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A diode is a good start. ?
But Q13 and R141 can exceed dissipation limits even when running at 12v,
If running off a fully charged lead-acid battery at 14v you will be severely stressing those parts.

I think an LM2940 between your power supply and the main Bitx40 12v power connection would be ideal. ?
Unlike the older LM7812, the LM2940 will provide reverse battery protection (just like a diode).
It will also protect Q13 and R141 from an incoming supply that exceeds 12v.

Power to the IRF510 doesn't need protection from a couple extra volts on the power supply
like that,?but could use protection from too much drain current. ? Perhaps just a 3A fast blow fuse.
Better yet, a current sense circuit that grounds out the gate bias voltage when it sees trouble:
? ?
Another plan is to have a dozen spare IRF510's on hand, they're quite cheap.

I'll defer to John and the others here on how to avoid clipping on that IRF510
and how much of a problem it might be. ?Not something I have fully figured out. ?
But my suspicion is that with only 100ma of quiescent drain current through the IRF510,
it will have to have high side drain current peaks of an Amp or two in order to generate 20 Watts of RF.
And since drive into the gate is AC coupled from Q14 and thus driving the IRF510
symetricaly about the quiescent gate voltage, it will spend an awful lot of time
with drain current at zero when it sees the incoming low going peaks.
However, most of that distortion would be harmonics of the transmit frequency,
and easily filtered by the LPF.

Has anyone success in using the BitX 40 for JT-65?
Ted WD4CAV

Jerry has some good ideas but the easiest solution to
clipping is to slightly increase the drain voltage. Assuming the
same drive level.

Most likely, clipping will occur on the higher frequency peaks (if it does).
The level at which clipping begins is more or less controlled by the IF bandwidth, i.e.,
the xtal filter bandwidth -- the more highs that get through, the more likely it is that
there is clipping. If it occurs on only an occasional high, it can usually be ignored. If
it is more often, it will have to be addressed.

The simplest solution is to increase the drain voltage to 28v or 30v.
That allows a greater excursion of the signal in the final. The IRF510
is a 70v device; I would not try to get much beyond 60v Pk-Pk of signal
out of it. Alternatively, you can get rid of the distortion in the LPF, but it is
much more work and figuring to do it that way. Mind you, the LPF still has to
handle the power you put through it, no matter what.

Yes, you will require a heat sink. The heat transfer derating coefficient is about
.30 degrees C per watt! The maximum allowed difference between the junction
and ambient temperature is 3.5 degrees C per watt. That means that at 10W output
the maximum temperature difference between the very small chip center and ambient
is 35 degrees! You probably cannot get too big a heat sink if you are using the device
for AM or SSB. Something like an Intel cpu heat sink or a large sink for a voltage converter
works well. (And the cpu sink gives you a fan as well! Hi.)

And use a good transfer grease between the tab and sink. It isn't rocket science.
Just think about how to get rid of a lot of heat generation; it will come to you.

john
AD5YE

The rig draws around 150ma, so regulating down from 24 to 12v that 7812 would be dissipating 2 Watts.
Could be made to work, but will need a heat sink. ?I'd go with two supplies.

Or maybe a boost switcher that turns on only when transmitting when you need more power than 12v gives
? ??
I have no idea if that thing works, or if there is an easy way to enable/disable it.

Or have two 12v batteries, normally operated in parallel, run in series to drive the PA at elevated power,
main rig continues to run only off the bottom battery.

Having at least a diode on the main power into the board is not a bad idea to give reverse power protection.

On heatsink for the IRF510, just go big. ?Very poor thermal transfer from die to TO220 tab on those guys,
so we want to keep the tab as cool as we can. ?/g/BITX20/message/22597

I haven't tried running mine at over 12v yet, haven't had time to play with it.
Most folks here running at 24v seem to be leaving the bias set at 100ma,
but that has to be clipping the bottoms off the transmitted output, to be dealt with by the transmit LPF.
Though if it's clean enough, then that's the way to go as otherwise you are burning more power
in the IRF510, potentially zapping it with heat. ?Would be interesting to check the IRF510 for linearity?
when operating at 24v and 100ma of bias. ? And the transmissions for meeting legal requirements.

Best solution would be to steal the push-pull amp?
from the uBitx, as neither IRF510 there is drawing much current until you start shouting into that mike.
? ??/g/BITX20/message/33255

Jerry, KE7ER

You're welcome, Brent.

My anti-chunk (eventually) was an adaptation of I7SWX's. All-transistor. FETs are not essential for that - might be for AGC, but haven't got to that yet. Might even be able to use the clamp for both! I put a k or 2 (6.8 actually, just what was to hand and small enough) between clamp and amp - evidently reduces low-level hiss. I also put a delay on PTT release - just a few milliseconds, but cuts the Tx->Rx chunk.

73

Dex, ZL2DEX

OK gang

I want to try to run the PA off 24 volts. Any suggestions as to size or type of heatsink.
Do I have to re-adjust the bias, etc?

I was wondering if anyone has used a 7812 to regulate power to the main board, or is it better to use 2 supplies?

The radio is working very well, with multiple contacts on both cw and ssb over the last week.?

73
Brent

Thanks Dex

Looks easy enough. That's what I love about this radio, it's inexpensive enough that you don't mind experimenting. I built the anti chunk circuit shown elsewhere here, that uses a 2n3906 to the ptt, driving a 2n7000, which shorts the lm386 input on ptt closure. I have it working well, but I did have to put a .02 (I think...was from the junk box) between the pot wiper and ground. I no longer get the thunder clap effect in the headset when I key the rig.

73
Brent, VE3CUS

I got my Bitx40 kit in the 10 days from India to the Caribbean, got it a couple days ago.

Need to assess which housing to use b4 building
--
AncelB, MIT EE6002

You will get a shipping confirmation from DHL
takes a couple of weeks for that to show up in your email.
I paid with Paypal

On Sat, Oct 7, 2017 at 5:23 AM, Dave James via Groups.Io
<gpodave@...> wrote:

Hello group,

I ordered the Bitx 40 with DHL delivery on the 29th September from the
RFSigs web page. Other than the paypal receipt for the payment I've had no
comms. I've written to teamhfsigs@... and have had no response. Is
this normal or should I be worried? The web order page promises delivery in
1 week with tracking.

Apologies if this is the wrong forum to query this but my order seems to
have dropped into a black hole.

73,

Dave, G8XUL

No, Brent, no AGC yet (no Raduino yet- it's en route), but Yes - lift R111(restores proper power switching to Q16) and 1N400x +12 (nearest I found was at R101, nearer end) to U1 pin 6. No ill effects as far as I can tell. Done as attempt? at reducing Rx-Tx-Rx 'clunks', and no ill effects. Attempt was unsuccessful but I left it at that anyway.

I agree Mac, I usually expect a couple of days before anything ships and then the shipping time in addition to that. So I really have no worries with this order.? Glad to see Dave got some info on his.? Just checked mine and it has shipped also.? Looks like I'll have a something new on the bench real soon.? 73 - Pat W4PBJ

Thanks guys, I've just had a notification and tracking number.? My BtX is in Frankfurt :-)

73
Dave (G8XUL)

I think,there is no serious problem. 29-1st oct it was weekend. Somebody has to check order, pack TRX, send it.

It is nor a big proffesional shop neither factory. Sometimes there is no "one day - ready to send" bitx.

But I agree, some kind of confirmation would be nice.

MAc
sp9mrn

PS I receive mine after 3 weeks (ordinary post, not DHL).

Pat,? thanks.? Good to know I'm not the only one (sorry that's at your expense :-).? If that's the case fine.? I know that this is a hobby and a very good price so an 'out of office' reply would be OK.? I was just worried that something had gone astray.??

73,
Dave

I don't know that it's normal, but you're not alone. I placed my order on 1 October and haven't heard anything yet either. No additional info in my paypal transaction either.? Perhaps someone was tied up this week?? Maybe parts are backordered (I'm waiting on parts for my RS-HFIQ that aren't due until April 2018)?? ?Good Luck - Pat, W4PBJ

Brent, thanks for taking the time to reply.? That gives me some useful info - nothing in the paypal records however.

73
Dave, G8XUL

I concur. I did some research on these things a little while ago. The AC ones use triacs, and they won't work with DC. Some of them won't even work properly with an inductive AC load. I'm guessing that board is designed to allow the arduino to control lights, appliances, etc.

73
Brent, VE3CUS

Should be power connection.? Arrrr, I hate how unnoticed auto correct makes me look illiterate.