Insight: Chasing Max Smoke Pt.2

Having previously, in the original topic, established the realities and consequences of chasing for max smoke in ignorance and when pointless, let’s look at where you may be likely to be a bit more rational and try to moderately chase max smoke for practical reasons not ego and ‘big dogs wotsits’ status sake.

So, we’ll assume your operating environment doesn’t allow for high gain antennas (I mean actual, not product hyped claims stuff) and like many who actually play by some adherence to rules, where you can site and how you site an antenna is equally or more limited.

First off, knowing the elephant is in the room, let’s address the lossy antenna fix by adding an Tx or bilateral amp to boost your signal.

If you’re using a quarter-wave or worse, so definitely lossy+, any improvement should be at least trying to turn your negative gain antenna system into a unity gain system. No, whacking an amp isn’t a good or sane fix.

For one, it’s a hideously horrible way of offsetting a few dB of loss and quite frankly most ‘leisure’ market destined ‘boots’ have neither any kind of linearity and in many cases are even less clean that of most common ‘CB’ grade transceiver finals (where this hack is commonly employed). So, just as you wouldn’t fix a rotted rope by doubling up with an equally rotted rope, cascading rotton on rotten into sub-par is a very very bad idea. You may be told you’re S points up, but you’re also S points up out of band and in-band p*ssing off other local users.

So fix the ■■■■■■ antenna problem first and always. If you can halve the loss, that’s way better than gaining offsetting half by forced sh*t amplification and effectively wasting half the active gain as heat and out of band emmisions.

Notably, using a high Tx output (and subsequent high FD/SD) can be a killer of masthead and inline preamps used on domestic TV and cable indoor distribution setups. You see, it’s not about power level necessarily (although still a factor) but more a matter of the subsequent EM field and FD and proximity. Back in the day, when we used to can RF devices in metal with subsequently canned modular screening within, things weren’t so bad, but this PPA/ABS plastic shell and ■■■■■■ all subsequent inner screening (cheap-■■■ cost cutting on both counts) obsession we see is just ensuring that it’s gonna be a sob story for someone.

■■■■, I know this well and even I ferked up once - I forgot I had a masthead high grade distribution amp and inductive coupler on the in-house TV distribution due to lousy reception and hostile regs (compounding necessary restriction due to technically being close to an airfield) ensuring I couldn’t get a beam high enough to just offset surrounding hills. One day, I dropped the ball and did a quick 500W test on one of my HF rigs (I rarely use much over 10W, being more a QRP op and TG modes really doesn’t need big stomping power output). That evening, switched on the TV to watch the news, and it was like a whacking great attenuator was fitted. Yep, I cooked the masthead because the TV was on standby and when the set is powered by the wall socket, I insanely wired up the masthead to be parallel powered in sync. Had the TV been powered off at the wall, worst case would have been passive damage potentially but because the amp was active, well it may as well have been an EMP victim. If I didn’t know a few things, I’d have been chasing my proverbial tail trying to source the real problem and what happened.

Note - that tale of woe isn’t just applicable to the lossy antenna/amp scenario, it’s a reality that any very high localised FD can result in. If the EM don’t directly enter the potential victim via direct path (through it’s casing), at very close proximity, you can still get a pretty high SIG carried over coax and/or the power cabling employed through induced current means.

So first fix your ■■■■■■ antenna problem to near or effective unity gain level before chasing active gain . This can be as simple as an alternative type of antenna (assuming you’re not restricted to one type) where you optimise by stealthy relocation (or ditto for existing if just trying to reduce cascaded loss) and a type better suited for directing the emissions where you need them. Dipole is your basic, when suitably located, quick answer - unity gain for ■■■■■■ all cost and easily within the construction capability of the hammer and cold chisel cack-handed type DIYer.

There are other stealthy designs, which need a bit more planning and thought to make work, but remember - some of the best espionage exchange of intelligence happened over stealthy improvised mutant variants of common antenna designs.

Assuming most will use vertical Marconi type antennas (tuned vs earth rather than an opposed duplicate element ground as with Hertzian types), no matter how it’s rigged up and whatever variation that’s sub-wavelength by reference to a lambda*vF full wave size, you’ll want decent radials (a good spread of, more is better) that are a 1/4 wave or better in length. At VHF/UHF, wiring some old telescopic antennas as radials gives an easy adjustable method especially the kind with two-axis bases. It’s a pretty good tidy method which can be replaced by wires or fixed rods when you’ve optimised it.

The layout of your radials also matters, as the spread of them affects how the radiation pattern migrates as it gets emitted. So for full 360 degree even spread (notably so on lossy verticals), you want as many even length evenly spaced radials as is practical. So a minimum of three in a triangular pattern, four is more preferable. If you can drive a rod into the ground where it’s 3/4 buried this can help alter/complement the radials and is your immediately better answer where radials aren’t practical/feasible.

So once you’ve got your passive antenna and feeder setup fixed (I hope you thought about and fitted some low loss feeder, especially over longer runs) with no unnecessary junctions in the way of joiners/adaptors, then if you’re still struggling, then maybe then and only then an amp is a potentially valid fix.

But before you go hammering your PayPal/Debit/Credit source on that oh so attractive hype-fest set of ‘boots’, you really should assess how clean your rig’s output actually is. The figures quoted by manufacturers, regarding harmonic emissions and purity of emissions should be assumed as technical theoretical as best, don’t assume your rig is perfectly in line with the claim. OK, there are exceptions where you can at least have a hope that your rig’s emissions are within required clean EMC specs, but I’d only even think about that on radios specifically tailored for the destined market and service - so, most HQ commercial gear by the big four names and highly regarded (commercially) less common makes are likely to be close as dammit to being safe ground, everything else distrust until proven otherwise. On a similar note, the obscure ‘export’ CB I keep for reference wasn’t your typical dressed up CB marketed to hams on 10m as an import dodge, it was an actual specific 10m design for the band that had inherent wider band capability available - in other words, built to a much higher spec and where user expectations were much more demanding. Even so, it got comprehensively analysed before it was ever air-tested at my QTH.

So assuming your rig is nominally clean or better, emmision wise, then hold fire on that mega hyped amp purchase.

There’s a pretty solid chance it’ll be substandard on many levels - designers of decent kit don’t need to hype, a simple outline of spec and purity specs sells it adequately.

So I would strongly consider it wise that you look (within the market and service sector) for commercial grade items. Whilst there are bad apples, most will be as least within sniffing and lick distance of their nominal spec - that’s what you want, worst case. If you’ve ended up with what are incredibly rare, you’ll get one from such sources that’ll not only be centred on spec but may actually exceed emission and performance specs.

Unless you’re already using a high current feed, mobile use, or a very high current PSU for mobiles used as base or specifically to drive the amp, you’ll want an upgraded PSU or one anyway if yours has inherent rattles and hums as plaques most consumer market CB targeted stuff.

Whatever the current requirements the setup needs, double it at least for choosing your new PSU. If you’re OK with a good worker that’s either not going to manage demand or is near rated at best for high duty cycle loads (FM mode analogue is such), you could go for a replacement higher spec item, or just buy a suitably (double requirements) additional on to drive the amp soley - if it proves to be well and truely clean and stable under half rated load, you could duplicate it for rig power using a second as a replacement.

I used, and still do for mobile lashups, some now very old Pye commercial items what were aimed for 25/50W VHF LMR rigs and that was just originally to put a clean PSU on my original 4W FM CB.

Mentioning the Pye units I used, they were not SM (switched mode) types, with pretty good protection circuits and added extras I wired into add what later became advisable additions. The point here is, if you’ve a choice between a cheap high current SM type (most cheapies are) and a more expensive non-SM type, definitely go for non-SM with a good protection circuit spec. For all their quick shutdown under short to earth characteristics protection and ditto for over voltage and over current protection, they are hideous emitters of stray EM. That’s why HF operators avoid them like the plague, especially given how sensitive HF receivers are too. If you wonder why you get so many mystery burbles and clicks and suchlike through speakers and hums you can’t lose through earth-loop prevention, try shutting down those cheapo power blocks your gadgets use and your computer and monitor and wireless accessories and cordless/wireless phones etc. A lot of the resulting quiet you’ll see as improvement comes from not having all those stray SM PSU emmisions. The only gear I have with an SM PSU is computers where substituted non-SM isn’t feasible. It’s not perfect, but a ■■■■ sight less localised QRM indoors.

Lastly, rating of amp wise, ask yourself - do you really need 50W upwards, maybe with consideration you don’t even need 25W?

So whatever you do, use it’s capability with due caution and respect to other users and don’t go running power extreme when it’s simply not necessary. Odds are, if you’ve improved the antenna setup as far as is practical, you’ve probably halved the output spec of an amp you’ll need for worst case.

So that’s my advise for when chasing smoke is a matter of practical necessity - but do so looking at the devil in the detail as much as the big picture as the devil in the detail can easily bite you embarrassingly and painfully in the ■■■ as a rabid attack dog in full psychotic mode.