[ADXA] Ameco PT-3 preamp

Fri Jan 24 08:42:45 EST 2025

You will recall (hopefully) that yesterday I said a preamp isn't
intelligent, it will amplify both noise and desired signal. A "broadband"
preamp is quite a bit lower in intelligence, more along the lines of Larry
the Cable Guy. Not only will it amplify noise and desired signal but
everything else floating around the room, the house, the neighborhood, and
the antenna. It may very well have a noisy device as the active component.

73 Joel W5ZN

From: adxa-bounces at mailman.qth.net <adxa-bounces at mailman.qth.net> On Behalf
Of rcurt--- via ADXA
Sent: Thursday, January 23, 2025 8:00 PM
To: w5znjoel at gmail.com; 'BILL KENNAMER' <k5fuv at prodigy.net>; 'Dennis
Schaefer' <dennisw5rz at gmail.com>; 'ADXA' <ADXA at mailman.qth.net>
Subject: Re: [ADXA] Ameco PT-3 preamp

I am not a technical person, and to be honest,  I haven't had much luck
using a preamp on HF. However, after listening to the pennant and finding a
preamp to be necessary, I have become more interested in actually figuring
out how much gain helps, and where the best place to locate the preamp is,
or if location matters at all. 

Coincidentally, before I read this email, I had already downloaded the
schematic to the preamp on the YCCC vertical array and had placed the
"non-junk box" parts in my cart at digi-key or mouser, I've forgotten which.
I did have some questions in my mind about the differences in impedance
matching, not realizing,  due to being weak technically, that the preamp
itself could be useful for impedance matching.  I had put this thought on
hold when I ran across an amazon add for broadband preamps. When I saw the
price, both my brain and wallet came to an agreement on purchasing a pair
for 10 bucks, and they arrived today. I am much less than confident that
they will be of benefit, however in the next few days or so, one of these
will be placed at the pennant feed point, just to see what happens. My
thought is that feedline losses are negligible on 160 and preamp location
will be a non-issue. 

As far as a preamp on the pennant, I run the internal preamp of the 991a on
amp 1. This puts my noise at about S1 on 160. I can't speak to specifics of
gain but I started the project on December 3, and I am becoming more and
more amazed, and pleased with the results. I can now hear stations that I
could not get a peep out of, at this location.  I can't say that I do not
have a unique situation with the noise, that the pennant, and preamp just
happened to be a decent solution. I suppose we really won't know for sure
how unique my situation is until RZ gets his pennant running. 

Always before on 160, and especially after adding 400 watts on transmit. My
TX ability has exceeded my RX. Now it is flipped, my RX is much better than
the TX (in the favored direction of the pennant). BTW I also suffer from
this inequality syndrome when eating chips and dip, or biscuits and gravy.
It may just be a fault in my DNA. 

As far as VHF/UHF, I run a couple of preamps on ota TV. I feel sure this
helps with the losses on the long rg6 run. I also run a mirage external
preamp on the 2-meter Yagi. I feel that without it, most of my msk144
contact and all of my few EME contacts would not have been possible.
However, when vhf is noisy, I have no other alternative but to sit here and
contemplate taking up golf. 

Somewhere in the unknown abyss of items is a kit preamp I built back in the
90's. It could have been one of those Ramsey kits, I don't remember.
Hopefully it will make its way into my hand, as it does randomly from time
to time, before it departs back into the abyss to not be seen again for
years. I would like to give using it another shot, as my past ideas of using
a preamp have been changed, and I know now that a preamp used in the right
situation is absolutely invaluable.

Thanks to all for taking the time to email your thoughts and experiences. I
really enjoy reading and learning from them. 

Randy/W5ZJ 

  _____  

From: adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net>
<adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net> > on
behalf of w5znjoel at gmail.com <mailto:w5znjoel at gmail.com>
<w5znjoel at gmail.com <mailto:w5znjoel at gmail.com> >
Sent: Thursday, January 23, 2025 2:18 AM
To: 'BILL KENNAMER' <k5fuv at prodigy.net <mailto:k5fuv at prodigy.net> >; 'Dennis
Schaefer' <dennisw5rz at gmail.com <mailto:dennisw5rz at gmail.com> >; 'ADXA'
<ADXA at mailman.qth.net <mailto:ADXA at mailman.qth.net> >
Subject: Re: [ADXA] Ameco PT-3 preamp 

ADXA Folks,

Second to antennas, a preamp is my most favorite topic to discuss and Bill
FUV states a very valid point we must all pay attention to. I have no direct
experience with the PT-3 but I do have considerable experience with preamps
in general.

A question I'm asked frequently is "Do I need a preamp?" to which I always
reply "I don't know, do you?" That's not meant to be a derogatory response
but a valiant attempt to get the person to learn what a preamp does, and
does not, do and determine whether one is appropriate for your specific
situation.

A preamp is simply that, an amplifier prior to the receiver that will
amplify noise along with the desired signal. You can add high pass, low
pass, and bandpass filters that will help reduce unwanted out-of-band
signals being amplified but remember noise is generic, its just like Santa
Claus - IT'S EVERWHERE!! The preamp isn't intelligent, all it knows to do is
AMPLIFY so it does so equally to everything! Thus the need to have a preamp
with a low noise figure. A preamp with a noise figure of 0.5 dB and 10 dB of
gain is exponentially more effective than a preamp with a noise figure of 2
dB and 25 dB gain. "Mo gain is not necessarily mo better!" I won't go into
the math but can provide it if you want to fry your brain.

BUT WAIT!!!!! We're talking 1.8 MHz so you really can't achieve a low noise
figure in the real world, like you would in the VHF and above region,
because atmospheric and other noise limits the effective noise figure you
can achieve at 1.8 or 3.5 MHz. I believe Dennis RZ has proven this when he
notes the PT-3 seems to do better as he advances higher in frequency.

As I noted in my paper on vertical array comparison I don't use a preamp on
my RX antennas however, you WILL need one if you're using a loop type RX
antenna because that type of antenna's gain is low. Yes, I know "gain" is
not our objective for a low band RX antenna but there is a point of
diminished return. The only way you can determine if an improvement is
realized with a preamp is to do exactly what Dennis RZ is doing - try and
see what the result is. If it is not what you expected. Investigate why and
try something else. I don't recall if the PT3 has a variable gain control or
if it is fixed. There was one similar preamp design that provided an
adjustment to vary the gain. If so, give that a try.

Randy ZJ is using the same approach in his evolution with loop antennas. Try
it, document the result, try something else, document the result, then
compare!

These are all great topics to discuss, and projects to work on, to get us
all ready to GET IN THERE !!!!!!

73 Joel W5ZN

From: adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net>
<adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net> > On
Behalf Of BILL KENNAMER
Sent: Wednesday, January 22, 2025 10:52 PM
To: Dennis Schaefer <dennisw5rz at gmail.com <mailto:dennisw5rz at gmail.com> >;
ADXA <ADXA at mailman.qth.net <mailto:ADXA at mailman.qth.net> >
Subject: Re: [ADXA] Ameco PT-3 preamp

The more gain it has, the worse the s/n ratio. It amplifies noise too.
Probably 10-20 db is enough.

FUV

Sent from AT <https://more.att.com/currently/imap> &T Yahoo Mail for iPad

On Wednesday, January 22, 2025, 9:52 PM, Dennis Schaefer
<dennisw5rz at gmail.com <mailto:dennisw5rz at gmail.com> > wrote:

I bought Lenny's PT-3 preamp years ago but recently connected it  for the
first time.   I thought even though it wouldn't be at the antenna feedpoint,
it might be helpful with low band receive antennas with low output.  

I tried it and it has gain, but it doesn't really seem to help the S/N
ratio.  I haven't found a lot of online info yet, but it seems that it is
mainly helpful on higher bands.  It probably would have helpful on one of my
old tube rigs that lost sensitivity on 10M.  

I just wondered if anyone else had any experience or tips for this piece of
equipment, especially for use on 160 or 80 meters.

73,

Dennis/RZ

______________________________________________________________
ADXA mailing list
Home: http://mailman.qth.net/mailman/listinfo/adxa
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:ADXA at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/adxa/attachments/20250124/8755a4d2/attachment-0001.html>