Phil Green

Not really, the principle of dual conversion is simply to separate the required signal from its unwanted image. Using fictitious values, say you have a single conversion rx with an IF of 1Mhz, so your local mixer oscillator runs at 34mhz. The incoming 35 mixed with 34 results in 1mhz which passes through the IF filters, which is a Good Thing. However, an unwanted image signal on 33mhz mixed with the 34mhz local mixer oscillator also results in 1mhz which also passes through the IF filters, which is a Bad Thing. Crucially, since 33 and 35 are so close together, its harder for a fixed front end filter to pass one and reject the other - ie poor image rejection. However... If you up the first IF to 10Mhz and drop the mixer oscillator to 25mhz, then the unwanted image becomes 25-10=15Mhz (bad) whilst 25+10=35 gives the 35 we want (good). Now, the front end can easily distinguish 15mhz from 35mhz as they're far apart, so we have good image rejection. So why bother with the second conversion, why not leave it at that? the reason is to improve selectivity, at 10mhz its hard to filter channels that are only 10khz apart, but if theres a second conversion to a much lower IF then filtering 10khz becomes much easier - 10khz out of 1000khz rather than 10khz out of 10000khz. In a nutshell, the first IF is for image rejection and the second for channel selectivity, to isolate the individual channel coming from your transmitter. The made-up 1Mhz/10Mhz values above just make it easier to explain, the actual values are 10.7mhz for the first IF and 0.455Mhz for the second - this is almost universal in R/C and domestic radios 🙂

In a relatively high-current device like a drill or screwdriver its more about the ESR than capacity, many high-capacity NiMh cells have a high ESR and can't supply the heavy currents 🙂 If it can be made to physically fit, a single 3.7v nominal lithium cell would probably out-perform four NMh AA's simply because it wont collapse under a heavy load 😉

Well, it was new in 1986! 😄 JR ABC-W.pdf

Or, I always liked the Corona synthesized receivers, probably as cheap as a new crystal - I used several RP4S1 and RP6S1's - still do occasionally 🙂

The 'internal crystal' runs the second conversion oscillator, 10.7 minus the second IF which is usually 455khz, so 10.245mhz which is ubiquitous in all but the real oddballs. But this has no bearing on why crystals may or may not be interchangeable between brands, the actual reasons are differences in frequency (1st IF above or below), overtone, load capacitance, and series or parallel resonance. Bear in mind that Hitec, Futaba, Multiplex, JR etc do not manufacture crystals, they order them in to a spec, which anyone can do (and we do!) although these days its become rather expensive and a while lot of our favourite companies like Quartslab, Cathodeon etc have unfortunately disappeared, virtually any crystal can be made to order, given a spec 🙂

Ah yes thanks Brian, my Hitec vs Futaba recollection wasnt quite right but I was sure there was a fundamental difference, its actually that Hitecs have a highside IF (35 + 10.7) and Futaba lowside (35 - 10.7) Its great getting old, isnt it 🙂 but then again its been a while since we needed to remember all this! 🙂

Unless I'm clicking wrong, when you look at Hitec/Futaba/Graupner dual-conversion receiver crystals, it gives you only the transmit crystal spec (?) Tried a few times, maybe its me 🙂 The 17mhz transmit crystal thing may look odd but its to help get sufficient FM deviation, crystals wont pull far but if you double it you double the deviation, in fact my (possibly wrong) recollection is that Hitecs tripled from a 12mhz fundamental.

You cant tell a crystal's spec by appearance, JR vs Futaba. I dont recall either particular spec (its been a while...) but they could have the 1st IF above or below, could be doubled or tripled, could have different loading capacitance, could be series or parallel resonance... of course if you are certain the JR & Futaba specs are exactly the same then no problem 🙂

A smartphone near the transmitter?? 😁😆😁

Manny is compiling a list of sites to register for RID-exemption, we've submitted ours, drop him an email about Cocklebarrow though he's probably already included that one 🙂 As for public displays - actually thats one area where I agree with RID 🙂

From the outset they stated that the 250gm boundary would be subject to revision, though dropping 250 to 100 is quite a move, clearly mass isnt a good measure of UAS capability and was a poor choice for class distinction 🙂

I've only tried Plasticote, no primer, just sprayed it onto the foam (yellow Cub, above)

That particular (mpx) event was confirmed Brian so no argument from me. I wonder what memory component mpx used?

Whilst interfering with an R/C receiver is very unlikely, it is true that in close proximity, phones can induce signals into wiring. So I tried a very unscientific experiment, it proves nothing, but...

Short story, wifey said some pals had extra tickets and we were off to see Quo at short notice. Now I've never been a Quo fan, they're ok, just not my bag, I enjoy any live music but wasnt bubbling. I asked if there was a support band - yes, she said - Roger somebody. Roger Whittaker the whistler? Roger Daltry from the who? again, neither my cup of tea. Any way we turned up, and I saw the posters - "Roger Somebody" was actually Paul Rodgers, one of my all time favourites from the Free days and I reckon one of the best voices in rock. I'd place him alongside the very best - Steve Marriot - Humble Pie's 'Rockin the Filmore' being my fave live album of all time. Paul did almost a complete Free/Bad Company set, guitarist was Geoff Whitehorn who I was aware of through Total Guitar magazine. Superb. So a fantastic evening was had by all, unexpectedly so in my case! 😁

My Tomboy Senior is the same size & probably same weight (28oz?), it has a Blue Wonder, 8x3.8 and 3S 1000mAh, just under 100 watts which is ample. Edit 28oz including 4oz of lead... 🥴 https://www.youtube.com/watch?v=WFfS7AWpvoU

We had 7 up at Baildon yesterday, really enjoyable days sloping

Re 'which receiver' my pal Rob has a Radiomaster TX16, he's used a variety of receivers but much prefers Flysky (Flysky not Frsky), mostly FS-iA6B iirc They need no 'tuning' unlike Frsky's CC2500, theres a wide range in size, shape, #channels, they're inexpensive, have great range & have been utterly reliable. He flies everything from indoor to 1/3 scale petrols. (not my Humbrol opinion but Robs)

A bit of spring tensioning and the same holder will take 2032, 2025 or 2016 🙂

at 459Mhz Geoff you'll appreciate +/- 10.7 is quite close for the front end to filter to separate, and .455 and 10.7 are almost 'imposed' due to availability of commercial filter components. Hence the third IF to shift the image further away from the carrier, 27Mhz away in Reftecs case. I strongly suspect that Reftec receivers were based on a conventional 27Mhz dual-conversion receiver design preceded by a simple 432mhz mixer stage - unforch I dont have any Reftec rx crystals to confirm. In my Humbrol opinion, of course! 🙂 .

Flair Heron 🙂

I do get that, but I just think its a shame to ditch a radio that you're confident with, just for the sake of a broken toggle 🙂 😁 My newest radio, Staveley Deluxe 4:

I have a couple of Reftecs and they do feel cheap and fragile in comparison with the Cotswold which was really well made, a proper engineering job in every detail. I gave my only Cotswold to Paul Howey (the designer) as he was feeling nostalgic and didnt have one! I've posted this before but if you haven't seen it, Pauls site is utterly fascinating, transmitters as low as two-grammes tracking bird migration and Xtags tracking hammerhead shark behaviours... https://www.microwavetelemetry.com/

Its a shame that Quanum disappeared, they did a standalone telemetry thing for electric models, postage stamp sized unit that plugged into the balance lead, and a matchbox sized display you could put in your pocket or attach to the transmitter... it was inexpensive and worked very well. One advantage of being standalone is that you could use it whilst charging to monitor cell voltages remotely, so you could charge outside whilst monitoring from inside your shed.

Why change? You have a reliable system that continues to give good service. Clean the case & fix the broken switch, its a simple job 🙂 .