On 4/8/2014 4:34 AM, Geoffrey S. Mendelson wrote:
I have a copy of the book "Practical Wire Antennas" by Heyes (the first
edition). In it is a schematic for a low noise broadband preamplifier
for loops.

This version uses the BSX20 transistor which at the time the book was
written was far more available in the UK than the 2N5179 used by the
original Hayward design.

The book mentions that it was first published in the ARRL Antenna
Handbook, I can not find it in my copy.

These days it is much cheaper and easier to order 2N5179 transistors
from China on eBay (and probably cheaper to order 10 and pick the best)
than it is for me to order a BSX20.

However without the original schematic or construction article, I am
taking it on faith that it will work with no circuit changes, something
I doubt.

A copy of the schematic and accompanying text would be appreciated.
References to where it appeared or links to pages describing it would be
even better.


The original circuit I was looking at contained 1 transistor, 4 diodes,
6 1/4 watt resistors and 4 disk capacitors. The coil could be wound from
hookup wire on a hunk of ferrite rod, which I have many of.

It's fairly "bulletproof", so high voltages from static, lightening
or nearby transmitters (all three here) won't burn it out like an MMIC.

It's a simple design so that I can build it myself. :-)

TIA,

Geoff.

You might be interested in this amp also.
http://w7iuv.com/
Find W7IUV preamp on left side and click.
Mikek

On Sat, 12 Apr 2014 19:13:10 -0500, amdx wrote:

You might be interested in this amp also.
http://w7iuv.com/
Find W7IUV preamp on left side and click.
Mikek

http://w7iuv.com/preamp60/preamp_r60.pdf

I can't take it any longer...

It's a nice construction article. Too bad it's missing test results
and graphs for the key parameters necessary for a proper HF RF
amplifier. The article correctly identifies the major problem, which
is IP3 or 3rd order intercept point. With all the RF floating around
on HF, overload capability is the key parameter. 2nd most important
is filtering, which helps with overload problems, but also reduces
noise which might mix with some out of band signal, and land in your
bandpass.

Note that the author use 2N3866 and 2N5109 xsistors. These are power
devices, not low noise devices. The clue is the heat sink on the
cans. If you want to handle 1/2 watt of power in your receiver input
stage, and remain linear, you'll need to smoke about 1 watt (or more)
of power in the RF xsistor.

The problems are similar for WWVB loops. If you do a survey of RX
amps for 60 KHz WWVB receivers, you'll find a few that have power
dissipating front ends. You don't need to smoke much power if you're
only going to listen to the local time signal. The very high Q of the
loop (loaded Q=100) will take out most of the out of band signals.
However, all the other time signal transmissions will be within the
bandpass of the loop. If you're trying to listen to a distant time
signal, but you the local transmitter is really loud, you're going to
have a problem. So, the better receivers burn the necessary power in
the front end to handle the potential overload, while the cheaper
units just hope for the best with lower power front ends.
(Incidentally, my 100 KHz LORAN front ends smoked dissipated about 1/2
watt and required a heat sink).

The title of this thread "Hayward design broadband low noise preamp
for loops" is wrong because the last thing you need on a 60 KHz loop
or an HF receiver is a low noise preamp. The atmospheric noise on the
lower HF frequencies is so high, that a low noise amplifier is wasted.
All that the added gain does is decrease the dynamic range. Many HF
receivers feed the first mixer directly from the antenna (after a low
pass filter) with no RF amplifier in sight. It's not needed.

Summary:
- If you're doing 60 KHz with a loop, you don't need a low noise
front end and you might need a high IP3 amp.
- If you're doing 60 KHz with a wire antenna, you don't need a
low noise front end and you will need a high IP3 amp or a very
good front end filter.
- If you're doing HF (2-30 MHz), you don't need a low noise front
end, and you certainly are going to need a high IP3 amp.
- If you're doing VHF/UHF/microwave, you'll need a low noise front
end, and for repeater use, a high IP3 amp.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
Thanks Jeff, (and the others that responded)
Summary:
- If you're doing 60 KHz with a loop, you don't need a low noise
front end and you might need a high IP3 amp.

Not 60hZ, nothing here at that frequency, nor 50kHz EU signals.


- If you're doing HF (2-30 MHz), you don't need a low noise front
end, and you certainly are going to need a high IP3 amp.

To be exact, I am looking for MW broadcast using the loop.
and lower HF bands (80m/40m/6mHz SWBC) using a short antenna, similar to
a PA0RDT type (in only that it is a short wire/pole connected to an
amp).

Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379

On Sun, 13 Apr 2014 09:54:23 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

- If you're doing HF (2-30 MHz), you don't need a low noise front
end, and you certainly are going to need a high IP3 amp.

To be exact, I am looking for MW broadcast using the loop.
and lower HF bands (80m/40m/6mHz SWBC) using a short antenna, similar to
a PA0RDT type (in only that it is a short wire/pole connected to an
amp).

The PA0RDT design is a "mini-whip" not a loop.
http://dl1dbc.net/SAQ/miniwhip.html
Very different. Could you be more specific as to what you're trying
to accomplish, and what you have to work with?

Meanwhile, I suggest grounded base. (My thanks to MikeK a.k.a. amdx
for the references). I've built similar amps but never realized where
they originated. The big advantage of grounded base is that it's very
very very very stable.
http://www.thegleam.com/ke5fx/norton/norton_rohde_lankford.pdf
http://www.thegleam.com/ke5fx/norton/lankford.pdf
http://www.google.com/patents/US3891934?dq=3,891,934
Details. Note that the design was not made for an HF receiver amp:
http://www.cliftonlaboratories.com/norton_amplifier.htm
11dB gain. +50dBm IP3. 100mw out at 1dB gain compression.
Wheeeee... You could probably use it as a QRP transmitter.

More later. I'm rather busy today.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558