Messages

1

Equipment / Re: Tecsun PL-880 AM BC band died sudderly and found out why

« on: October 24, 2023, 2230 UTC »

Not pretty but it works...



Don't mind the triangle electrical tape, I explain that in the video. It's just an external connection I soldered in that has nothing to do with the failure.
SMD transistor looks hilarious being turned 45 degrees upside down, but got to do what you can when the pinout isn't the same as the OEM part

Protection diodes installed. All is buttoned up and ready to listen to pirates again 

2

Equipment / Re: Tecsun PL-880 AM BC band died sudderly and found out why

« on: October 23, 2023, 1539 UTC »

So I've been thinking about this a bit more...

Since M R I and East Troy Don mentioned the Sony ICF-2010 radio I decided to pull the schematic up on that and sure enough
it uses a circuit which is very close to the one used in the Tecsun for the front end MW/LW transistor which is a 2SK152
in that radio.

This has me thinking if I can find a 2SK152 I would bet it would perform similar to the BF510 and there is some
wiggle room in the PL-880 to solder it in on nearby joints if careful to preserve the original SMD PCB pads in case I find
an original replacement.
The figures of both FETs are close from what I can tell.

Interestingly the SK152 datasheet talks about it being useful in head amplifiers for video cameras or VTRs but no
mention of RF applications. I guess they are a bit like jelly bean parts as long as specifications are right.
On the other hand I've tried a handful of other FETs I thought would perform good as a drop in yielding various
results from bad to mediocre but nothing that compares to the original performance.

If all else fails I may just button up the radio for now with a high gain bipolar with a bias resistor and
base capacitor in place of the FET which seems to perform almost as good but it's an annoying hack/workaround.

On a side note it appears Linear Systems is now producing a replacement for the discontinued BF510 called the
LSBF510 so that may be useful information for those in the same boat with me down the road...
https://www.prnewswire.com/news-releases/linear-systems-releases-replacement-for-discontinued-nxpphilips-bf510-n-channel-jfet-switch-301498152.html


UPDATE:
I found a SMD 2SK932 in an old Pioneer car stereo "Super Tuner" AM front end that isn't pin for pin compatible but can be fitted in and now the radios MW/LW is alive again and working as good as it did new with the BF510! 
Or possibly even better?.. because of the higher forward transfer admittance Yfs rating which is a head scratcher.
Definitely soldering in protection diodes this time so hopefully this doesn't become an issue *again*.
Also I remade the video and replaced it in the link above because the old one had a lot of mistakes I made.

Whew!

3

Equipment / Re: Tecsun PL-880 AM BC band died sudderly and found out why

« on: October 20, 2023, 2311 UTC »

Well it happened AGAIN!

Even after replacing the FET with another temporary part that was "good enough" I still managed to fry the input and you know what I narrowed it down to?...

Lack of back to back protection diodes on the built in antenna so that it could limit how much was going into the first stage transistor.
I tried to describe this in this video.

I re-edited my video and uploaded a newer version without so many mistakes...
https://www.youtube.com/watch?v=-2q8uIG3XK0

I'm to the point where I am testing ideas to replace the FET altogether with a BJT and so far it's working.
I do realize I can simply replace the FET with an equivalent "new part" and that will remain an option (if one can be found) but for now I just want the thing to hear stations on MW and this simple change that only increases the part count by 2 components (capacitor, resistor) not only completely replaces the FET but handles huge RF fields far better without distortion much like my DX398/ATS909 but still has the sensitivity to compare. I damn near feel like they should have used a BJT in the first place or at least spent a few more cents on protection diodes.

4

General Radio Discussion / Re: Tour of AM Stereo Station KYET

« on: September 08, 2022, 1432 UTC »

Awesome seeing Shango mentioned on here. By far one of my favorite youtubers and definitely recommend his channel.

5

North American Shortwave Pirate / Re: UNID 4185 USB 0030 UTC 20 MAR 2022

« on: March 20, 2022, 0042 UTC »

Strong signal here WI, just hearing SSTV at 00:42 but sadly away from my computer with the decoding software

6

North American Shortwave Pirate / Re: X-FM 4185 AM 0002 UTC 1 NOV 2021

« on: November 01, 2021, 0032 UTC »

Listening to the shoutouts 0030 UTC. Just tuned in and booming signal into Wisconsin as usual for X-FM on the Tecsun 880.
Nice wideband audio and have my radio bandwidth set for 9kHz. Almost sounds like an FM broadcast, can't even tell it's AM mode heh.

Thanks X-FM for the show! Enjoyed the shoutout.. and at the end of your show too

0238 Stripped - Depeche Mode, good song to end my evening with while in the radio room here.
0242 Off air.

I really hope someone recorded your show tonight and uploads it. The one time I don't have my recording device plugged into my radio go figure lol.

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North American Shortwave Pirate / Re: WDOG 6930 USB 2347 UTC 31 October 2021

« on: November 01, 2021, 0004 UTC »

"This is WDOG" "please stand by?" ID at 0000 UTC
Good signal here on the Tecsun 880, definitely strong and well above the local noise

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Equipment / Tecsun PL-880 AM BC band died sudderly and found out why

« on: August 18, 2021, 2243 UTC »

Just a tip for anyone who owns this radio and suddenly AM stopped working.
The symptom is kind of odd, FM and shortwave all work fine but going to AM results
in loud static with no stations picking up unless you have a transmitter right next to the radio.

Opened it up and nothing obvious looked wrong so I start injecting a 800kHz signal from my generator
into various areas and found the first stage AM antenna amplifier seems to be weak or dead.
To confirm it I check on the scope at the Drain of Q26 while injecting a signal into its Gate.
The waveform looked fishy and didn't seem to be amplifying as much as it should.

So after much headache I unsoldered the smaller than rice sized SMD component which is a BF510 n-type FET.
Digging around in my part box I found a through hole 2SK161 which at least has the same pinout even if it's 8x
the size of the SMD part!
Matched pin for pin touching the board by hand and the BCB came back alive.

I ended up soldering it in place bent over for now. The sensitivity is not as good as it was with the original
transistor so I need to find a legit replacement but have no idea where to look that won't cost much.
Only other idea is to replace it with a part that has close to the same specs 
With any luck maybe I will find a better part than stock and actually increase original performance but that
would be a crazy hack that would deserve its own post.

As to how the transistor died is a complete mystery. The radio was fine one day, then dead the next. I did not have it
plugged into an outdoor antenna. The gate and source of the FET are in parallel with the loop stick inductor so
how on earth the ferrite antenna could have generated a big enough pulse to fry the FETs gate is beyond me!
If I didn't know better I'd say the front-end got cooked by sitting under a broadcast antenna, but no
it wasn't from me 

I will say one thing that was odd is that this happened while I was camping out by a river with no houses around or stations.
While out there right before the AM died I was hearing some really strange wooshing click sounds which my friend found
strange sounding. It was strong sounding interference. Wonder if something was out there that fried my radio!? 
Probably just a coincidence.

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General Radio Discussion / Re: The HFUnderground.com chat is moving to Discord.

« on: July 23, 2021, 0258 UTC »

Awesome!

I always have discord pulled up on one of my two monitors on my dual monitor setup so that is very convenient to read the newest messages without having to purposely pull up rocketchat.

Might be a pain for people with old computers but anything recent should run it fine, even if using discord in your browser instead of its native software.

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North American MW Pirate Radio / Re: UNID 1710 AM 1055 UTC 14 April 2021

« on: April 14, 2021, 1340 UTC »

BTW I haven't been on the air in almost a year, so whatever that other station is, it wasn't me. But your report was definitely me.

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North American MW Pirate Radio / Re: UNID 1710 AM 1055 UTC 14 April 2021

« on: April 14, 2021, 1336 UTC »

That would have been me. Cool, happy to get a listener. The last song was Maggot Brain. 25 watts carrier and homebuilt audio processing.

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North American Shortwave Pirate / Re: WEZL 6927 usb 2149 utc 7 mar 2021

« on: March 07, 2021, 2233 UTC »

ID at 22:30, talk about using some new equipment.
Decent signal into south WI on my Tecsun 880 well above the noise.
Been a while since I tuned in pirates this early in the day. Good timing going back to the radio room I guess.

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General Radio Discussion / Re: Fast food drive through frequencies

« on: September 27, 2020, 2123 UTC »

I wish the 30MHz segment was used more because my Anytone 5555n transceiver covers up 25.615 to 30.105 and I always wondered what would be up on those higher frequencies around my area.

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General Radio Discussion / Re: Fast food drive through frequencies

« on: September 26, 2020, 2024 UTC »

Get a Baofeng and you'll be on all their frequencies at the same time according to a ham, get a Baofeng and you can have access to all their frequencies according to a ham. Get a Baofeng and be lucky to be heard a few hundred feet away by a ham. Make some mashed potatoes and gravy and get yourself some ham.

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Part 15 AM and FM Station Operation / Re: Talking House Transmitter - some spectrum plots

« on: September 26, 2020, 1920 UTC »

Narrowing the bw will also give a slight increase in range, for those stations that can match that bw on rx.

I generally agree with this, but I think it has more to do with packing the audio tightly in that bandwidth than it does simply limiting bandwidth.
I've tried both extensively and found that bandwidth restriction alone doesn't seem to have a huge impact, or any that I can tell at all from practical distances. It does give feel good points though so you know you're not interfering with adjacent stations.

What does matter is really cramming the audio into, as you suggested, the bandwidth of the average radio. Placing the NRSC curve to put some punch out to 5kHz makes a ton of difference, beyond that it's up to the station, and my preference is to ride the bandwidth so that up to 5kHz there is strong presence on soft passages or limited audio range (voice), and push the 5-9.5kHz hard to the standard curve, then drop it with the brick wall after that to comply like the big sticks. That presence around 2-5kHz needs to have its own care though or else it will sound awful on music. Professional audio processors actually treat this range specially with analyzing circuitry (or software) so that voice has punch and music remains full and good, and it's an art.

Remember stories of hot audio processors of yesteryear damaging old radio station transmitters? Running tubes too hot or pounding the mod transformer until destruction? That is what gets loudness and to really get that you need 100% modulation peaks and 95-98% neg. Maybe that is what the talking house transmitter needs? Sounds like a fun project
Not even sure if the thing can do close to 100% positive, or asymmetrical peak riding even though Stereotool can try its hardest to provide it.