Update: replaced the 25 ohm WW pot with a 1 ohm 4 watt WW potentiometer,
with surprisingly good results. Am now able to pull in BBC Africa on 7160
kHz, although there is a somewhat faint high-pitch whine behind it. Still,
it is definetly intelligable. At least 1000% better than it was. When
attached to the external antenna, it is downright incredible. The only
thing I have trouble picking up with the whip is WWV at 5 MHz (and 2.5 MHz
is out of the question). With the external antenna however, these come
through like gangbusters. The acid test will come at 1300 UTC when I try
to pick up Voice of Korea. If I can pull that out of the noise, I will be
ecstatic. That is what I have been working towards since I started this
project. Oh, and it helps if all your wires are connected, and the one
carrying the RF to the input of the first amplifier stage is not hanging
loose, near it's intended connectionpoint, due to a broken solder joint.
Found that while installing the 1 ohm pot and had to go back and see how the
25 ohm pot performed once the wire was reconnected. Better, but still not
ideal by any means. Then installed the 1 ohm pot, and got surprised. If
you want to see the schematic, I can post it to
alt.binaries.schematics.electronic.

Hoping to hear from you again on how to improve reception further.

Thanks,

Dave

"Dave" wrote in message
...
Hello Cecil,

Thank you for the interest, and the question. Last time I had the RF
amplier on the scope and sig generator, it was giving me approximately 100
mV output with something that *looked* like a millivolt or two input
(possibly at much as 5 mV but no more), at 5 and again at 10 MHz. Now, I
am enough of an RF newbie that I *think* this is what you are asking, but
if not then please enlighten me. I think I understand the need for a
low-loss antenna tuner, which I am trying to improvise with a 25 ohm
wire-wound pot acting as an autotransformer, ala The Miracle Whip (QST,
July 2001 PP 32-35.) And it seems to be working to some extent, just not
in the ideal way I need. I am able to pick up Radio Nederlands on 6145
kHz (I *think* that's the frequency) off of the whip, but not BBC Africa
on 7160 kHz, even if the radio stops there and seems to realize that there
is something going on, but just can't pull it out of the mud. I am able
to pull in BBC Africa on 7160 kHz with the external 110' random-wire
antenna, and that with a bare minumun of noise. The whip however, just
gives me the noise. I am about to do some more experimenting with
different WW pots to see if I can get anything better. If all of this
sounds totally bat-****, please forgive. It does seem to work at least
half as good as I need however, and I am hoping to tease out the rest.

Please let me know if I am headed up the wrong creek with my answers.
Hate to say it, but am honestly making this up as I go along (obviously).

Thanks again,

Dave

"Cecil Moore" wrote in message
...
Dave wrote:
It's a 43 inch collapsable antenna (7 segments.) Maybe I just need more
amplification...

For maximum power transfer from the antenna to the
receiving load, you need a matching network, i.e.
a low-loss antenna tuner. What is the dynamic gain
range of the receiving load device?
--
73, Cecil http://www.w5dxp.com

Dave,
In a nut-shell, a larger antenna will tend to be more 'receptive'
at lower frequencies. Then you can think about matching the
impedances of the antenna system and receiver.
Larger antennas have the 'problem' of being 'larger', as in where
do you put the thing? Reducing the size of an antenna can be more
practical mechanically, but tends to be less practical electrically
(noise, less 'receptive', etc, etc.). Your 'best' bet would be to
find a reasonable compromise between the two kinds of 'practical'
thingys (mechanical/electrical). Usually easier if you can make it
bigger, sort of.
- 'Doc

(all puns intended, even the ones I didn't intend)

Hey Doc,

Thanks for the input. I overslept for the 1300 UTC broadcast of VOK, but
did pick up the 1500 broadcast. Unfortunately the RF amp offers nothing
over the whip that comes with (and already attached to) my Sony 7600GR
portable. More work to be done. Need to tease out the secrets of impedance
matching, as well as add a boatload of additonal amplification. Damn it's
hard to compete with a successful commercial product. Still, I have at
least reached the level of performance with the RF amp that the preamp in my
7600GR already offered, with the exception of a little additional background
noise.

Hope I didn't discourage Cecil from trying to help. Sorry if I did. I
don't mean to be ignorant, and it is something I am trying to change.

73 and good DX

Dave

wrote in message
ups.com...
Dave,
In a nut-shell, a larger antenna will tend to be more 'receptive'
at lower frequencies. Then you can think about matching the
impedances of the antenna system and receiver.
Larger antennas have the 'problem' of being 'larger', as in where
do you put the thing? Reducing the size of an antenna can be more
practical mechanically, but tends to be less practical electrically
(noise, less 'receptive', etc, etc.). Your 'best' bet would be to
find a reasonable compromise between the two kinds of 'practical'
thingys (mechanical/electrical). Usually easier if you can make it
bigger, sort of.
- 'Doc

(all puns intended, even the ones I didn't intend)

"Dave" wrote in message
...
Hey Doc,

Thanks for the input. I overslept for the 1300 UTC broadcast of VOK, but
did pick up the 1500 broadcast. Unfortunately the RF amp offers nothing
over the whip that comes with (and already attached to) my Sony 7600GR
portable. More work to be done. Need to tease out the secrets of
impedance matching, as well as add a boatload of additonal amplification.
Damn it's

No mater how much amplification you have, if the antenna is not big enough
or the proprgation is not good you will not pick up a station. There is a
limit as to how much you can amplify a signal before the noise floor takes
over. For signals below 15 to 30 mhz or so the noise floor is very high so
not too much amplification can be used to help with the reception.

"Ralph Mowery" wrote in message
...

"Dave" wrote in message
...
Hey Doc,

Thanks for the input. I overslept for the 1300 UTC broadcast of VOK, but
did pick up the 1500 broadcast. Unfortunately the RF amp offers nothing
over the whip that comes with (and already attached to) my Sony 7600GR
portable. More work to be done. Need to tease out the secrets of
impedance matching, as well as add a boatload of additonal amplification.
Damn it's

No mater how much amplification you have, if the antenna is not big enough
or the proprgation is not good you will not pick up a station. There is a
limit as to how much you can amplify a signal before the noise floor takes
over. For signals below 15 to 30 mhz or so the noise floor is very high
so not too much amplification can be used to help with the reception.



Hey Ralph, thanks for coming in. I am wondering though if I can't tune out
some of the noise,and eliminate more with a directional antenna (which I
currently don't have.) Would an IF stage not help me here? Or a second
tuning function, on the output? Just wondering.

Do appreciate your comments. If I'm wrong I'm wrong, I was just thinking
these things might help. No? The signal I am trying to clean up is at 9335
kHz.

Dave

Dave,
Would another 'IF' stage, or filtering, or 'nulling', or whatever you
want to call it, help? Sure. But then you start running into the
'practical' thingy again. It can get sort of complicated deciding
what is 'noise' and what is desired signal. DSP does a lot of that
when told how to do it by the controlling algorithms (or is that 'Al-
Gore-isms'? sorry, I know better, just can't help it). The mainest
problem is the time it takes to do that, it is not instantaneous. And
if you are going to make that controlling algorithm variable, the time
it takes makes things even more time consuming, not to mention
difficult. Keeping in mind that simply making the antenna larger/
longer can do about the same thing at less expense (time/work/$$$),
why not? Easy to do with a recording (sort of), very difficult in
real time. Manually doing all that is almost impossible. How do you
decide what to 'do' before it's too late? There are limits with
today's technology. So, put it off till 'tomorrow', right?
- 'Doc

(all puns intended, even the ones I didn't intend)

Hmmm. Yeah. sigh Point taken. I guess this is just my hobby, and I
really don't have anything better to do (other than housework.) I don't
know what to say. Guess I just have to prove to myself that everything that
can be done has been done, or that it's not worth the effort for the
outcome. sigh again.

I do appreciate all of the feedback, and the patience with my ignorance. I
am trying to make this thing work off of a whip for portability's sake, and
am just not willing to accept defeat yet. May not be much longer though...
It does work great on the external antenna, I just want it to work better
off of the whip.

Thank you, all of you who replied. And thank you, doc, for the final simple
analysis. I don't mean to be stubborn, I just have to try everything to
prove to myself that it is as good as it can be. Sorry. Guess I am
stubborn after all.

The hand-holding is appreciated. Sorry if I frustrated you guys. Thanks
again for your patience.

Dave

wrote in message
oups.com...
Dave,
Would another 'IF' stage, or filtering, or 'nulling', or whatever you
want to call it, help? Sure. But then you start running into the
'practical' thingy again. It can get sort of complicated deciding
what is 'noise' and what is desired signal. DSP does a lot of that
when told how to do it by the controlling algorithms (or is that 'Al-
Gore-isms'? sorry, I know better, just can't help it). The mainest
problem is the time it takes to do that, it is not instantaneous. And
if you are going to make that controlling algorithm variable, the time
it takes makes things even more time consuming, not to mention
difficult. Keeping in mind that simply making the antenna larger/
longer can do about the same thing at less expense (time/work/$$$),
why not? Easy to do with a recording (sort of), very difficult in
real time. Manually doing all that is almost impossible. How do you
decide what to 'do' before it's too late? There are limits with
today's technology. So, put it off till 'tomorrow', right?
- 'Doc

(all puns intended, even the ones I didn't intend)

"Dave" wrote in message
...

Hey Ralph, thanks for coming in. I am wondering though if I can't tune
out some of the noise,and eliminate more with a directional antenna (which
I currently don't have.) Would an IF stage not help me here? Or a second
tuning function, on the output? Just wondering.

Do appreciate your comments. If I'm wrong I'm wrong, I was just thinking
these things might help. No? The signal I am trying to clean up is at
9335 kHz.


Dave you started with a simple whip 40 some inches long. As I mentioned ,
no mater how much amplification you have , the local and not so local noise
will limit the ammount of amplification you can use. All you will amplify
is noise. Lets say you have a noise floor of .3 microvolts and a signal is
picked up from the antenna of .4 microvolts. Your signal will be higher
than the noise and you can hear it to some extent. If the noise is .5
microvolts and you get the same signal , then you will not hear the signal.
If you add an amplifier (one that has no noise of its own , which is
impossiable bu the way) you may get .8 uv of signal, but you will then have
1.0 uv of noise and you will still not hear the signal. The amp may add .1
uv of noise so you then get 1.1 uv of noise and only .8 uv of signal.

You may change the antenna to a tuned loop. Take a couple of sticks about 3
feet long and make an X out of them and wrap a few turns of wire around the
outside of the X so you have a loop about 3 feet square and tune it with a
capacitor to the frequency you wish to hear and it will be somewhat
directional. That may help.

The main thing is that a 3 foot whip in the house is not going to be a very
good antenna for shortwave.

"Ralph Mowery" wrote in message
...

"Dave" wrote in message
...

Hey Ralph, thanks for coming in. I am wondering though if I can't tune
out some of the noise,and eliminate more with a directional antenna
(which I currently don't have.) Would an IF stage not help me here? Or
a second tuning function, on the output? Just wondering.

Do appreciate your comments. If I'm wrong I'm wrong, I was just thinking
these things might help. No? The signal I am trying to clean up is at
9335 kHz.


Dave you started with a simple whip 40 some inches long. As I mentioned ,
no mater how much amplification you have , the local and not so local
noise will limit the ammount of amplification you can use. All you will
amplify is noise. Lets say you have a noise floor of .3 microvolts and a
signal is picked up from the antenna of .4 microvolts. Your signal will
be higher than the noise and you can hear it to some extent. If the noise
is .5 microvolts and you get the same signal , then you will not hear the
signal. If you add an amplifier (one that has no noise of its own , which
is impossiable bu the way) you may get .8 uv of signal, but you will then
have 1.0 uv of noise and you will still not hear the signal. The amp may
add .1 uv of noise so you then get 1.1 uv of noise and only .8 uv of
signal.

You may change the antenna to a tuned loop. Take a couple of sticks about
3 feet long and make an X out of them and wrap a few turns of wire around
the outside of the X so you have a loop about 3 feet square and tune it
with a capacitor to the frequency you wish to hear and it will be somewhat
directional. That may help.

The main thing is that a 3 foot whip in the house is not going to be a
very good antenna for shortwave.



Huuuuhhhh. Okay, I think I am beginning to understand. At least, when you
put it in those terms.

I had thought about using a loop, but for some reason decided to try the
whip first. I guess 'cause that's what I had handy, and I wasn't sure how I
would mount a loop. Until I can figure that out, I am going to try tuning
the output of the RF amplifier the same way I tune the input. If I can work
out the last detail of doing that.

Your words, and numbers, are much appreciated. And your patience.

Thanks, Ralph.

Dave

wrote in message
ups.com...
Dave,
In a nut-shell, a larger antenna will tend to be more 'receptive'
at lower frequencies.

Agree. Years ago I was an avid broadcast band (BCB) DX'er, usually getting
what I wanted late at night. However, when I installed about a 50-foot
dipole wrapped around the inside of my garage, I found an exciting number of
distant stations available during the day. It seems old hat today, but the
experience was valid, I think.