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Messages - Kage

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1
Not sure where I saw the schematic but there was one someone made showing it was possible
to get around 5W(?) out on the low side of the FM broadcast band. Can't remember if it was the
IRF510 but it was in that ballpark. I'm sure the efficiency would be laughable but possibly still
useful.

I'd think the gate capacitance would become so high that they would be useless in the lower VHF
range but I've never actually tried to see the limits.

Seems there are hams who use them in the 6m band so if they can do 50MHz that begs the question
where will the maximum usable frequency of amplification become basically unity gain (if I should
call it that), or useful amount of amplification before it's useless?

2
One idea I had when building the old tried and true 3 IC MW PLL using the 4046 was its potential use to cover up into HF by using the modern TI versions that are good for up to around 14MHz and adding a second 40103 for further DIP switch division.
If using the circuit to drive push-pull it should be good to 7MHz but this is just a theory in my head, and honestly setting that many DIP switches
to get on frequency would be a pain and really only useful for 10kHz spacing unless using single ended in which case I suppose it's possible to use
5kHz spacing.
All that should be required is tying the 8-bit binary counter 40103 to another to get to 16-bit, and using the latest 74xx.. series ICs that support those higher frequencies since the original 4046 was really only good up to a few MHz as I recall.

Either way that old 3 chip solution for making a mediumwave synthesizer still runs rock solid in a few designs I've made over the years and it doesn't get much simpler for using classic ICs. Shouldn't be too hard to scale up to the HF band if one is willing to experiment. You'll only get 5v logic outputs from the latest though so either the designer has to use a gate driver IC or one of the more special mosfets that can be directly driven at that level which most will crap out at driving higher frequencies from gate capacitance. It's usually recommended to use a gate driver IC anyway though in these sort of designs.

3
The RF Workbench / Re: Distance with 10W on A.M. (M.W.)
« on: February 13, 2024, 2019 UTC »
I prefer top loading with a coil or even a combo of that and a T top hat or inverted L configuration, inductor at the 90 degree bend. Only drawback is the added top weight and the coil being much higher inductance compared to having it near the bottom tuning section when using a shortened antenna. Also getting the inductor turns right can be a pain since you have to take down and put up the contraption until it's tuned. This can be used as a single vertical antenna this way without needing to tie off wires at the top to a structure if desired.

When I've tried this I notice a considerable improvement with broadcast coverage compared to bottom loading. Has something to do with current distribution in the antenna but haven't had my coffee yet.
As Charlie_Dont_Surf recommended though your standard shortened T antenna (or capacity hat) just "works" and is even used down in the longwave band where shortened antennas are a must.

Of course getting as many radials down is the other functional section of the antenna and is equally important. Bare minimal tie to any large metal items earthed and experiment with that if you don't have the space or wire to put down over the ground.

It still amazes me how much people can pinch out of those pea shooter part 15 setups too. You'd think at some point there would be diminishing results but I guess sometimes every little thing in the overall antenna system does add up  8)

4
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 :D

Protection diodes installed. All is buttoned up and ready to listen to pirates again  8)

5
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!  8)
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!

6
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.

7
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.

8
Strong signal here WI, just hearing SSTV at 00:42 but sadly away from my computer with the decoding software

9
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 ;D

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.

10
"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

11
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  :o

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.

12
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.

13
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.

14
That would have been me. Cool, happy to get a listener. The last song was Maggot Brain. 25 watts carrier and homebuilt audio processing.

15
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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