When tuned through a tuner, the 80 meter dipole does not seem to work as well as the 40 meter dipole does on 40 meter receive, so I tend to think a low swr at the antenna seem to work best for receive, and makes a big difference.
You're not telling the whole story. Not all dipoles are created equal. Did you observe this using coax-fed dipoles, or balanced-fed dipoles? Sounds to me like you're talking about a coax-fed dipole, which does not perform well outside its intended band. Dipoles fed with open-wire line perform every bit as good at their harmonics as they do at their fundamental.
The fatter the antenna, the wider the bandwidth, someone is selling strapping with stainless wires in it to make dipoles out of, that is supposed to be very broad banded.
Even in AM, you're only utilizing about 10-12 kHz of spectrum at any given time. If you have a tuner, you don't need a "broad-banded" antenna.
These so-called "broad-band" antennas are catering to a crowd that wants to buy an appliance, plug it directly into an antenna, and not have to do anything tedious like learning to operate a tuner.
They're selling to the misconception that "low SWR" automatically means a good performing antenna. You can prove this yourself by counting the number of QSOs where someone is told he's not coming in all that well, and he responds by saying he should be coming in just fine, because his "SWRs are very low".
VSWR is
not a measurement of an antenna's abilities. It is a measurement of resistive and reactive unity between a given transmitter and a given antenna, nothing more.
If you cut an antenna for 3850, its nice to be broad enough to cover most of the band with a low swr.
My current 80 meter dipole is under 1.5 to 1 at 3835 and 3885, made with #10 copper wire.
It seems nice, perhaps, but it's not necessary unless you're running a rig with no tunable output, no tolerance for mismatch,
and no tuner.
If you have a tuner (or a transmitter with a tuned PA), those numbers lose their meaning entirely. Then you no longer need to split hairs over your VSWR. Your transmitter will see a load matching its impedance, your antenna will see a source matching its impedance, whatever those are.
I also tend to think you dont loose much on TX if you use coils to shorten an antenna a little, say a 100 foot 80 meter dipole, I ran one years ago that was 100 feet, with some B+W coil stock over an insulator to make up for the 20 feet I was short.
That approach does not lend itself to multi-band use. You need to make sure the coils are nowhere near any voltage or current nodes. Too close to the current node, your coil may melt. Too close to a voltage node, the coil will arc and spark and throw trash all up and down the band.
Since your current and voltage nodes form as a function of wavelength vs. radiator length, a neutral point on one band may be a current or votage point on another band, especially if you're dealing with an oddball length like 100'.
I'd also recommend the horizontal loop, for 75 meter cloud burner, elevated only 20 feet should do a fine job.
Judging from his original post, it sounds like he's looking for something more than a cloud burner.
Patrick's question was "will a dipole outperform what I've got now". He can only hear one or two local guys and would like to be able to hear/work the rest of us.
So you might be wise to first check into what and where the noise is coming from.
Again, that's putting the cart before the horse.
The reason Patrick can't hear signals over the noise is because he's receiving on 40 feet of wire that's only 10 feet off the ground. Do the math: that's less than 1/6 of a wavelength of wire that's less than 1/24 of a wavelength above ground! I'm sorry, but you can't receive diddly-squat with that, even in the quietest of conditions.
Even if he had
zero man-made noise, his receive signal-to-noise ratio would still suck bogwater. It
seems like he has a noise problem, because he just plain isn't getting any signal out of anybody. Signal-to-noise ratio is just that: the ratio of
signal vs. noise. If you have an antenna that will never pick up any signals, chasing down noise is a waste of time, and will gain you nothing. You still won't receive worth a crap.
Like I said a few posts ago: if you use a coathanger to receive on 75 but all you hear is furnace blower noise, it's because your
antenna sucks, not your furnace.
Once Patrick has an antenna up that will start pulling in some signals,
then the noise issue (if there even
is a noise issue) can be addressed.
