Idiots guide to Pre-amp..

Hello Everyone,Just wanted some advice on a couple of items I’ve never used but would like the full s.p
Firstly PreAmps good or Bad?
I’ve seen the ones you get that are installed on Linear amplifiers and also separate units,but as I have never used either I was wondering are they worth cost.I’m thinking about the QRM that I sometimes get on certain frequencies.(That bloody train track down the road..lol)
Secondly Antenna tuners/matchers,My SWR is fine so know worries there (It could be better on the muppets) but that’s life…
Joking aside are they actually worth the effort if you needed a tiny tweak without having to adjust the tip section again..

Thank you Gentlemen.

CT4029

Hi,

Pre-amps do what they say on the tin, however what they don't do well is discriminate between what you want to hear and the noise around you. They are great where you have no noise and can faintly hear stations but only serve to amplify the noise in situations where you have it. Unless you have a perfect low noise environment i'd personally give them a miss.

Tuners - if your SWR is within acceptable limits then why bother..better to spend time setting up your TX side with Good coax and tuning your antenna to be resonate where you want it. 

It may also improve your reception at the same time.

Time invested in my experience is better than throwing money at work rounds or unnecessary tech.

This is just my opinion there's plenty on the subject of pre amps, coax and SWR within the site and I'm certain that members will be along with suggestions and real world experiences that may be of use to you.


All the best..

Preamp will just bring in the noise stronger well that is my opinion.

Thanks Gmonkey,I’ve certainly invested time and money trying to keep that QRM and unwanted hisses,pops and bangs at bay the best I could.
With decent RG213U coax and Common mode choke,Every electricial cable has a clip on ferrite ring.I think it’s just the world with live in with Wifi and other modern toys.The reason why I asked about preamps was to see if I could hear those far away stations that can hear me fine but are radio 3 and signal 3-4 any better.Like the 27 division Iceland I was struggling a bit to hear as he faded in and out.It certainly wasn’t Iceland warehouse on the high street.
I think I’ll just have to suffer the QRM on Am/Fm a little bit longer,SSB is fine so maybe the preamp would be better on that mode.
As for the tuner/matcher thanks for the advice I’ll give that a miss then.

Thanks again.
CT4029

Thanks Alan pilot,Maybe I’ll see if I can borrow one to give it a go.
But as you say it would most probably bring In everything as well as distance stations.Let’s see

Thanks
CT4029

I find the pre-amp quite helpful, as said it will make everything "louder", it picked my background noise up from 1 s point to about 5 s points but in doing so I can actually make out what some of the very faint stations are saying.
I use my pre-amp literally all the time, because where I live, every station is faint unless the conditions are very good.

Hello Hotel Zulu 253,
I was thinking just that about bringing up faint and distant stations and I could always twiddle the RF gain as well.It’s mostly QRM as I’m in the city of London and you can’t fart without someone hearing it as it’s built up so much.Completely different from their and our weather is awful..lol
I’m thinking of getting a One as there not too expensive and what have I got to lose,you never know it may help loads.
Thanks for your advice..

CT4029

If without a pre-amp on and on an empty channel the S meter is reading anything other than zero then you don't want to be using a pre-amp. If you do all you do is amplify the noise too, reducing the dynamic range of the radio and making wanted signals harder to hear.

I have a pre-amp on my Icom 7300 and it does get used on 10m and 12m but that's only because even with it turned on the noise level on an empty frequency isn't even S1.

I could use one on CB in my car because out of town I get S0 and could use a pre-amp to bring in weaker stations from 20-30 miles away better but there's no point because the stations I hear are far enough away that I'm still going to be wiped out by their local noise floor levels so even though I can hear them they'll not hear me..

Thanks Northern Crusader,There’s certainly plus and minus points for the PreAmp,I was looking at those Italian Linear Amps and they come with or without a PreAmp.Now I can see why the one with the PreAmp is a bit frowned upon.

Thanks for the advice.
CT4029

I think others' advice so far explains why I never had any luck with preamps in the distant past. I had one in a b300p and a little standalone one again by Zetagi, but don't remember them ever helping my receive. I am not going to try using one again in these modern times as my quietest noise levels are S3-4 at home, and a chunk of the time I have to contend with this...



...can you imagine what the noise would be like with a preamp. +20 probably 

If you want to wheedle out the weakest signals there might be some other bits of hardware you could try. I say "might" as I haven't tried either yet, but am seriously considering. One is a decent DSP noise reducing speaker. The other is the QRM Eliminator. A combination of the two might be good. The latter though looks it could be a little difficult to set up for ease of use on and transceivers that are not high end Ham units. Plenty of vids on utube if you want to look them up to see how they have worked for others, and think there was a thread somewhere on this forum about the QRM Eliminator.

Antenna tuners/matchers definitely have their uses, and not just for tuning ladders and fences to radiate on frequency  But I would never use one personally just to tweak the SWR of a good antenna that is showing as close enough.

Cheers again SangueG,The QRM I get is about S2-3 and mostly on Am,Fm which is bearable as I’m mostly on SSB.
That’s a great little video and your advice has definitely got the old grey matter working.
Thanks
CT4029

Flipping 'eck Neal! That is some interference. 

I've noticed similar my way but only on the freeband up to the high end of UK CB, once you get to 10m, (28MHz), it totally disappears?!?!? (Similar story once you get down to EU/mid block). On my old FT757 the NB does its job at mostly removing it especially with a drop of the RF gain but sometimes it's bad, other times not there. I know others are plagued too and I've not yet heard a reasonable explanation for it.


Anyway, back to Tom's question...

I played with preamps in my 'way back when' CB days with no luck whatsoever and wouldn't even consider one now.
(OK, maybe a low noise mast head type for higher frequencies but only at a push.)

Victor wrote:

Flipping 'eck Neal! That is some interference. 

I've noticed similar my way but only on the freeband up to the high end of UK CB, once you get to 10m, (28MHz), it totally disappears?!?!?

Same here. That's because on 11m, like the other public use frequencies there's no offence of transmitting interference in a band where you don't require a licence but there is in the amateur bands so manufacturers of devices like switch mode power supplies and those powerline devices that allow you to use your home mains wiring as network will make sure they notch out interference on the ham bands, aviation, military and maritime etc.

I remember when I had PLT interference on the amateur bands from a street over that OFCOM treat it as broadcasting without a licence and the operator of that device is told to cease using it immediately or face prosecution. It was a joyous day when they turned it off.

Well, irrespective of my hatred of preamps (there are sound usages where they are a necessary evil, but they ain't domestic consumer grade BS wideband QRM boosters), I'll simply point out that you'll get more clean gain in the readability clarity end of creating a signal magnet by the use of an antenna that actually is at least unity gain, has some semi or actual directional radiation pattern and associated acceptance angle (so it highly rejects the off angle, so the on angle sources stand out above the band noise floor).

The only time I ever used a preamp in anger was because it's inherent within any sat comms and DBS LNB, but even then I optimised the dish to get the best size/gain and acceptance angle for my purposes, did critical alignment and built an active auto aligner to tweak alignment if SQ deviates beyond a certain tolerance. Otherwise, the only only other good thing on such high end preamps as in a good LNB, is it's a good source of low noise components.

And regardless of where you talk about preamps, if their internal noise level isn't crazy low, you just doubly compound the issue with yet another.

Unfortunately, all my good solid reference examples are SHF designs, using components designed for SHF use, so the designs would be pretty useless to try using below the dark magic zone.

Victor and Conor, unfortunately for me on 28HMz and above it is no better, although on that radio it is loudest and strongest on 25 and 26MHz. The old girl underneath picks up the noise when it's at its worst on much of HF but no where near as bad as on the 6900. Although a lot newer, I think the 6900 is just made very cheaply. It certainly does have a very sensitive receive which probably compounds the problem, just for example I pulled the coax plug out the back and stuck a mini allen key (about 3" long) into the centre of the socket and it still picked up the noise at S1.. and also brought in 161 a div station!

Anyways, I shouldn't hijack the thread. I am working on my problems. Maybe when I obtain my ticket that might help me, but I certainly wouldn't want to involve ofcom at the moment  Just wanted to express my opinion, which seems to match others, that eliminating unwanted noise is more beneficial in assisting bringing in weak/quiet stations than using a preamp to amplify all signals including unwanted noise.

I'm with you there all the way Neal, if you've got noise to start with then a preamplifier is only going to make it worse.


As Conor, (Northern Crusader), pointed out it's a mess all over the RF spectrum but luckily not so bad on the Amateur and protected bands. If you took a look at the spectrum of your typical mains supply it looks like a 'comb' filter arrangement with notches on those protected bands, but 'sod-you-all' everywhere else! .....unfortunately that includes the UK CB frequencies and 'freeband'.   

(Please don't hook a SDR or spectrum analyser up to your mains - I was inductively coupled when I checked it.)


Always worth looking at out own RF mess too. Despite my best efforts to keep mine down I was caught out with my recent interests in VHF....seems my Baofeng charger was the culprit pretty much wiping out all my HF reception! The regulation/charging circuit was fine in the charging base but the mains adapter was spewing cr*p all over the place!
That soon went in the bin and replaced with an 'old fashioned' transformer adapter ridding my noise problems.

No preamplifier in the world would have got around that nonsense!



Nice one with the PLT nonsense Conor, bet that was a HUGE sigh of relief!

As Victor himself discovered, but it's always been a notable issue, switching/switched-mode PSU's are in terms of potential QRM monsters, pretty much to generating QRM to what typically preamps (and pretty much all commercial consumer preamps are junk) to being a Slade PA stack grade SIG+garbage magnifier where the localised presence of both are pretty effectively complementary brothers in arms for making one hell of a mess.

All SM PSU's have the residual QRM monster consequence (only 'residual' here refers to the added local EM it generates as a consequence, not a measure of intensity). It's in the Deep DNA of the breed, and yes it's probably fair to say it could be a reduced problem with some core redesign, but given it's effectively a high magnitude square wave generator, whilst that's inherent to its desired use performance, and they are dirt cheap to build and ultimately it's that CheapoElChips manufacturing cost that has endured the type have become the go-to design for compact high amperage design that overall is barely bigger than it's transformer at the core.

Now there are some items, usually high amperage bargain 'radio market' examples such as Moonraker sell, ML&S too, but these are nothing more than an A.N.Other regular QRM monster in a cage (OK, it's a positive point that you actually give them some facsimile of a Faraday Cage style enclosure) that's got a variable tuning control for a 'filter' which isn't - it's just the equiv of pulling the Square Wave pre-filter output around as an offset much like a injecting a low level SIG into a varacter diode will vary an oscillator output crudely (and that VD and voltage trigger is the core of every variant of what we call an 'FM' modulator in most FM transceivers - where it's true FM when you pull the main oscillator output pre any PLL or SIG mixer, where it's applied to the carrier frequency pre to finals, it's 'Delta' or 'Phase' not FM where each is essentially the same but has a slightly different focus). So essentially that 'feature' just allows you to tweak the output frequency of the SM output to possibly offset enough to reduce maybe one notable harmonic and a few overtones at best.

So short of an old school 'linear' PSU, of which is a brain-death complexity fix for fixing a QRM issue on a low current demand device, the only real way you can tame the residual induced QRM on a radio using SM PSU as a source is to distance isolate the PSU from what's powering it - but you still get some garbage over the power feed.

But given you could safely bet 90% of your household leisure/convenience electronics and electricals are low voltage DC fed, they'll be SM PSU powered.

The nearest I ever got, these days, under screened test room isolated testing, to a high level of reduced localised QRM not caused by the equipment in focus, was battery powered radio with a battery powered SBC which line powered the TNC or other 'modem' used for TG work. And that was only highly effectively not due to what the arrangement was but a consequence of TG communication being highly band noise and QRM resistant.

So aside from TG use of radio, you're going to either accept shutting down unnecessary electronics and respect PSUs when actively listening/On-Air or replace every damn SM PSU used in the house with non-SM types and minimise unnecessary use of digital gear. Or no the same precaution wise but limited time op on battery power. It won't solve the side that's not self-inflicted but given the SIG density/field density of your local QRM sources indoors will be the biggest 'receiver swamp' sources, whichever approach will make a sizable impact and improvement.

Of course, you could go nuts and integrate a house sized Faraday cage within the building structure, like they do in professional comms stations, but that only reduces what local garbage leaks to adjacent vicinities and reduces induced local adjacent induced noise. It certainly does fix the real problem we've all contributed to by wanting dirt cheap electronics and cheap high current light weight compact PSU's.

So, just remember when you moan about SM sourced QRM, you brought it on yourselves.

Maybe it's a topic in it's own right - but it's more interesting than merely cheap to build and ship that makes SM PSUs the go-to quick fix PSU solution, for better or worse (which is pretty obvious).

Where a good 'linear' (aka transformer non-switched type, old school bulky and heavy where you could almost verify it's actual rating by dropping in one someone's foot and discover how many toes it broke..) PSU has an inductively coupled raw ratio transformed and reduced energy (current and voltage relative to transformer ratio), to get real supply protection and regulation protection a d short circuit cut off etc, over current protection, ..., you actually have to add a lot of sub circuits to achieve most of that, and have them crosslinked in various senses to work in a complementary fashion. In other words you go from simple ratio converted regulated x/y power transformation with a few junk voltage regulation to a fairly complex beast.

Now, keeping it fairly simple since there are few uniquely different techniques to generating a sub-output via PWM switching all using a core basic principle, a switch mode PSU has a fair number of what we'd add to a regular design as inherently necessary in SM designs. So universally, you get free (as in by default) short circuit and short to ground cut off what literally stops the PSU dead until you remove load and/or fault.

As it has to self regulate switching of PWM, it's relatively technically easy to provide current limiting and voltage output trimming by merely putting a more complex controllable PWM control in. It's, to SM power gen, what PLL is to SIG gen and actual uses a PLL.

Now because of considerable differences in how much circuit is required to achieve the same regulated end result, a SM often has a much smaller and hence lighter transformer and this reduces it's cost on many levels.

But because a huge amount of added value protection already is inherent to SM and if you start with a breakout of multi-voltage it, it's crazy easy to get 6-10A 12v, anywhere up to 4 times the max current on 5V in parallel and still have a good solid 3.3v of a current rating most radio powering tasks will never need (but don't waste it). Hence why PC PSU's have become popular conversion sources that have a few uniquely catch-out design quirks, but it says a lot about why SM is the often chosen method these days.

But the price you pay for relying on SM types, an EM noisy home that does a pretty good impression of what you'd hear if you listened to a radio near the gear that supplies the traction current to railways - a heck of a racket.

So that's essentially why we're plagued by SM generated noise, and we self inflict ourselves in our goal of cheap PSUs. Part isn't our fault, but if we refused to accept them as the norm, we'd have to stump up extra bucks for our supplied-with-charger gear, but it's worth thinking how much value you put on clean reception and general lack on unnecessary levels of ambient SM induced EM noise in general.

I've seen a lot of them, the bad and the ugly and damned grotesque in EM terms, and really almost hate them as much as the trend of unnecessary use of RF preamps.

I thought this post was about preamps.
Plenty posts about qrm.

Preamps, QRM and PSU sourced self inflicted hell are all intertwined - as are the reasons why poor application and design of preamps (of which few truely of true low noise characteristics exist below SHF usage and they only are effectively minimal victims of near field and strong far fields EAM due to very good design, common application on hyper directional antennas and yet have to bring up SIG's far lower in magnitude that your average weak DX SIG on HF under most conditions) just invites grief of a disproportionate level that can defy belief enough to actually seemingly make conditions look unusable and create utter Rx front-end hell that if you were blessed with the user ability to moderate the gain level would at least help by cracking back the beast which really shouldn't be needed by any half decent receiver.

Add a preamp onto a radio with a notoriously sensitivity Rx and by design optimised to restricted antenna usage in favour of physically and electrically long antenna main use - part of which is achieved by a integrated high gain preamp anyway, and you'll really be in noise and QRM hell twofold.

So you can't really avoid evaluation and discussion of QRM and seriously worsened SNR due to increased wideband amplified internal, local noise and worsening of the effect of band noise and QRM and inevitable birdies that stem from the breed and misuse causing often very severe Rx front end overload.

And given SM PSU's are, since far more common than the usually cited power line converters, the single biggest cause of unwanted and unnecessary EM garbage and crazily external examples of preamps often use SM PSUs as cheap persistent power source, it's bad news all around.

And since, thanks to laziness/disinterest/penny-pinching misery thinking, there's a huge unhealthy denial of why we've so much EM garbage with destroys many half-way reasonable cases where a preamp set up sympathetically could improve normally poor reception whilst worsening overall SNR - we are truly guilty of the hell we created. Where these worlds inevitably collide unavoidably, it reveals how few end users of preamps and PSU's in general realise why SM type QRM/EM garbage generators are both common to both end users and manufacturers as the go-to choice of PSU's. Likewise, few actually seem to know how the 'radio market' PSUs have basically a bodge exploiting how regulation is controlled on SM PSUs to blunt-chisel offer some added value to radio users over non-radio market SM PSUs.

So answering any preamp related question or query brings this stuff into focus as it's all going to affect a preamp end user's experience and any vaguely tangible reasoning for the putting up with the added mess that results vs a cheaper, more effective and generally saner adoption of infinately more beneficial passive gain and directivity/better off-angle rejection coming from a more optimal choice of even limited setup antennas instead. At least better passive gain and a token use of cavity filters and a wider attenuator in the comprised situation of Rx overload is way preferable to blunt-chisel preamps in any context.

But it shouldn't need explaining or detailing and yet it's clearly evident those interlocking aspects need addressing in detail to get perspectives of why preamps are both highly avoidable solutions and yet in limited contexts the necessary evils since, say for DBS pickup and weak signal mode reception, we're not all blessed with being able to use an antenna farm that puts Goonhilly and Goldstone setups to shame.

It took a lot of work this end to make a compromise where I could avoid needing preamps for TV and radio use (bar LNB preamps on DBS and SHF stuff) to both integrate much better phased and switchable hybrid arrays of limited antennas to avoid preamp hell, and QRM/EM garbage is still hell, but at least I'm not deliberately and ignorantly making it worse through lazy-assed blunt chisel fixes to weak SIG operations.