Goodbye £80 !

[cb4ever104]

So I connect up my little RF Signal Generator as normal to the 360FM that I'm testing . I have the coax cable that connects between the generator and radio marked with a big piece of red tape so that I know not to TX into it . I also make sure that I have no mic on the desk either . So what do I do ? I connect my ext speaker into the CW jack at the back by mistake and shove 12W into it causing it blow it up Just goes to show . No matter how careful you think you're being , there's always a way to **** things up

Anyway . If anyone's looking to give me a late Xmas present , then you know what I'm looking for

[lbcomms]

Been there, done that, only it was a Rohde & Schwarz SML02 that let out the magic smoke while aligning a 50W VHF mobile. It received a selcall tone sequence from another radio being installed in the vehicle install bay (about 20 metres from the RF workshop) and auto-replied with 50 watts of RF goodness

The generator has zero output after that mistake. It was sent back to Rohde & Schwarz for repair and returned working a few weeks later after paying the $1K repair bill.

After that boo-boo, I always use one of these in line with the coax to the radio:

https://www.ebay.co.uk/itm/284503147435 ... R-7PqomrYQ

That's a 10W version, which will handle 12W for a few minutes. The 30dB variant will cut your 12W down to 12 milliwatts which shouldn't hurt any siggen...

[cb4ever104]

Been there, done that

Hi Sue .

I have a -50dB sampler on my TX line to feed the counter . I had the RF sig gen set up for -90dB output directly to the radio . Up to this point I've relied on my common sense not to feed any RF directly into it . But obviously my luck ran out . To be honest I don't feel so bad now after seeing your repair bill . I can buy another one of these for about €80

https://www.ebay.es/itm/293249074852

I know they're not great , but it worked OK for my purposes . I'd like to maybe buy some better quality test gear , but to be honest the RX testing I do is really basic stuff . It's usually just an alignment . For that I can even use another radio nearby into a dummy load .

I opened mine up , but there's nothing obvious to see . It's all SMD , but I tried tracing some bits back from the BNC to see if I could find a blown resistor or cap , but I couldn't find anything open cct . So , I'll just scrap it .

Anyway . It's just annoying . It's like taking money out of your wallet and ripping it up in your face .

Lesson learnt for me .... I hope

Happy holidays !

[bitbang]

Done the same with mine, keyed up the rig by mistake and then did it again to make sure... duh. After this the signal was very low no matter the setting and had to replace the PE4302 IC (had to order 2 lots to get a working IC, lots of faulty ones being passed off as working).

[cb4ever104]

Done the same with mine, keyed up the rig by mistake and then did it again to make sure.

Thanks for that . Yeah . Mine was keyed up for about 30 seconds before I realised what was going on , so I´ve no excuses

Yeah . That's where I was looking . I might buy a couple of those ICs and give it a shot . It's bust anyway . It'll give me a chance to use my SMD desoldering station , which I haven't used yet Where did you end up buying the ICs ?

Don't think I'll be buying these . The postage seems just a bit much

IC.JPG

Sammy

[cb4ever104]

Also. Do these ICs like clip into place ? It looks as if just the base might be soldered onto the PCB.

Screenshot_2022-12-28-16-54-01-289-edit_com.android.chrome.jpg

[lbcomms]

I know they're not great , but it worked OK for my purposes.

That's more than good enough if you don't need to go above 470MHz. I'd buy some myself but half the radios we service are 480-512 MHz, so unless there's a hack or firmware update to take it up to 512 they are not much use to us. A lot cheaper than the R&S (just over $6K locally) generators.

I'd still play safe and use a 30dB 50 ohm attenuator though, and just set the generator 30 dBm higher to compensate. Better than a piece of broken test equipment (especially if it's your only one) if a PTT gets bumped / connector fitted wrongly / stray strand of copper triggers the radio into Tx.

Enough gloom and doom for now though - Happy holidays

[lbcomms]

Do these ICs like clip into place ? It looks as if just the base might be soldered onto the PCB.

That's a QFN (Quad Flat pack No leads) package, and is soldered with hot air. Versions with the large square in the centre like that one are best done with a PCB underheater in addition to the hot air from the top, but they can be done with just one heat source if you are careful and have patience. Also, use Sn62 solder (low melting point, Tin/Lead/Silver) if you can get it, not the Sn97 / SAC305 lead-free stuff.

How it's done:

[cb4ever104]

I'd still play safe and use a 30dB 50 ohm attenuator though

Yeah . I'll look into that Sue . Thanks . The only thing I'm not sure about is exactly how much RF I could pump into this before it went bang . And given the cost , it's not really a test I want to carry out

That's a QFN (Quad Flat pack No leads) package, and is soldered with hot air. Versions with the large square in the centre like that one are best done with a PCB underheater in addition to the hot air from the top, but they can be done with just one heat source if you are careful and have patience. Also, use Sn62 solder (low melting point, Tin/Lead/Silver) if you can get it, not the Sn97 / SAC305 lead-free stuff.

And thanks for that info too . I did manage to desolder some SMD stuff a while back , but to be honest I think I only have 1 , or 2 radios that use SMD . I've ordered 5 of these ICs anyway , so I'll give it a go . That's what this hobby's all about for me . Learning new stuff . Not sure how easy it's going to be to source some of that SN62 solder locally . I did a quick Google search , but it didn't come back with much . I'll dig deeper later , when I have more time .

Thanks again for the help Sue !

[cb4ever104]

Done the same with mine

Did you change both of those ICs ? It looks like it in the photo .

[bitbang]

I changed the one circled in red. To test what one is dead stick the generator on a frequency your rig goes to, set the output to max level, connect up a oscilloscope probe to the antenna socket of a CB using BNC to PL adaptor, set probe to 10x (could just a piece of wire) and probe with the other end the input and output of the 2 attenuators in the picture below.

if you feel adventurous, can adjust the attenuation whilst probing to see if the level changes in and out each chip. in my case the second IC had no output despite having a large signal going in and the attenuation did not change at all. the first one worked fine.
I bought the spare IC's from aliexpress. Couple of years ago they were around £5 for 5 with free shipping.

Good luck!

[lbcomms]

I'm not sure about is exactly how much RF I could pump into this

Datasheet for the IC says 30dBm is the "absolute maximum" that going above will damage it. "30dBm" is another way of saying "1 watt", so 12mW if you use the suggested 30dB attenuator is not going to stress it even slightly.

Not sure how easy it's going to be to source some of that SN62 solder

Specialized solder like that is not going to be found at hobbyist type stores like Maplin / Radio Shack. We get it from Element 14.

- Element 14 Order Code: 419564
- Multicore part number: 362 SN62 5C 0.46MM R 250G

It's not particularly cheap (from memory about AUD$50 for a reel) but a reel lasts for years with normal use, and it saves you from cooking expensive SMD chips.

With that chip though, I'd still suggest a mild (to say 80 degrees C) underheating of the PCB to get the ground plane pad to reflow. No need to buy a proper board underheater unless you do this stuff all the time - and assistant with a hairdryer under a raised board on bricks works well

[cb4ever104]

I changed the one circled in red
Good luck!

Brilliant . Thanks for that . Should save me some time . Yeah , I've bought 5 too . Should arrive next month some time . I'll keep you posted .

With that chip though, I'd still suggest a mild (to say 80 degrees C) underheating of the PCB to get the ground plane pad to reflow. No need to buy a proper board underheater unless you do this stuff all the time - and assistant with a hairdryer under a raised board on bricks works well

OK Sue . Thanks . Not sure how I'm going to go about this yet . I'll wait till the parts arrive and sort it out then .

Thx

[Techquest]

PE4302 is discontinued there either going to be old stock if you can find a trusted source or there going to be pulls.
PE4312 is a drop in replacement and still in production.

[cb4ever104]

PE4302 is discontinued there either going to be old stock if you can find a trusted source or there going to be pulls.
PE4312 is a drop in replacement and still in production.

Thanks for that info . Mine were listed as new , but you never know from China . Hopefully they'll be NOS . After watching the video I really only want to have to go through this process once