Radios4you has some of these up on eBay. Normally, I don't buy from eBay,
but this was a good deal. He has them advertised as the boards for the
HF-250 but when I e-mailed Lowe UK, Tony told me that there was only one
board made, the W225 preamp board. I think what fooled Frank and myself at
first was that the component layout is slightly different from the older
iteration.
I compared this board to the schematic in my HF-225 service manual, and with
the exception of the additional 22uF cap they are electrically the same.
I installed it my my HF-225 last night and it works like a champ.

Pete

"Pete KE9OA" wrote in message
...
Radios4you has some of these up on eBay. Normally, I don't buy from eBay,
but this was a good deal. He has them advertised as the boards for the
HF-250 but when I e-mailed Lowe UK, Tony told me that there was only one
board made, the W225 preamp board. I think what fooled Frank and myself at
first was that the component layout is slightly different from the older
iteration.
I compared this board to the schematic in my HF-225 service manual, and
with the exception of the additional 22uF cap they are electrically the
same.
I installed it my my HF-225 last night and it works like a champ.

Pete
Hi Pete- excellent find. I saw them too.
With all the discussion on the group about active antennas, this would be a
good opportunity for the homebrewers out there to build up an active antenna
with these Hi Z in preamps as a basis.

Dale W4OP

On Sat, 11 Feb 2006 13:53:16 GMT, "Dale Parfitt"
wrote:


"Pete KE9OA" wrote in message
...
Radios4you has some of these up on eBay. Normally, I don't buy from eBay,
but this was a good deal. He has them advertised as the boards for the
HF-250 but when I e-mailed Lowe UK, Tony told me that there was only one
board made, the W225 preamp board. I think what fooled Frank and myself at
first was that the component layout is slightly different from the older
iteration.
I compared this board to the schematic in my HF-225 service manual, and
with the exception of the additional 22uF cap they are electrically the
same.
I installed it my my HF-225 last night and it works like a champ.

Pete
Hi Pete- excellent find. I saw them too.
With all the discussion on the group about active antennas, this would be a
good opportunity for the homebrewers out there to build up an active antenna
with these Hi Z in preamps as a basis.

Dale W4OP


The active device is not a preamp. It is an impedance converter.

The active device is not a preamp. It is an impedance converter.

I thought that was clear from my post when I said Hi Z in.
And that is EXACTLY what is required in an "active antenna"
Although I do not own that particular Lowe board, my Lowe HF-150 "whip
preamp" has gain in addition to Z conversion, so I fail to see where the
term preamp does not apply.
Dale W4OP

It seems to me that to keep the input referred noise as small as
possible, you would want gain.

Dale Parfitt wrote:

The active device is not a preamp. It is an impedance converter.

I thought that was clear from my post when I said Hi Z in.
And that is EXACTLY what is required in an "active antenna"
Although I do not own that particular Lowe board, my Lowe HF-150 "whip
preamp" has gain in addition to Z conversion, so I fail to see where the
term preamp does not apply.
Dale W4OP

On Sat, 11 Feb 2006 18:36:47 GMT, "Dale Parfitt"
wrote:



The active device is not a preamp. It is an impedance converter.

I thought that was clear from my post when I said Hi Z in.
And that is EXACTLY what is required in an "active antenna"
Although I do not own that particular Lowe board, my Lowe HF-150 "whip
preamp" has gain in addition to Z conversion, so I fail to see where the
term preamp does not apply.
Dale W4OP

No need to be defensive. We're all friends here. We're both correct.
I was hoping to get the less experienced among us to understand a
little better.

A short (i.e. 1/4 wavelength) antenna is always high impedance.

p.2 http://www.mfjenterprises.com/man/pdf/MFJ-1024.pdf

On 11 Feb 2006 10:51:04 -0800, wrote:

It seems to me that to keep the input referred noise as small as
possible, you would want gain.

An amplifier can't tell ''noise'' from ''desired''. S:N is unchanged
by an amplifier.

Note specifically I said input referred noise.

If you don't put gain in the preamplifier (i.e. you do the so-called
impedance only function), then the AGC of the radio will amplify the
noise of the preamp. Since there is no gain in the preamp, you have
the combination of the noise from the preamp and the amplifier (i.e.
AGC) of the radio. If the preamp has some gain, then the AGC will do
less amplification, thus the noise will be dominated by the preamp.




David wrote:
On 11 Feb 2006 10:51:04 -0800, wrote:

It seems to me that to keep the input referred noise as small as
possible, you would want gain.

An amplifier can't tell ''noise'' from ''desired''. S:N is unchanged
by an amplifier.

David - Thank You for the Leason ~ RHF

On 11 Feb 2006 16:54:54 -0800, wrote:

Note specifically I said input referred noise.

If you don't put gain in the preamplifier (i.e. you do the so-called
impedance only function), then the AGC of the radio will amplify the
noise of the preamp. Since there is no gain in the preamp, you have
the combination of the noise from the preamp and the amplifier (i.e.
AGC) of the radio. If the preamp has some gain, then the AGC will do
less amplification, thus the noise will be dominated by the preamp.



IP3