HF receive antenna installation

[zguy1243]

I have never put too much thought into my HF receive antenna, not where near the amount I have put into VHF/UHF. I have always used random wires with fair results. Right now I am using a 50 foot random wire antenna hanging maybe 25 feet above ground in a tree. I have located the antenna on a hilltop about 500 feet behind my shack and about 75 feet higher in elevation. The antenna wire is connected directly to center conductor of coax cable. Very crude, nothing fancy. I am looking for suggestions to improve my noise floor. The reason for locating the antenna 500 feet to the rear of my property is avoid mad made noise from local houses. Moving the antenna to this distance has helped much with man made noise but some still exists. Would I see any improvement in grounding the coax shield at the antenna or at the building?

See attached drawing

 

[SCPD]

I am using a 50 foot random wire antenna hanging maybe 25 feet above ground in a tree. I have located the antenna on a hilltop about 500 feet behind my shack and about 75 feet higher in elevation. The antenna wire is connected directly to center conductor of coax cable. I am looking for suggestions to improve my noise floor.

Use an un-un to mate the antenna lead to the coax. By just using the coax, you just made yourself a 500ft random wire. As you have noticed, this will not help your noise floor.

Watch: https://www.youtube.com/watch?v=L4jGNFGN-RQ

You can make your own or just buy one here: Model 9130 - QRP 9:1 Unun 1.5 - 54 MHz 300 watts - Balun Designs

PS. With that length of coax run, you should definitely ground it at the shack entrance to a quality ground. If you can get a 8 or 10 ft ground rod there then don't bother. It has to be quality ground.

 

[ridgescan]

http://www.balundesigns.com/model-9130-qrp-9-1-unun-1-5-54-mhz-300-watts/

PS. With that length of coax run, you should definitely ground it at the shack entrance to a quality ground. If you can get a 8 or 10 ft ground rod there then don't bother. It has to be quality ground.

+1
Ground the braid to either a cold water pipe (with known continuity to earth) near the entry point of the coax to the home, or an electrical conduit going into the ground near the entry point.
Also, can you stop the coax run at 100', then run an inverted L from it, up vertically then out to the end? That might make an insane receive antenna.

 

[SCPD]

Also, can you stop the coax run at 100', then run an inverted L from it, up vertically then out to the end? That might make an insane receive antenna.

I would stick with his original version for the lowest noise floor.

PS. The quote Ridge posted should say "if you *cannot* get a 8 or 10 ft ground rod in there...

PPS. And on the un-un you would only use the primary wing nut.

 

[AC9BX]

For HF listening a great choice is the TTFD (a.k.a. 2TFD or T2FD), this is the tilted terminated folded dipole. It doesn't need to be tilted but reception is more omnidirectional if tilted. If there's a particular direction wanted then a horizontal layout is fine. It's just wire with a resistor in the middle (terminated) of the folded section. It is not very efficient, there's a resistor in it after all, making it not particularly sensitive and a rather poor choice for transmitting (plus one is limited by the power handling of the resistor). But for listening it's quite a good antenna. It is very wideband covering all HF above the design frequency and respectable bandwidth below for receiving only and can be improved with a tuner. So make it as big as you can. It's high impedance, about 400 to 500 ohms. This means you need a flat twin wire feeder or an impedance matching transformer. About 9:1 is good, 450 divided by 9 is 50 making a good match to coax. The resistor value can be tweaked to get the best match for your installation. 390 Ohms seems to be a happy value. Being a folded dipole and high impedance makes it a very quiet and forgiving antenna. It rejects noise very well and is barely bothered by proximity to other objects so it doesn't care much if it's too close to the ground or trees or towers and such. Signal is low but noise is lower.

 

[prcguy]

I would use a center fed dipole around 100ft long with balanced line all the way to your house and a 1:1 choke balun to transition to coax near the radio. Your RG11 run may show minimal loss for 500ft at HF like 1.5dB loss @ 10MHz on a spec sheet but since the match at the antenna will be horrendous at most frequencies you could have 20dB or more loss in the coax because its being used in an extreme mismatch condition.

500ft of 450 ohm ladder line will have minimal loss under mismatch condition and will work much better. The only caveat is you have to keep it off the ground but a foot or so is probably fine.

I've used T2FDs from 90ft to 165ft long and they are quiet for receiving. A 12:1 balun is best (as used by B&W) and the terminating resistor is usually in the 600 to 800ohm range.
prcguy

 

[Fast1eddie]

Sounds good, but I only have 50 feet to work with and cannot run out into the yard, have to keep it below the roofline. Only surface to install insulated standoff mounts is aluminum siding. Wondering what significant effects (if any) it would have. Thinking it might act as a reflector.

Good Signals, Ed N3KEX

 

[k9rzz]

Might act as a reflector if it's 0.2 wavelengths away. Put up whatever you can, use it, and go from there. Improve where possible.

 

[nanZor]

Depending on what bands you listen to, a 4:1 Un-Un may be a better choice.

Definitely ground it near the antenna and at the house. As it is now, the common-mode of the coax shield (rf skin depth facing the real world) is acting as a 450 foot long radial on the ground. Eh, ok but you may want to run actual radials out from the feedpoint.

Consider placing an RF choke, like the MFJ 915 or better out at the feedpoint.

While grounding is good electrically, it may not be a sufficient RF ground, and the choke will also serve to choke noise coming FROM your shack and traveling out to the feedpoint and coming right back down inside. Go with some radials if you can.