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Soldering a pin in a BNC whilst radio is in the tray

Just use RG400 How much do you need? I have been sitting on a good length of it since 2013. I can send you some.

If you put the connectors on first, you won’t be able to run it through any tight spaces, and it might be too long (messy) or worse still too short.

The diplexers I have seen in GA are BNC, yes.

Have you checked with a meter whether the existing cable is shorted to ground?

Administrator
Shoreham EGKA, United Kingdom

So my in line BNC connectors were soldered perfectly, it is not the radio. (As I swapped the radio in the tray for my known working spare).

So it can only be the coax which is 40 year old RG58 which has visible oxidation on the braid where the old balun was grounded.

I propose to run a new length of HDF200 . It’s only VHF, “receive only”, perhaps an 8 metre run as the antenna is on the tail so perhaps a decent 5 mm cable like this is OK? https://www.solwise.co.uk/wireless-coax-cable. What do you think @Peter – you will no doubt have strong opinions on cable but Solwise will put the plugs on which saves messing about.

I used to have dual NAV comms so is it likely the VOR/ILS antenna went into a diplexer? I need to get remove some trim panels but would this be a typical installation?

I’m assuming the Diplexer has BNC connections? Any help welcome.

United Kingdom

I swapped the radio for my “spare” and still the same issue. I’ll check the connection next, I obviously messed up and/or a tiny stand of braid got in the wrong place and shorted the connector. Unusual as I am careful.

It was definitely a solder plug/socket but let’s not start the “crimp” vs “solder” debate again (I’m an old school solder guy)

United Kingdom

alioth wrote:

All the RF connectors (BNC, TNC, N, SMA) I have use a soldered centre pin and crimped shield. (You can usually tell if the centre pin is designed to be soldered – it’ll have a little hole in the side of where you poke the coax centre conductor).

I was really talking about the braid etc rather than the centre core – which is obviously trivial to deal with by comparison.

alioth wrote:

You can usually tell if the centre pin is designed to be soldered – it’ll have a little hole in the side of where you poke the coax centre conductor

Actually, such pins are used for both soldering and crimping, and crimping guides explicitly say this hole should be used to check for correct wire insertion depth.

All my Garmin stuff uses the machined pins though, none of the stamped stuff.

This is Garmin G5. The pins are stamped, which is revealed by tiny slits at their tips.

Last Edited by Ultranomad at 30 Jun 14:21
LKBU (near Prague), Czech Republic

Yeah but you’re not touching it to the MOSFET input (unless you’ve got the radio out of the tray, and in parts), you’re touching it to some wire (in this case, the coax feedline) which is some distance away, so there’s nothing that can be “instant” – you’ll necessarily have some rise time involved plus an incredibly high output impedance and the voltage will just never rise more than millivolts when it gets to the FET. And I guarantee there is some band pass filtering before you get to that FET on any radio.

Last Edited by alioth at 30 Jun 13:42
Andreas IOM

Actually I think crimping is a whole lot more critical than most believe. The technology has had decades of R&D sunk into it, to make it fairly reliable. Especially with some pin types; notably the cylindrical ones (popular on the expensive Positronic connectors). About 10 years ago I sat in wigglyamp’s old shop for about 3 hrs, crimping an adaptor / bus extender for the KC225 computer, with the special DMC tool shown here

the radio’s centre RF pin to ground will be 50 ohms

Maybe, maybe not. Look at the link I posted. There is no 50 ohm terminator in a KX165A GS receiver. There is an inductor (“zero” DC resistance) which may be ~50R at the GS frequency (can you terminate a transmission line with an inductor??) but who knows what this other radio has?

There is also the scenario where the tip is charged to the top of the mains cycle, say +320V, at the very instant you touch the soldering iron on the MOSFET input.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

A soldering iron whose bit is not earthed will have some capacitance – probably of the order of 100pF – to the heating element so the tip will have some tens (or more) volts of swing on it.

Are you sure? At 100pF, the impedance presented to 50Hz will be on the order of 30 megohms – the radio’s centre RF pin to ground will be 50 ohms, so the voltage leaking through the mains will be utterly minuscule. Tens of millivolts swing perhaps.

Last Edited by alioth at 30 Jun 13:08
Andreas IOM

stevelup wrote:

More to the point though, why would you solder a BNC connector in the first place? They are intended to be crimped.

All the RF connectors (BNC, TNC, N, SMA) I have use a soldered centre pin and crimped shield. (You can usually tell if the centre pin is designed to be soldered – it’ll have a little hole in the side of where you poke the coax centre conductor).

All my Garmin stuff uses the machined pins though, none of the stamped stuff. I have a special crimp tool for the machined pins.

Last Edited by alioth at 30 Jun 13:05
Andreas IOM

Peter wrote:

Otherwise one needs a collection of crimp tools, and the crimp versions of the connectors are vastly more expensive.

Coaxial connectors seem to cost more or less the same for crimped and soldered versions.
Crimp versions of D-sub and the like may indeed be costly when using machined pins:

On the other hand, according to what I have read and seen, gold-plated stamped pins for crimping:

are sufficiently reliable yet inexpensive. After all, who am I to judge Garmin if they use stamped pins in their avionics?
As to the tooling, expensive military-grade AMP, Daniels and the like are excellent, but essentially you are paying for a fool-proof design; if you know what you are doing, industrial-grade tools for 1/10 the price will do the job just as nicely.

LKBU (near Prague), Czech Republic
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