Is there a fairly quick answer to the question of what is involved with
matching an RF amplifier to a whip antenna? I have built an active, tunable
antenna to assist my shortwave receiver, and it works wonderfully on the
110' random-wire antenna up on the roof, but only picks up the strong
stations with the whip. Those that it picks up come in great, but there are
others that it is able to detect but not lock on to and make intelligable,
IE BBC Africa, 7160 kHz around 0400/0500 UTC (and I am on the Gulf Coast of
Texas).

Just wondering,

Thanks for any feedback or input.

Dave

On Sat, 10 Nov 2007 01:04:00 -0600, "Dave" wrote:

Is there a fairly quick answer to the question of what is involved with
matching an RF amplifier to a whip antenna? I have built an active, tunable
antenna to assist my shortwave receiver, and it works wonderfully on the
110' random-wire antenna up on the roof, but only picks up the strong
stations with the whip. Those that it picks up come in great, but there are
others that it is able to detect but not lock on to and make intelligable,
IE BBC Africa, 7160 kHz around 0400/0500 UTC (and I am on the Gulf Coast of
Texas).

Just wondering,

Thanks for any feedback or input.

Dave


is the whip some sort of reduced size antenna?

The smaller an antenna is, the worse is the performance.

w.

"Helmut Wabnig" hwabnig@ .- --- -. DOT .- t wrote in message
...
On Sat, 10 Nov 2007 01:04:00 -0600, "Dave" wrote:

Is there a fairly quick answer to the question of what is involved with
matching an RF amplifier to a whip antenna? I have built an active,
tunable
antenna to assist my shortwave receiver, and it works wonderfully on the
110' random-wire antenna up on the roof, but only picks up the strong
stations with the whip. Those that it picks up come in great, but there
are
others that it is able to detect but not lock on to and make intelligable,
IE BBC Africa, 7160 kHz around 0400/0500 UTC (and I am on the Gulf Coast
of
Texas).

Just wondering,

Thanks for any feedback or input.

Dave


is the whip some sort of reduced size antenna?

The smaller an antenna is, the worse is the performance.

w.

It's a 43 inch collapsable antenna (7 segments.) Maybe I just need more
amplification...

Thanks,

Dave

On Sat, 10 Nov 2007 01:58:28 -0600, Dave wrote:
"Helmut Wabnig" hwabnig@ .- --- -. DOT .- t wrote:
On Sat, 10 Nov 2007 01:04:00 -0600, "Dave" wrote:

Is there a fairly quick answer to the question of what is involved with
matching an RF amplifier to a whip antenna? I have built an active, tunable
antenna to assist my shortwave receiver, and it works wonderfully on the
110' random-wire antenna up on the roof, but only picks up the strong
stations with the whip. Those that it picks up come in great, but there are
others that it is able to detect but not lock on to and make intelligable,
IE BBC Africa, 7160 kHz around 0400/0500 UTC (and I am on the Gulf Coast
of Texas).

is the whip some sort of reduced size antenna?

The smaller an antenna is, the worse is the performance.

It's a 43 inch collapsable antenna (7 segments.) Maybe I just need more
amplification...

No. You need more antenna.

If you add amplification to a marginally performing antenna, you will
also amplify all the nearby interference: power line noise, dimmer
lights, electrical motors, poorly shielded TVs, etc. usw.

Sure, the desired signal(s) may come up in strength by adding more
amplification to a poor antenna, but everything you _don't_ want to hear
will be stronger, too.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

On Sat, 10 Nov 2007 01:58:28 -0600, "Dave" wrote:

It's a 43 inch collapsable antenna (7 segments.) Maybe I just need more
amplification...

Hi Dave,

You need more antenna...
... but not much more.

When I was in Africa with a Radio Shack $40 SW receiver, the whip was
a dummy load that let me hear the internal microprocessor clock that
was driving the digital display. I attached 20 feet of wire-wrap wire
to the whip, threw the wire end (weighted with a Rand) up onto the
reed roof of the lodge I was in and I got more signals than I could
handle with only about 4 meters of height. The bands from 2.3 MHz to
16 MHz played all day/night long.

73's
Richard Clark, KB7QHC

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

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

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