHz and use the same LMR400 coax. But you might already have the VHF/UHF antenna sorted out by other arrangements. At 900Mhz and 100ft it's a 12dB to 4dB difference.

/Ubbe
 

ka3jjz

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This is for HF, not scanner frequencies. At such a small difference, you aren't going to hear that anyway....Mike
 

MisterLongwire

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I agree. I have RG8 on my line and no problems, thinking about all the boohooing using LMR-400, whether for scanning, HF listening, or whatever. All my ham equipment use RG8 with no issues,
 
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