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Tuners and Preselectors

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chrissim

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I have some understanding of the basics of both, but what I really want to know is do I need either for receiving purposes only? This is one of those hobbies, it seems, where there are so many different opinions that it becomes frustratingly overwhelming.

I have used an MFJ-959C. I never found that it brought in a signal I couldn't hear without it. The tuner amp function only serves to increase noise level along with audio level.

I do worry about resonance. The Pixel loop I use is, according to Pixel, tuned. Nothing more necessary. The Par Electronics SWL antenna is a long wire, and perhaps that might benefit from a tuner/preselector. My understanding is that such devices as a preselector will, if I understand my terminology, match an antenna to the desired frequency. This would have me assume that I need a preselector or tuner, though they both seem to do something different. A preselector seems to be the best option, but I don't know - which is why I am asking.

Honestly, the biggest improvement to my listening has come from a West Mountain Radio CLRdsp filter (that thing really works well).

If it matters, the antennas I normally use are: Pixel Pro 1B, Par Electronics SWL, and a DX Engineering ARAV3-1P. My HOA frowns upon unsightly contraptions, and these have been the best antenna options for me in my neighborhood.

Thanks for your consideration.
 

LtDoc

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A 'tuner' is only an impedance matching device, that's all it does. It doesn't really 'tune' an antenna, you have to do that at the antenna it's self. As far as a 'tuner' is concerned, everything connected to it's 'antenna' terminal is an antenna. That's including feed line, switches, everything from the tuner it's self to the tip(s) of the antenna. If using a tuner makes a signal 'better'/stronger then there's a problem with impedance matching between parts of your antenna system. For an mismatch to be great enough to make a noticeable difference in signal strength it means there's a 'bigger' problem in that antenna system. Fix the 'problem' where that 'problem' is, not where it isn't.
A pre-selector only does amplification, it doesn't do impedance matching. As you have found out, it can't distinguish between a desired signal and one that's not desired. It just amplifies everything and you have to do the 'distinguishing' between desired/undesired signals. That's something a DSP filter does if you can tell it how to distinguish a 'good' signal from a 'bad' signal.
Complicated'er and complicated'er, aint' it?
- 'Doc
 

chrissim

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Thanks for the reply, Doc. I don't know that it's so much complicated as it is overwhelming in terms of the different opinions. I've read incalculable amounts of information on the net regarding the subject and I'm telling ya, I've read as much for as against tuners and preselectors. You'd think anyone really well versed in antenna theory and the like would be able to conclude one way or the other, but I am yet to find any real decisive argument for one over the other.

In my extremely novice and elementary understanding, if one has an 84 ft. length of wire (for instance), that wire needs to be made to match the band one is listening to; essentially shortening or lengthening the wire. For this to happen, either a tuner or preselector is needed. If one of the two isn't used, then one would be forced to install numerous antennas for nearly every band (and some do). I like compromise antennas - I'd rather have a couple that do everything acceptably than an antenna farm in which various antennas are erected to serve a single purpose. Okay, perhaps I wouldn't mind a farm, but my HOA would arrive at my doorstep torches in hand. I've also read that if the correct balun is used, no tuner or preselector is needed. Added to that, I gather much of this is a non-argument if it's all for receive purposes only.

I don't know that it all really matters in the end. I was concerned at first with the Ohm factors of RG6U and RG8X where one of my splitters calls for 50 Ohm input, yet I've used 75 with no problem or discernible difference. I like to think it's all a marketing ploy to drive hobbyist over the edge financially, though I am likely, and unfortunately wrong.
 

hertzian

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Maybe a simplification will help in determining the difference between a preselector, a tuner, and an amplifier.

Preselector - usually an unamplified tuned circuit, that is more suited for bandpass filtering rather than antenna tuning. In other words, the rf amplifier in your radio works best when it is not exposed to the entire spectrum well above and beyond what you are tuned to. Most good radios have a handful of internal bandpass filters that divvy up the spectrum among smaller chunks. Cheap radios may have just a few or even none at all exposing the amplifier to the whole swath of spectrum leading to overload, desensitization, and other numerous ills. A preselector was popular in the day for cheap radios, or for those inundated by immensely strong out of band signals as an additional filter.

Antenna tuner - while made up of much the same materials as a preselector (capacitors, inductors), it's intended function is to act as an impedance transformer, rather than wholesale bandpass filtering. But yes, it will act like a preselector, but is usually much narrower in scope.

Amplifier - as you've found out, an amplifier merely raises the *overall* signal level, including the noise. Ideally it should raise them equally. Some poorer amplifiers will add a lot of their own noise to the equation.

An untuned small loop, while having great directional characteristics, on it's own usually has very weak signal levels, and can benefit from either amplification, tuning, or both, whereas a large outdoor antenna may not need this at all dending on propagation, frequency, and time.

That being said, for the antennas I use, I find a so-called tuner quite valuable. While it merely does impedance transformation, and does not drastically change the signal to noise ratio, the increase in *overall* levels (mother nature notwithstanding) due to a matching of the receiver to antenna system impedance, allows me to listen to stations earlier when the band is opening, and longer when the bands are closing.

If you don't need amplification, don't use it! For example at night, when listening to signals below about 10 mhz, there is usually no need for amplification (my preamps are always off at night), but again, it depends on your situation, so there is no hard and fast rule which leads to a lot of threads pro and con. You are the one in the driver's seat, not us. :)
 
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majoco

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For a 'tuner' (aka antenna matching device) to work properly you should bring your antenna wire down to the 'tuner' - no coax cable. The 'tuner' effectively lengthens or shortens the antenna wire by adding inductance or capacitance and transforms the antenna impedance to the input impedance of your radio - usually 50 or 75ohms.
As soon as you have a matching transformer and coax cable feeder to your radio (PAR SWL antenna for example) a 'tuner' will work as a pre-selector (bandpass filter) as you have already converted the impedance of the antenna down to some lower figure by the action of the transformer.
If you connect your random length wire directly to a bit of coax cable down to your radio, you will be losing some/lots of signal to ground due to the capacitance of the unmatched coax. Unfortunately coax is the best way to avoid induced interference from your house wiring/lights/switch mode power supplies so your PAR is about the best you can do unless you want to move out into the woods and use battery power!
Never mind paying lots of hard earned dollars for a PAR, you can make your own by home-brewing the matching transformer.....
www.dxing.info/equipment/impedance_matching_bryant.doc
 

ka3jjz

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Let's refine that definition of a preselector a bit - there were, at one time, both passive and active preselectors on the market (if memory serves, McKay/Dymek sold a passive one for a time, and I think MFJ sells one today as a 'passive' preselector - whether it really is or not is open to debate).

Passive preselectors had no amplifiers, but acted more or less as a tunable bandpass filter. It was very effective for receivers that were very prone to imaging and other mixing issues due to poor design.

Active preselectors, on the other hand, do have amplifiers, and the better ones are tunable (Palomar had one, I believe called the P-305 or 308...). As stated before, these preselectors can amplify noise as much as signal - and this is where experience comes into play.

Those that were the real good ones had a variable gain control, so you could control the amount of amplification. It takes a while, but you eventually learn to increase the gain only as far as you need to receive the signal (notice I didn't say 'loudly' or 'clearly'). This comes with time using your receiver, and becoming very aware of the noise floor (which can and sometimes does vary - it's influenced very much by the design in the receiver as much as the ambient noise floor, which could be anything from some noise in the household to solar-induced noise). Usually the AGC in a receiver would flatten out these responses, but in some cases you can disable it - and you would ride the RF and AF gain to get the signal to (hopefully) come out of the mud.

In most cases, a 80-100 foot wire mounted away from the home as far as possible is going to be the best way to get started. Tuners/preselectors really aren't needed all that much for today's receivers (unless the antenna design requires it for some reason). But if you're using a compromise antenna, they *sometimes* can be helpful in digging out that last bit of signal

Mike
 

a29zuk

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Your second paragraph in your first post sums it up. Listening to HF is more about signal to noise ratio. Listening to an unamplified signal of 4 s-units with 1 s-unit of noise is the same as an amplified signal of 7 s-units with 4 s-units of noise. You would only have to increase the AF gain of the unamplified signal to hear the same.

The preselector, as ka3jjz states, will keep unwanted signals out of your path to hear the wanted signal.

An amplifier or tuner may pull a 1/2 s-unit signal out over the top of the sythesizer noise of your receiver so that you can hear it.
 

Boombox

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FWIW, I home built an antenna tuner for my old Realistic DX-160 and it did help reduce images when using a long / random wire antenna (the DX-160 is a single conversion radio).
 
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