Why do CQ WM50HTd Ceramic Filters Die like Flies

I have had a run around with the CQ WM50HTd Ceramic filter which is fitted in the Motorola T3. Yaesu and other Ham Radio gear have trouble too with better known manufacturers offering.

See my post Motorola TLKR T3.

To me the Pattern of failure seemed to indicate corrosion. One poster on a forum had 3 out of 4 Radios fail between last use and the next switch on, some have mentioned electromigration others excess current actually causing fusing (like blowing a fuse) at switch on..

I dissected the faulty filter.


Only at one end there is a copper / phosphor bronze pressure plate with windows in it, the silvered plate adjacent has verdigris on it from the copper one.
Hmm, corrosion inside a hermetically sealed box ? Rubbish sealing by a rubbish manufacturer more like, plus maybe contamination in the manufacture.

I was not gentle in my opening of the filter I was expecting a hard plastic box so I crushed it in a small vise. This revealed that they had used a soft thermoplastic. This may well explain the breaking of the hermetic seal. SV8YM see below was more careful with his dis assembly he says the pressure plate “keeps everything pressed together when the filter is in its case” that pressure on a soft thermoplastic box will cause the side to bow thus opening the filter to moist air and removing the pressure required for it to work. There is a common factor in the filters taken apart, verdigris on the copper plate. Additionally I think the seal is breaking at this end.

Soft thermoplastic housings are a real pain. From the humble 4 cell battery holder where the cell sticks in the molding despite the spring pressure behind it and the plastic at the positive end moves away, to my Alinco hand held, the accessory 6 cell battery holder gradually took on a bowed shape due to fat NiMH cells and finally split. Maybe I have the only metal clad cell holder, my way of extending its life.

Idiots in manufacturing is not limited to Electronics, a £600 caravan roof vent has a winder mechanism to raise and lower it. The winder drives cogs which mesh into a Bowden cable type worm, the cable needs to be pressed against the cogs so the manufacturer molds a dome on the inside of the gearbox. The gearbox is soft thermoplastic so in a very short time the side with pressure bows and the cogs slip. With that we have a gap open up on a grand scale 3 to 4mm wide.
What ever happened to the proud designers and engineers, things could still be made cheaply using proper materials.

I found more information on the subject of filter death after my dis assembly, it is interesting to find that SV8YM considers it is electromigration, he has found consistently that the filters show a measurable resistance leak to earth. My one instance measured truly open circuit and all ceramic elements and plates were almost clean except for the odd tiny spot of corrosion on the metal plates. The copper / bronze spring and the adjacent plate are clearly the originating place of corrosion.
In my instance the thick ceramic plates only have a small circular silvered contact area on either side, no chance of corrosion salts shorting across the edge of the plate with those.

There is also a theory about applied voltage causing problems, I have no circuit for the T3 so I don’t know if there are DC blocking capacitors. Actually there is no need for an external voltage, we have a dissimilar metal cell with the copper plate and its adjacent one which can generate its own voltage when the radio is off, the T3’s spend more time off than on so they decay due to electrocorrosion in storage, ready to be dead when needed for use.

Two simple things would certainly help make more reliable filters, a long spring clip made of a non dissimilar metal across the whole stack.
Or a non dissimilar metal version of the present one and a rigid plastic box with the base heat welded for a reliable seal.

I was surprised when looking for a UK supplier by one of the distributors terms and conditions of supply for ceramic filters. Prospective purchasers had to sign a declaration that they were not for use in any application where reliability was critical. Obviously all is not well in the ceramic filter world. The more you look the more you find out that is so.

Read the interesting story from SV8YM here Withering Filters.

One of the Mothers of WTV’s on VHF 2m WSPR

Some of the first comments made about screen grabs reported to be showing WSPR Wing Tip Vortex Reflections was that this is an AGC effect.

I have not before found a signal on 2m strong enough to pump the AGC on my Kenwood TS790 until today when my mast was up and I turned my beam on G3XJV just 46Km away who was running 100 Watts.


Note the common start shift of the artifacts with two adjacent WSPR periods (marked with orange lines) there is a 2minute TX period between these two transmissions, any external effects (WTV’s) from Aircraft would have carried on in the same direction or faded away not restarted with the same shift at the start of the next transmission.

G3XJV was a good 0dB signal on the back of my beam and as I was beaming across the N/S UK corridor there was much Aircraft Scatter no less than 12 separate planes at one time.
I turned my beam toward G3XJV and his signal is between +4dB and +13dB.
I can hear the AGC pumping and captured the effects.


In an impromptu test, was G3XJV watching my Grabber, he dropped his power to 2W the same level as mine and the ‘WTV’s’ were no more.


Motorola TLKR-T3 446MHz Radios

When I had a need for some 2 way 446MHz Radios for camping I considered the local off the shelf rigs but decided I would go for the big brand Motorola TLKR-T3.


The radios have had minimum use but they are handy for the times when we need them, unfortunately one of the radios stopped receiving so I decided to take a look at it. It is always good to Google the problem, I did, there are several queries the only replies are ME TOO, lots of them.
There are no offers of help, no cures, no circuitry available, not even a layout diagram.

Being cheeky I asked the Director of a PMR repair company the question, ‘Motorola have a problem any clues as to what it is please’. What a grand fellow he is, he replied on a Sunday, it seems that the 450KHz filters die like flies, he put his guess at 99.9%.


With that information I looked up the filter type No. CQ WM50HTd on Google, it is 450KHz BTW. Here we go again one poor guy has a set of four of theses rogues, one day when they were needed 3 of them had thrown up the same fault, no receive, and yes it was the filter in each one.

A bit of extra information was revealed by him too, I hadn’t noticed, remove the rubber keypad and the PCB is marked Uniden the true Chinese producer.

The 450KHz filter a screen and 2 Xtals are fitted by hand soldering, in the radio with no receive the soldering was disgusting, component leads were blackened the joints dry looking with vast amounts of black clinker around them.
I opened the radio with no problems, the majority of the hand soldered joints looked OK, however an HC49 Xtal had been thrown at the PCB it stood high at one end its lead resting unsoldered on the gold pad on the component side, the other lead just made it through to the underside where a dome of solder was placed, I gently touched the Xtal and it merrily rotated on its one nearly soldered lead.

So much for Motorola’s brag of extended life vibration testing.

OK so lets look up the filter, Google is our friend they say. Not for this kiddy, no listing no data, no connection diagram, no indication of equivalents (the pinning will most probably be different) its not even clear who makes it, maybe the CQ indicates Chequers Electronics in China, they say they supply into Eastern Europe not the EU.

I wonder if there is a way into the Motorola closed shop for spares.

I find it interesting that some Ham Transceivers have problems with 455KHz Ceramic Filters often the wider FM ones, the Yaesu FT857/FT897 suffer I am told. It is said that the cause of failure is electromigration, I have it on very reliable authority that this is not the cause.
How about cheap copies of decent filters by some obscure set up in China manufacturing in a non ideal environment, somewhat like the soldering process used to fit them.

UPDATE 12:09:14

The actual CQ WM50HTd remained illusive so I intensified my search, there is a Polish EBay seller who has Murata equivalents from his illustrations it looks as if they have changed the size and pinning of the latest ones, CFWLB450KHFA to match the CQ pattern. I have nothing against buying from Poland but it may take time and the postage is five times the price of the filter. I could buy them from a distributor in the UK but I want one not 1,000.
Previous Murata filters are in the CFWM450B to CFWM450I range slightly larger and with different pinning. I found an EBay seller in Wales who has some CFWM450B’s, the B/W of these is too wide. However this will merely give us more audio B/W and maybe a bit more noise, if these were Yaesu Transceivers I would want it right, but with these,do I care? Additionally a strong signal on an adjacent channel could open the squelch or we may hear splatter again do I care? Actually to hear someone on our travels would be a minor miracle.
So for the sake of £3.50 including postage (it arrived next day) I took a gamble. The CFWM450b is physically a bit too wide but it fits in the gap, the input pin is on the wrong side, the pinning is 1 pin on the left 4 on the right, the original is 2 on the left 3 on the right so I had to cut the input pin down and put a wire link across underneath to the hole for the pin. The CFWM450B stands a little higher than the original and once you have fitted the wire link it sits a little bit higher still, there is room if it wasn’t for a small reinforcing web in the plastic back casing, that was easily chopped back to half its depth and the case half fits fine.

On test, sure enough the repaired one is louder than the original and the squelch comes up when the other TX is keyed up in the same room on an adjacent channel, performance is however fine for what we want and probably for longer range too.

Edit January 2018 When I came to use the Motorola’s after a period of storage the other receive side had packed up, I have not bothered to investigate.

VHF 2m WSPR ACS and Wing Tip Vortex Reflections WTV’s

Following my previous post showing my IC706 generating its own spurious signals on RX with no antenna connected.
I have now seen a newer model than mine IC706, with external oscillator locking producing spurious signals on transmit.

Images are full size for best detail. Right Click and select View Image for extra view.

Compare the captures above with claimed examples of WTV’s and other strange signals received in the US below.

I think both TX and RX used in the poor quality capture above were IC706’s with external GPS locking. Note the mixer products produced when there are 2 WSPR signals present (last WSPR Frame at 17:24).

For real evidence of WTV’s I consider we need out with the external locking and out with the IC706’s.