By Jason Reilly.....

 

May I pose a question to you?  What do all radios, without exception, need?  Well done if you answered 'an antenna'.  This also implies that you will need a good connection between that antenna and the receivers front end.  This article deals with keeping that connection good.  In the main, it will apply to handheld scanners and amateur HT's, but could equally be applicable to any radio where an RF connector is being constantly stressed due to constant antenna attachment/removal or changing.

 

If you use a handheld scanner like I do, taking it just about everywhere, you will find yourself swapping antennae many times during a day.  As an example, in the morning, I walk to work, and I find that a super flexible UHF quarter-wave antenna is most convenient.  At work, in the car, I have a mobile antenna with BNC connector for the job.  Again, walking home, the UHF quarter-wave comes into play.  At home, a 1 metre telescopic whip gives me better performance, and at times I connect a HF longwire for some non-serious shortwave listening.

 

Think about the effect this will have over an extended period of time.  Dirt will begin to accumulate on the contacts of the antenna connector of both the scanner and antenna in use.  This will eventually mean that there is a less than perfect connection between antenna and receiver due to the metal contacts being contaminated.  Another possible effect is the connector on your scanner/HT/whatever will become loose, and loose it's earth connection, the centre connection or both.  Obviously not conducive to good RF performance!

 

Think of that little BNC connector as being your radio's window to the outside world.  That window allows RF to enter the receiver, and if the radio happens to be a transceiver, allows RF to escape to the world beyond.  If that window is dirty, you clean it.  If it is broken, you replace it, just the same as with a real window.

 

For a dirty BNC connector, you will need these things to clean it:

 

• small cotton tipped swabs/buds
• small quantity of Isopropyl alcohol or a non-corrosive solvent cleaner
• fine, densely woven cloth
• a couple of toothpicks

 

Isopropyl alcohol can be bought from a pharmacy.  Say that you want this substance to clean electronic equipment so as to not arouse suspicions as to why you want it....  An alternative to this is using some window cleaner fluid, ensuring it is non-corrosive.  Begin by dipping the cotton tipped swab into your cleaning fluid and giving any of the inner surfaces that you can get to of the BNC connector a good clean.  Take a dry swab and dry off the parts you have just cleaned, and to remove any remaining dirt.  Next, take the toothpicks and break the sharp points off them (just the tips, so that they won't puncture the fine cloth).  Moisten a small area of the fine cloth with some cleaning fluid, and place this over the end of a 'blunted' toothpick.  Insert this point with the moist cloth over it into the centre contact part of your dirty BNC connector to clean it.  Using a dry part of the cloth, repeat this procedure to dry and 'dry polish' the contacts.  It's a crude, cheap but effective way to clean your contacts.

 

What if the worst happens and your radio requires replacement of the BNC connector?  The only thing to do is to 'play doctor' and perform electronic 'surgery'.  What is the diagnosis for a connector transplant?  Symptoms include loss of sensitivity of the receiver, loss of power for a transmitter (possibly the casing getting too hot due to the mismatch as well), and the obvious physical looseness of the connector.  It's a fair bet that if your connector has come loose, then a connection to the PC board inside has been fractured or broken.  The loss in sensitivity could be almost indistinguishable on UHF, but quite pronounced at VHF, or vice versa.

 

To take you through a BNC replacement procedure, I'll take you through the method I used to replace my Yupiteru MVT7100 BNC connector.  All radios will be different, but the same general principles will apply.

 

The first step is to write down any frequency/memory information contained in the radio, as you may lose this during your operation. 

 

The next step is to find a suitable replacement BNC connector.  If you are lucky like me, the replacement connector will not be a special sort of BNC (no short 'back end' or ring-nut securing method or any other number of variations) in which case, the connector available from your local electronics supplier will be fine. 

 

It pays to get the best quality connector available.  If you are unlucky, you will have to go to the original manufacturer/supplier of the radio to source a replacement.  You can determine if your BNC connector is a common one or one that you will have to specially order by simply opening up the radio and physically inspecting the back end of it. 

 

Things to look out for are: short back-ends (the bit that hides inside the radio), smaller than usual centre solder conductor, two locating chamfers instead of one, ring-nut securing on the top side of the connector and other similar non-common things.  You may be able to adapt a common BNC to fit your situation, possibly by shortening the centre conductor, filing an extra chamfer onto the thread, or adapting the casing of your radio to suit the common style BNC.  It will all depend on how confident and how neat you are at performing such surgery.  As an example, I was able to replace a TX-475 Electrophone handheld BNC connector which originally used a ring-nut securing system on the 'outside' of the connector to a garden-variety nut and washer on the 'inside' BNC connector without any trouble at all, due to the space being available.

 

When you take apart your radio, be aware that static electricity is the enemy of modern semiconductors.  If you can use an anti-static wrist strap and matting, do.  If not, earth yourself to something that you know will give you a static shock to drain any dangerous static build up away.  Wearing natural fibre clothing and working at a wooden bench will help reduce any further build up while you are working on your 'patient'.  A similar natural fibre cloth laid down on the table to work on will help reduce any scratches to the face of your radio.  Take any batteries out of your radio, if this can be done.  If the radio has an internal battery pack such as the Icom R1, then this should be removed as soon as possible once you have the radio opened up.  OK, then, time to open up the radio using the correct tools, usually a phillips screwdriver.  Be careful of any ribbon cable connecting case-halves together, or of any spring-loaded buttons etc. that may fly out.  Open up the case carefully and slowly, noting the position of any unequal length screws and of any removable internal cabling, if you need to remove it.

 

At this stage, you may be able to see the back end of your BNC connector and may even be able to see the extent of any damage.  Lucky you if there is enough room to replace it here and now!  Most often, however, there will still be other circuit boards and/or shields to remove before sufficient access can be gained to remove the connector.  Sometimes these circuit boards are joined using ribbon cable, and can be removed from the casing of the radio without undoing these ribbon cables.  Other times, the PCBs are interconnected using pins and things that look like half an IC socket.  Pry these out really carefully, as there is the danger of bending/breaking the PCB that they are connected to.  I've even seen flexible circuit boards in use, in which case the whole assembly can be lifted out sometimes.  Again, take note of any removed connections and where they go, and any screws that hold PCBs and shields in place and where they go.

 

If at this stage you see that the centre solder conductor of the BNC has fractured, don't simply resolder it and retighten any locking nut.  Something caused this to happen in the first place, you need to prevent this from happening again.  Replacing your worn BNC connector is probably your best option here, if that is possible.  Otherwise, reusing the original is fine if the connector itself isn't damaged in some way.

 

Once you have enough room to access the back end of the BNC connector, you will need to unsolder it.  A fine to medium-fine tip for your soldering iron is best, since it can fit into tight corners and it makes a neat job.  It is probably best to unsolder the centre pin first, do this by using a solder sucker to remove any large amounts of solder, then finish the job off by using some solder wick.  Heat any joins up quickly and in one action, so that minimum heat is transferred to the PCB.  The earth connection of the connector is next, and it will probably have more than one solder point.  Once this is done, you can remove any securing nut still holding the connector in place.  For ring-nuts, you may be able to use the points of a pair of needle-nose pliers to undo it, but it is best if you can source the correct tool for the job.  Remove the old connector and clean up any solder points on the PCB that you had to unsolder.

 

My Yupiteru was fairly straight forward to do.  First, make note of my frequency memory information, all thousand of them Down with my anti-static earth mats and on with the wrist strap.  Remove the batteries.  Remove the case using a fine phillips screwdriver, and note what screws go where.  This step was a bit tricky due to some plastic clips holding the case together and a protruding earphone connector.  The case was encouraged to come apart using a cloth over the end of a flat-blade screwdriver to gently prise the case halves apart, squeezing the case over the earphone connector.  Next, inspect the BNC connector, which is now visible.  From this I could see that a 'garden variety' BNC connector would do the job.  After having purchased one of these (I purchased mine from Dick Smith, which is of good quality, although I had to sort through a couple to find one packet with all the bits, and in good condition), it was back to the operating table.  The next job was to take some of the other PCBs out to allow me enough room to replace the connector.  The Yupiteru uses those pins and sockets to connect them, and prying these apart took some gentle persuasion and lots of time.  As luck would have it, the very bottom PCB (of three PCBs) was the one carrying the connection to the BNC.  On the second PCB, I found it necessary to remove the volume and squelch and rotary selector knobs and undo the ring-nuts that held these in place.  I cheated and used some fine needle nosed pliers to remove these ring nuts.  I only have ring-spanners for BNC and Siemens type connectors.

 

At last, the final PCB is exposed, and the full extent of the damage is evident.  The locking nut had come a bit loose, and the centre pin solder connection didn't look bad, but I knew it was intermittent.  I could twist the antenna and the signal level would jump up a bit, so I just knew something was wrong.  Next, unsolder the centre pin, not too much solder here, so the solder wick will be fine.  The solder sucker has to come out for the earth connection, though.  This is soldered in two places by a specially shaped solder tag, so I decide to keep it and reuse it for the replacement, instead of adapting the new connectors solder tag.  Why reinvent the wheel?  With the solder connections removed, it's time to scrape off the lock-tite that was supposed to stop the securing nut from undoing.  This can be a hit and miss affair, so don't worry too much if you can't remove it all.  Next, using a suitable spanner, I removed the securing nut.  This job was made much easier by the fact that the top panel of the Yupiteru is removable from the case back half.

 

At this stage, I discover a problem.  The original connector uses two chamfers (flat bits) on the threaded part of the BNC, whereas my replacement has only one.  I decided to file out a tiny bit in the solder tab and in the case of the top panel to make it fit, using some of my very fine hobby modelling files.  Now that the replacement connector can fit into the hole where the old BNC used to be, I chose to add a few bits to prevent the new connector from undoing like the old one did.  A coarser star washer was added to ensure electrical contact between the solder tab and the body of the BNC connector.  A slim spring washer was added before the securing nut was done up, and to complete the job, some lock-tite was added to help fix things in place.  The top panel was then slotted back into position, and the solder tabs were re-soldered onto the PCB.  It pays to cut a little bit off the end of your solder every time you go to use it.  Why?  Every time you use the solder, a small ball forms on the end.  Cutting this ball off will expose the flux in the core of the solder ready for immediate action, rather that having to wait for the ball of solder to melt before it can be released to do it's job.  Now for the all important centre conductor.  I paid special attention to making this solder join neat and sturdy.  The skin effect of RF flowing in a conductor still holds true at solder joins, so making a neat looking solder join is more than just aesthetics.  That's all the hard part over and done with.

 

Reassemble the PCBs and any shields, making use of any notes you made as to the whereabouts of interconnecting wiring or the like and replace any removed knobs etc, and put the radio back together, and the job is just about done.  You may want to take the time to re-program your emory information in a more organised way when you do this job.  I ontinually get new frequencies to add, and they tend to become out of order after a while.  This way, you can kill two birds with one stone, so to speak.

 

Finally, you should test the radio to see the improvement in performance as a reward for your efforts.  I found that signals that were once noisy are now quite a bit less noisy, especially on VHF.  And the antenna connector feels much more solid.  A very quick hint before I go:  if you are using the radio in a situation where the locking feature of the BNC isn't needed, such as being used at home on a table top, or in a secure spot in a vehicle with coax feeding your radio, you don't have to twist the lock part of the BNC connector at all.  It will make no difference to the RF performance and will save some stress on the connector from being twisted loose again.