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: [email protected] <[email protected]> On Behalf Of rcurt--- via ADXA
Sent: Thursday, January 23, 2025 8:00 PM
To: [email protected]; 'BILL KENNAMER' <[email protected]>; 'Dennis Schaefer' <[email protected]>; 'ADXA' <[email protected]>
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: [email protected] <[email protected]> on behalf of [email protected] <[email protected]>
Sent: Thursday, January 23, 2025 2:18 AM
To: 'BILL KENNAMER' <[email protected]>; 'Dennis Schaefer' <[email protected]>; 'ADXA' <[email protected]>
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: [email protected] <[email protected]> On Behalf Of BILL KENNAMER
Sent: Wednesday, January 22, 2025 10:52 PM
To: Dennis Schaefer <[email protected]>; ADXA <[email protected]>
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&T Yahoo Mail for iPad
On Wednesday, January 22, 2025, 9:52 PM, Dennis Schaefer <[email protected]> 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
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