On Wednesday, January 22, 2014 4:32:31 PM UTC-6, Irv Finkleman wrote:
Q. Is there a relationship between the efficiency of an antenna and the

received signal strength?

Signal to noise ratio, very little. Received signal level vs
a more efficient antenna, can be quite a bit. But if the s/n
is appx the same, no biggie.. Lower level on the S meter, but
things should sound about the same when listening to it.





Just pondering on the matter. Because I have to operate with

restricted space antennas, usually with low efficiency, I wonder how

much of a relationship exists between Efficiency and Received Signal

Strength?

It all depends what freq, type of operation, etc.. But for general
skywave HF, even a fairly inefficient antenna can be quite fine
for receiving in many cases. The level may drop with the inefficient
antenna, but assuming the same basic pattern, the s/n ratio should be
pretty much the same. If you have enough antenna to increase the
background noise when connecting the antenna to the radio, it should
be fine for general gov use.




This leads to more questions such as how much do radials contribute

to efficiency?

Quite a bit, but that's much more a transmitting concern than receive.




IF that isn't enough, how much do radials contribute to the bandwidth?

In general, adding more radials will decrease the bandwidth.



For starters, I will be operating using an MP-1 antenna and a Yaesu

FT-817ND. I also have an MFJ-931 Artificial Ground, but propose

attaching the radials to the feedpoint on the MP-1. I intend to cut four

radials for 20M and spread them around the base of the antenna in

my room, and once the weather warms up, I'll try the antenna out on

the balcony with the radials spread around whatever real estate it

provides.

You would be much better off ditching the vertical idea, and
try to figure out a way to string up a simple dipole for
one of the higher bands.

If you have room for radials, you should have enough room for
a simple dipole. And it doesn't have to be inline, or in any
particular orientation. For 20m, you could have a feed point
in one of the corners of a room, and have one 16 ft leg running
along one wall, and have the other leg running down the other
wall. The legs would be 90 degrees apart, but will still work
fine overall. The antenna will be efficient if fed with thin coax,
and likely beat the pants off most small vertical rigs.
But this sort of assumes there is not wiring or metal in the walls
to grossly detune the antenna.
In your case, receiving should be no problem. Even a length of
random wire will work for general HF. Your real issue is radiating
enough RF for people to hear you.

One thing about "short" verticals. A good ground/radial system is
more critical for those than it is for full length monopoles which
can often get by with no/few radials and still work well enough to use.
That's much harder to do with a very short loaded vertical.

If I were you, I'd be trying to find ways to run sneaky dipoles.
You could use real thin wire if needed to make it less visible.
If you stick to the higher bands, they won't be too long.
You can do 10m nicely if you can find a way to string up 16 ft of
wire total. Even a 32 ft 20 m dipole can be fit into many rooms.
Feed with thin coax, and no tuner, no tuner loss, and the efficiency
will be high. That's what you want with QRP.