HF signal amp with homebrew loop

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corbintechboy

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Hello,

I have setup an loop here in my home. I had a problem with noise and have strung wire around my bathroom in my room to create a loop. The noise has disappeared and it works great (things that at one time were buried in noise now have an easy copy, noise floor is low as well).

I am going to get into SDR. I have my R75 and its nice with the lower noise floor, of course with the lower noise floor comes a lower signal as well. I would like to buy some sort of variable amplifier to boost the signals. Since this setup has a nice low noise, boosting the signal should keep the same low noise while boosting the signal.

I want something like this, is this however something I need? I notice most loops you buy are amplified. I figure the reason is the lower signal.

Any suggestions for a unit?

Thanks in advance.
 

k9rzz

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What frequency range are we talking about? More info on the loop? BIg? Small?

You will have some noise with an amplifier because they make everything louder, not just what YOU want louder.

Which one is best? Got me. +:^] But more info on your loop and frequency range would help.
 

corbintechboy

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My loop goes around the top of a room. It might be a 12x12 square.

What I will listen to is below 15Mhz. I might tune up from time to time, but not that likely. I do some broadcast listening and listen to some two way comms, some utility decoding as well. My uses are broad.

Thanks for the reply.
 

ka3jjz

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I would use the amp that's built into the R75 first as a test, to see if amplification really buys you anything besides a higher noise level.

If I were buying an amp, I would make sure that the gain can be varied. This is an obvious need when you realize that the higher noise floors are found on the lower HF bands. You want to be able to cut the gain down in such cases. Too much gain, and more noise is the likely result.

Unfortunately they've been discontinued, but the Palomar P305 is excellent in this regard. I have one in storage right now (the switches aren't in the best of shape...) but when I had my other shack it was indispensible. The variable gain and selectivity were outstanding. If you weren't tuned properly, you heard nothing - nice and tight. And you could even select between 2 antennas.

You have to learn how to ride your AGC and volume control to be able to determine just how much is too much. Basically you would disable your AGC (if you can) - the volume is going to jump up considerably, and you would need to ride your volume and RF gain, in concert with the preamp in order to determine your optimum settings. This takes time and practice to learn, frankly, because every receive condition is different for a different environment.

Remember, easy on the gain! Mike
 

corbintechboy

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Thanks for the reply.

I have messed with the preamp on the R75. What I find is on some signals (tough signals) preamp one can help, preamp 2 can help more under certain conditions.

My setup, now, will pick up signals with nothing showing on the S-meter. This is nice as it represents a very good noise floor (and I get this throughout where I listen other then spikes on the turns from display noise).

I will give an example of a before the loop (noise aside). I listen to 1100 from Cleveland often. Using my old antenna I would receive the signal at +20 on the meter. Got it playing now and sitting at S-6 with modulation jumps to S-8. Clean signal indeed (some fading (ecss time :D). Now on ecss and jumping from S-1 to S-6. So the signal is not as strong as it was on a wire, although lower noise but with the lower signal. Nice in one area not so nice in another? Maybe I am thinking it wrong.

So, I wonder if I am missing stations due to the lower signal in general and if a nice quite amp would be ideal or is my living in the country away from people paying me in nice ways I am not used to? My R75 has never picked up a signal with no S-meter reading in its life.
 
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ridgescan

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So, I wonder if I am missing stations due to the lower signal in general and if a nice quite amp would be ideal or is my living in the country away from people paying me in nice ways I am not used to? My R75 has never picked up a signal with no S-meter reading in its life.
More likely, your loop, the way it's positioned, is nulling a nearby noise source-so I say yeah, an amp might work well with the null you got going there. MFJ makes some decent ones.
I'll start you with some fleabay picks
MFJ 1020A RECEIVER PRESELECTOR ACTIVE ANTENNA PREAMP | eBay
 

corbintechboy

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Thanks for the reply.

I have done some research into your suggestion and I think I am gonna go with this:

Ameco PT3 Preamp

It just seems the build quality is better then MFJ. What I will do with the SDR is just run that in a bypass mode to get the broad display on the spectrum. If I find something I want to hear and it is weak, fire it up tune and get it blasting through my bose wave radio (I use as my computer speaker, should make the SDR sound nice).

Thanks for the reply, I believe this may be what the doctor ordered :D.
 

ka3jjz

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Never overuse the gain control on a preamp. Go for just enough gain to get the signal out of the noise, and no more. Chances are that if you crank that preamp on full all the time, you will enhance noise as well as signal.

This takes practice - it all depends on band conditions and how the radio will react to the increased signal level. Listen as you adjust - at some point you are going to notice where the noise and signal tend to get amplified at a similar rate.

Remember, like I said earlier, easy on the gain! Mike
 

ridgescan

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Looks like a good one there RT. You have a good plan there. I run my r75 and my bc785d through my old Sony str-d790 A/V unit with Bostons for some well-tailored voice-I bet that Wave radio is good for this application. Let us in on how effective your Ameco is-I for one might be interested in getting one too.
 

corbintechboy

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Never overuse the gain control on a preamp. Go for just enough gain to get the signal out of the noise, and no more. Chances are that if you crank that preamp on full all the time, you will enhance noise as well as signal.

This takes practice - it all depends on band conditions and how the radio will react to the increased signal level. Listen as you adjust - at some point you are going to notice where the noise and signal tend to get amplified at a similar rate.

Remember, like I said earlier, easy on the gain! Mike
Thanks for that.

My couple years with the R75 (and the host of other good radios I have owned) have showed me the gold that is in the fine tuning of the gain. It works wonders on the R75 to reduce noise (not so much now, I have no noise issues). Without AGC and the R75 it works well as well. I have used it in that manner a couple times as well.

Looks like a good one there RT. You have a good plan there. I run my r75 and my bc785d through my old Sony str-d790 A/V unit with Bostons for some well-tailored voice-I bet that Wave radio is good for this application. Let us in on how effective your Ameco is-I for one might be interested in getting one too.
No problem Ridge.

I will let you know how it works out. After all, you convinced me to get the R75 (I am corbintechboy, got hacked and had to recreate my online me. Long story).

Thanks :D.
 

zz0468

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I did quite a bit of research on loop antennas and preamplifiers for low HF, MF, and LF many years ago. I found that if you can create a tuned loop, the antenna will deliver more signal power to the receiver than an untuned loop, and could make any sort of preamp unnecessary.

Tuning a single turn loop like that is not difficult.

If you decide to continue with an untuned loop, then a preamp that's specifically designed with a low noise figure (<2db) at the frequencies of interest will give long wire received signal levels, and maintain the low noise and directional null capabilities of a loop.
 

corbintechboy

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I did quite a bit of research on loop antennas and preamplifiers for low HF, MF, and LF many years ago. I found that if you can create a tuned loop, the antenna will deliver more signal power to the receiver than an untuned loop, and could make any sort of preamp unnecessary.

Tuning a single turn loop like that is not difficult.

If you decide to continue with an untuned loop, then a preamp that's specifically designed with a low noise figure (<2db) at the frequencies of interest will give long wire received signal levels, and maintain the low noise and directional null capabilities of a loop.
I'm actually trying to figure out the best course of action in regard to the antenna system.

This loop is working nice with the low noise. The reason I did this is I had a wire around the room it is in but have a noisy outlet in there for some reason. the way the loop is situated along the ceiling line it nulls the noise nicely. But there is no steering the loop, so it serves a single purpose and anything else that gets nulled is a casualty.

I have about six acres in the country. The problem I face (I have grounds in place) is no trees and still this fear of creating a lightening rod with an outdoor antenna. It bothers me because my property would allow for about any configuration I might need, but I fear what might get destroyed or how much lightening arreststores (sp?) might cost me in the long run. What I have works, not really ideal.
 

k9rzz

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Nothing wrong with a healthy respect for electricity. Don't let it paralyze you though.

Yes, L O N G wires do pick up a lot of energy ... that's why we put them up!
 

SpectreOZ

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A multitude of antennas will provide differing solutions to your listening requirements for example magnetic loops are great for RX and inherently have a low noise floor as well, one of these outside could be used to augment an outdoor longwire and anything else you may have installed, I regularly chop and change between a random longwire, a fixed folded dipole loop (T2FD) and a small vertical depending on conditions and interference.

RadioTuner your horizontal loop sounds interesting... perhaps it would make another candidate to my listening arsenal? :D
 

corbintechboy

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A multitude of antennas will provide differing solutions to your listening requirements for example magnetic loops are great for RX and inherently have a low noise floor as well, one of these outside could be used to augment an outdoor longwire and anything else you may have installed, I regularly chop and change between a random longwire, a fixed folded dipole loop (T2FD) and a small vertical depending on conditions and interference.

RadioTuner your horizontal loop sounds interesting... perhaps it would make another candidate to my listening arsenal? :D

Last night I decided to tinker. I strung outside about 300 feet of wire. Fed that into the radio (balun of course) and compared the two antennas. Here's what I found:

The longwire gives an illusion of picking up more because it also has a higher gain(?) then the loop. More natural noise is introduced into the signal with the wire. It was indeed slightly better on MW with the wire, but I have the excellent Quantum loop for that so not imprtant to me.

The loop I have in the house has a lot less natural noise and has a waay better S/N ratio. I actually like the loop much better.

I live in the center of what could be a hilly field. I am perched on a slight hill. My home is a 2006 double wide with wood framing and vinyl siding. Being where I am, I am not feeling like putting the antenna outside is gonna all the sudden give me some sort of better result.

My boss has giving me a spending limit as she often does :D. So I have decided that for right now I am going to use my current setup and play with loops and get the amp above.

I don't want to be faced with the good antenna or radio issue with her. We have kids and she does not want the yard cluttered with my wires (lol).

So I will get the radio and probably end up with something like a Welbrook or a Pixel loop and some sort of sloper down the line. Been wanting an SDR for so long (I have dongles but thats it (well softrock)).

So I think this is my plan.
 

k9rzz

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Very good, but you can't evaluate an antenna over night. (and it's not just me that say's that)

Leave that 300 footer up if you can, give it a chance to strut it's stuff.
 
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