Recieve Amp/PreAmp

[BrettL]

Is a receive amp all that necessary when It just boosts the unwanted crappy signals too?

I was at a friends the other night and got to talk 80, 75, 40 meters. This was my first QSO ever on a Ham's radio. I think it was a Kenwood TS-120S. The receive was ok I guess but I cant compare to anything else because I have never been around another HF transceiver in operation. It also had a top mounted speaker which was awful.

There was too much static riding peoples signals even at 5 over 9 or higher. I know there are many variables to consider with his antennas and setup . It was dark and I never saw the wires.

So I have been reading about some high entry level transceivers and how they have better receive.

So my question is if I add a pre amp to a transceiver that had a clearer receive would it boost the clarity of the signals or does it also depend on the type of pre amp it is?

Is there a pre-amp to help eliminate unwanted hash to help the receiver or does it all start with the radio itself?

Can anyone elaborate so I can understand?

 

[zz0468]

Proper use of a preamp is quite a complex process. First consideration is noise figure. It MUST have a lower noise figure than the receiver that follows it, or it won't actually help with weak signal reception. It'll make the s-meter deflect more, but that's almost completely meaningless.

In HF, another consideration is external noise. If a specific antenna is receiving some specific amount of noise, and a desired signal is arriving below that noise floor, a preamp will only cause the s-meter too deflect more, but won't pull signals out of the noise.

In HF, signals are usually plenty strong enough, the problem is usually a need to reduce the noise.

Preamps don't do that.

A good application for a preamp on HF would be with a magnetic loop or beverage antenna, something that is inherently less noisy.

Active noise reduction takes a completely different set of tools.

 

[AK9R]

A good "rule of thumb" is to remember that pre-amps amplify noise as well as signal. If the antenna is a noisy design (on HF, vertical antennas are usually noisier than horizontal antennas which are noisier than loops) or if the local environment is noisy (power lines, consumer electronic devices, electrical machinery) or if the band conditions are noisy (lower HF bands are usually noisier in summer than in winter), the pre-amp may make the noise heard at the receiver appear to be worse than without the pre-amp. I learned a long time ago that when the band conditions are noisy, you have to turn down the RF gain.

The Kenwood TS-120S is an older radio with limited features. More modern radios have DSP noise reduction and adjustable IF bandwidths to help fight noise and interference problems.

 

[BrettL]

So when I do get me a hf rig do I need to look for the features that make it less noisy on receive and get a antenna that has less noise or would there be a loss of gain in a antenna to achieve a lower noise level?

Any good articles to read on anything like this?

Also remember I am new and I may not know how to ask the question correctly. So please bare with me. I have 10,000 more questions.

 

[AK9R]

Most modern HF radios above the lowest entry level have some form of DSP noise reduction in the IF stage of the radio. How well it works is often subjective. But, don't expect something for nothing. If the bands are noisy, DSP can help, but it won't make it like listening to FM.

 

[prcguy]

HF reception through about 20m is governed mostly by signal to noise ratio and any radio connected to a fairly large antenna will have a signal to noise ratio that will not be improved by adding a preamp. If you are starving a receiver for signal as in the examples zz0468 gave or are trying to use a clip lead as an antenna then a preamp may improve the SNR and make reception better.

Above 20m or so like 10m where there is less atmospheric noise and when conditions are quiet like no skip, a preamp can improve reception and possibly allow you to hear weak distant stations a little better. If conditions are good on 10m then the atmospheric noise level is usually higher and will set the SNR at a point where a preamp will probably not benefit.

Another thing that can happen when you add a preamp is many if not most broad band preamps will easily overload on a big antenna and create internal Inter Modulation Distortion, or lots of ghost signals across the band which can appear like noise because there are so many of them. Basically your noise floor becomes higher than what just the gain of the preamp is and your SNR is actually reduced. Cramming more signal into a receiver can also cause the receiver to generate internal IMD in its front end preamp (if it has one) or mixer or other stages.

Generally the more you spend on a radio the better receiver it has and it may be less prone to IMD and other problems, plus you get more features to help eliminate noise. If you look at the receivers in the following list, generally the ones higher on the list will have quieter receivers and will be more pleasant to use because the properties that give them high marks on the list also go a long way towards reducing internal IMD, LO phase noise and other things that make them noisy.

Receiver Test Data

I have several lower cost radios now like an Icom 706MKIIG and Yaesu FT-857, which I can't use for any long period of time in the house because I've been spoiled by much higher performing and quieter receivers like the Elecraft K3 and KX3, Tentec Omni VII and Eagle plus some late model Harris HF stuff. Other radios I've used in the past like the Yaesu FT-757 were just awful and full of noise. Just a few weeks ago I used a friends Kenwood TS-690S which I had owned years ago and thought was pretty good in the 1990s but now I just can't use it for very long without cringing.

I recommend trying all your friends radios and as many as possible to see what you like and don't like, then see what is the best radio that fits your budget. I'll warn you that playing with a really high end receiver might lean you towards the more expensive stuff and once you hear a really good receiver its hard to go backwards.
prcguy

 

[wyShack]

For the most part the limiting factor on HF (or shortwave) is not signal strength but noise. When selecting a receiver (or transceiver), the sensitivity is a minor item. features such as narrow filters, noise blanker, DSP (digital signal processing) are more useful than more sensitivity. Proper grounding, antenna (and location of) and many other factors come into play-not just the radio. The typical home today includes many pieces of electronics which unintentionally radiate radio 'noise'. remember a receiver is part of a system and plan accordingly.

There are several threads here on RR and many other sites that discuss the issue of electrical noise ( static, EMI and other terms). most of the solutions to 'weak' signal work on HF involve more than the receiver. keep reading and good luck. Also remember that noise is something we live with-full quieting is not needed to communicate and one of the problems may be your own expectations.

73

 

[jim202]

You might want to consider using a grounded antenna like a folded dipole or a delta loop. These type antennas will reduce the static buildup in antennas. Especially rain and snow static.

If your ever at a place that has both an open dipole and some sort of loop antenna like a folded dipole, switch back and forth between them. You will be truly surprised at the big difference.

 

[BrettL]

I read some articles about how you can get static from wind and tiny particles blowing across your antenna, distant storms no where near you, proper grounds and among other things that create static and noise, I think it came from the 2006 ARRL radio handbook I bought that year. I was still operating CB at the time and just wanted the book because it interested me at the time. I actually got it back out the other night and started reading it again. I have been reading so much lately that I'm forgetting what I read the first time. Too much too quick.

That SE- 3 was a major improvement. I may can get me one after I get me a rig first. If loops are quieter then that's what I probably will go with. I still got to have my dbd gain too. The only thing is that where I will put up my wires they will be close to the ground on one end and high in the air on the other because my yard takes a drop off in on the back side. I can make them perfectly horizontal to help with the noise but I do know that when you DX the signal does get flip-flopped and scattered off everything causing it get into the receiving antennas at a different angle which can cause a signal loss of some sort.

I have seen several wires put up high on one end and droop towards the ground on the other. To me that's a 45 degree angle. I would not like that, but then again I did say that the signal does get scattered around up there and down here when its skipping and hopping around.

I forget what meter my ham friend said he was running one day and his other friend was just a few miles away running some good watts and he could not hear him. I was amazed when he told me that. He said it did not work like that on that meter. I forget which it was. Sorry I am jumping subjects. I have a lot to learn.

Back to the less noisy reception I appreciate the replies because now I know what to be on the look out for in the receiver section of a hf transceiver. I may can purchase a mid entry level rig pretty soon.

 

[nanZor]

Brett -- good advice from all.

Basically at night on 40/60/80/160m, unless you have a specific need to, normally you don't run with any of the rigs preamps activated, and in fact either turn down the rf-gain, or use the fixed attenuators believe it or not.

In Yaesu's world, you will also find the "IPO" option. In the marketing department, they call it an intercept-point-optimizer. In the real world, that usually just means no-preamp.

What you are searching for is the best signal-to-noise ratio, not the highest swing of the S-meter. You want to a good antenna for sure, but here is a tip:

One day when you have nothing to do, lightly TAPE OVER the S-meter. Painter's blue-tape will not leave any gunk.

Now adjust the rf gain, attenuator, IPO etc for the most pleasant sounding audio to you. Only flip under the tape and take a peek at the s-meter. You may be extremely surprised!