Topics

?- How high SWR before smoke?

Thomas "Trip" Carswell Jr
 

I just RX my uBITx and have in on bench. I would like to add SWR bridge inside case.
I have read that very high ref. power will blow fuse and/or finals. So, I would like to use
resistive bridge as the SWR indicator. If I recall, the max SWR from a resistive style
bridge is 2:1  (??).   Will the finals handle this ??
My uBITx is for the "trail" so don't want to be popin' fuses or finals while out.

Thoughts?

Trip - KT4WO 
trcarswell@...

Jerry Gaffke
 

Your uBitx will be fine with an SWR of 2:1.

Your primary concern is heat on those IRF510's.
A dead short might eventually cause the IRF510's to get too hot (as could operating digital modes continuously).
If that's a concern, monitor the IRF510 heatsinks with a finger, should not get uncomfortably hot.

If powering the IRF510's from something close to 12v, 
I seriously doubt it would blow due to overvoltage if the antenna were absent.

Lots of folks in the forum have tested the open antenna port thing.
The BNC panel mount connector that came with some of the uBitx kits is not machined to spec.
Center pin from your antenna coax may not connect well with the center pin of the panel mount connector.

Jerry, KE7ER


On Thu, Jul 5, 2018 at 11:37 am, <trcarswell@...> wrote:
I just RX my uBITx and have in on bench. I would like to add SWR bridge inside case.
I have read that very high ref. power will blow fuse and/or finals. So, I would like to use
resistive bridge as the SWR indicator. If I recall, the max SWR from a resistive style
bridge is 2:1  (??).   Will the finals handle this ??
My uBITx is for the "trail" so don't want to be popin' fuses or finals while out.

Thoughts?

Trip - KT4WO 
trcarswell@...

Thomas "Trip" Carswell Jr
 

Tnx Jerry,

I have a small fan that will be blowing on the 510 heatsinks,(via switch) so hope that will tame that beast.
And will be using SO-239 for ant.  I just want it as robust as can be before hitting the trail.
It will weigh more than I want, but hope it's worth it. And a heck cheaper than an 817!!

Tnx agn de Trip - KT4WO

Ralph Mowery
 

While not what you asked, but if you replace the output transistors to the RD16HHF1 that many are doing, the data sheet says a 20:1 SWR.  Plus you get the benefit of being able to directly ground the tabs to a heat sink.  Just be sure to swap the leads as two of them are reversed.


On Thu, Jul 5, 2018 at 3:28 PM, <trcarswell@...> wrote:
Tnx Jerry,

I have a small fan that will be blowing on the 510 heatsinks,(via switch) so hope that will tame that beast.
And will be using SO-239 for ant.  I just want it as robust as can be before hitting the trail.
It will weigh more than I want, but hope it's worth it. And a heck cheaper than an 817!!

Tnx agn de Trip - KT4WO


Thomas "Trip" Carswell Jr
 

On Thu, Jul 5, 2018 at 12:40 pm, Ralph Mowery wrote:
RD16HHF1
At 4.75 each(RFParts) I may just do that!! ... are they "direct" replacements ???
(other than pinout)
Trip - KT4WO

Arvo W0VRA
 

On Thu, Jul 5, 2018 at 11:37 am, <trcarswell@...> wrote:
I have read that very high ref. power will blow fuse and/or finals.
Well, before I added the fan to mine, I accidentally did a full 40 M WSPR transmission, about two minutes full blast digital, with no antenna connected.  The PA sinks got way, way hot, and somehow the IR510s survived.

Ralph Mowery
 

Look here for some info on the replacing of the parts.  RF parts does have a $ 20 minimum order and about a $ 8 or so shipping and handling. That is where I bought some a few months back.  I did do a few other modifications tothe uBitx in the power chain.  I am not planning on battery power ,so the current drain did not matter to me, I just wanted to get the power up to 5 or 10 watts on 10 meters to drive some transverters at a later time.





On Thu, Jul 5, 2018 at 3:45 PM, <trcarswell@...> wrote:
On Thu, Jul 5, 2018 at 12:40 pm, Ralph Mowery wrote:
RD16HHF1
At 4.75 each(RFParts) I may just do that!! ... are they "direct" replacements ???
(other than pinout)
Trip - KT4WO


Arvo W0VRA
 

On Thu, Jul 5, 2018 at 01:43 pm, Ralph Mowery wrote:
Look here for some info on the replacing of the parts.
I've heard that the v4 of the µB board has pads for the RD16HFF1s?  Has anyone posted something about swapping out or pictures of the board there?

Jerry Gaffke
 

The RD16HHF1's do have some advantages.
Primary advantage is that the tab is connected to the source, not the drain,
so you can heatsink them directly to the chassis if you wish without using any electrical isolation.
But an IRF510 on a properly done heatsink can dissipate about the same power.

They are capable of more power out at 12v than the IRF510's, but you would have
to rewind some transformers to take advantage of that.

Others here will have other points to make.
For example, when operating at 12v the RD16HHF response might be a bit more linear.
Though if you are worried about spurious emissions the FET choice is not much of a factor here.

I doubt they would be any more robust than the IRF510's.
And I doubt it's worth the trouble.
On the other hand, could be fun to try.

> if you replace the output transistors to the RD16HHF1 that many are doing, the data sheet says a 20:1 SWR. 

Many here have demonstrated that the IRF510's are capable of dealing with much higher SWR's than 20:1.
No antenna connected means infinite SWR.
And the RD16HHF1 will have the same trouble getting heat transferred from die to tab that the IRF510 does.

Jerry


On Thu, Jul 5, 2018 at 12:45 pm, <trcarswell@...> wrote:
On Thu, Jul 5, 2018 at 12:40 pm, Ralph Mowery wrote:
RD16HHF1
At 4.75 each(RFParts) I may just do that!! ... are they "direct" replacements ???
(other than pinout)
Trip - KT4WO

ajparent1/KB1GMX
 

I'd keep any radio under 2:1 for extended period of time.  I also abuse that often
so far no fried finals.

However I did some testing today and the cable was on the floor so for 5 minutes
RF now power measured, oops.  Finals were barely warm and still happy.

The max temp for the part is 150C however that pushing things and its the
temperature of the hottest part of the die.  Hint water boils at 100C.  Keep
the finals under 70C and you should be good for heat.

The usual problem is there are resistive and reactive parts to a poor SWR and
the reactive part can drive the amp into oscillation and it will self destruct very fast
doing that.  The reason this is so is the Low pass filter is often not the frequency
it self oscillates at and the finals have DC power on them during RX if the are well
and fully oscillating they have power and an open antenna relay.  Bad situation.

Both IRF510 and the RD16HHF are subject to failure if the amp as a whole is not stable.
Ads claiming of infinite  SWR often do not count heating and other possible abuses
heaped on at the same time.  

Most resistive bridges unless pure crap are a 50 ohm load and can vary some
but not 2:1.  The crappy ones can go as far as 25 to 100 ohms (2:1).

FYI 2:1 is not high!   

What you are asking is how do I make my radio bullet proof and testing at home
is a starting point.  If you can't fry the finals there then likely it will work elsewhere.

Allison

Walter Keen
 

For a backpacking radio, as I'm hoping to use my ubitx v3 for, can anyone see reasons to not move to RD16HHF1's or similar, particularly in my case for the reason that a larger passive heatsink out of my parts bin is slightly better to plan for in terms of battery power (weight vs space) , vs a fan or two running on the IRF510's


On Thu, Jul 5, 2018, 2:41 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
The RD16HHF1's do have some advantages.
Primary advantage is that the tab is connected to the source, not the drain,
so you can heatsink them directly to the chassis if you wish without using any electrical isolation.
But an IRF510 on a properly done heatsink can dissipate about the same power.

They are capable of more power out at 12v than the IRF510's, but you would have
to rewind some transformers to take advantage of that.

Others here will have other points to make.
For example, when operating at 12v the RD16HHF response might be a bit more linear.
Though if you are worried about spurious emissions the FET choice is not much of a factor here.

I doubt they would be any more robust than the IRF510's.
And I doubt it's worth the trouble.
On the other hand, could be fun to try.

> if you replace the output transistors to the RD16HHF1 that many are doing, the data sheet says a 20:1 SWR. 

Many here have demonstrated that the IRF510's are capable of dealing with much higher SWR's than 20:1.
No antenna connected means infinite SWR.
And the RD16HHF1 will have the same trouble getting heat transferred from die to tab that the IRF510 does.

Jerry

On Thu, Jul 5, 2018 at 12:45 pm, <trcarswell@...> wrote:
On Thu, Jul 5, 2018 at 12:40 pm, Ralph Mowery wrote:
RD16HHF1
At 4.75 each(RFParts) I may just do that!! ... are they "direct" replacements ???
(other than pinout)
Trip - KT4WO

John (vk2eta)
 

Hello Walter,

If you can/want to use batteries that are higher than around 14V I would not recommend the RD16s. 

Speaking from personnel experience I managed to kill an RD16HHF1 when I forgot to reduce the voltage from a lithium 4S battery.

I have a switch to bypass 3 diodes to reduce the maximum voltage from 16.8 to under 15V for the PA.

They survived at low SWR but gave up when tuning as the SWR went up to 9+.

The advantage of the IRF510 is that even at 16V they produce a lot more power than at 12V.

So far I have not managed to kill the IRFs and I will stay with these for my portable rig.

73, John

Jerry Gaffke
 

Google "TO-220 insulator kit".  You can steal them from old equipment such as a computer power supply.
With two of those and some heat transfer grease, you can mount the IRF510's to one grounded heatsink.
The RD16HHF1's don't need the insulator kit, since the tab is the source pin, and gets grounded anyway.
But the insulator kits work well with the IRF510's.


On Thu, Jul 5, 2018 at 09:16 pm, Walter Keen wrote:
For a backpacking radio, as I'm hoping to use my ubitx v3 for, can anyone see reasons to not move to RD16HHF1's or similar, particularly in my case for the reason that a larger passive heatsink out of my parts bin is slightly better to plan for in terms of battery power (weight vs space) , vs a fan or two running on the IRF510's

Ralph Mowery
 


I understand full well about how to isolate the irf510s electrically.  However has anyone given any thought as to what may happen, if anything, to the RF coupling if the transistors are mounted on the same heat sink ? 

On Fri, Jul 6, 2018 at 10:24 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Google "TO-220 insulator kit".  You can steal them from old equipment such as a computer power supply.
With two of those and some heat transfer grease, you can mount the IRF510's to one grounded heatsink.
The RD16HHF1's don't need the insulator kit, since the tab is the source pin, and gets grounded anyway.
But the insulator kits work well with the IRF510's.

t/ BITX Web Site of Mike ZL1AXG
https://groups.io/g/BITX20/wiki/home Wiki

Jerry Gaffke
 

Should be fine, gets done all the time.
The drains are operating into a very low impedance, driving the antenna through that step-up transformer.
A little added capacitance there is not terribly significant.
The fact that they are mounted on the same heatsink is not an issue,
generally the heatsink is bolted directly to the chassis and is at RF ground.

Other than no need for heat sink insulators, the other big advantage of the RD16HHF1's
is a somewhat lower gate capacitance, so easier to drive when operating above 20 meters.
But the RD16HHF1's are no panacea, we have bigger problems with the uBitx's gain
through all those 2n3904's than we do with the IRF510's.
And unless you have a cure for Allison's  45mhz-DialFreq  spur,
    https://groups.io/g/BITX20/message/52838
you should be operating at low power for 21mhz and higher anyways.
If at all.

Another big advantage for some is that RD16HHF1's are "Real RF" parts, don't want
their rig soiled by some fool switching FET designed for use in automotive turn signal blinkers. 
If that's an issue for you, by all means go for it.   
But the IRF510's work just fine.

If you are worried about damage from high SWR or high Vcc, the IRF510's are the better choice.
Their max Vds is 100v instead of the wimpy 50v Vds max spec of the RD16HHF1's.

Jerry
 


On Fri, Jul 6, 2018 at 07:42 am, Ralph Mowery wrote:
I understand full well about how to isolate the irf510s electrically.  However has anyone given any thought as to what may happen, if anything, to the RF coupling if the transistors are mounted on the same heat sink ? 
 

ajparent1/KB1GMX
 

Yes< RD16s are speced for 12V nominal nd16V max.  Its not wimpy but specifically
designed for 12V RF systems.   

IRF510 is speced for 100V, max 4A @100C and is a very robust device given half a chance.
So its seemingly hard to fry.

BOTH devices will disappear if the voltages to the gate (RF or DC) exceed a safe value
like 12V for the RD16 and 20V for the IRF510.  THis can happen if the amp is unstable
and oscillates, due to Miller feedback (gate to drain capacitance) if there is a large
RF voltage on the drain and the circuit is not RF stable the coupling can be sufficient
bring the gate over the breakdown rating.  All mosfets have this limit, I've fried
MRF137s that way and exotic GaN mosfets too.

The fact that the RD16 tab is ground is handy... BUT at RF where you ground things
can be precarious as you can create incidental current loops that incite instability.
Please remember there is no such thing as ground only the circuit common
return point for currents.  If you ground the board and the tabs of the RD16HHF
you created a set of current paths that Farhan has no design participation in and 
may or may not be stable, likely the latter.

I run IRF510s a pair push pull in an amp at 28V and they do about 55W at 40 or 20M
and have done so for more than a decade.  24-30V range is a sweet spot for these.
Its suffered shorted coax, open coax, no coax and wrong TX filter switched in
without failure.  I will point out the power supply used inside that amp has a current
foldback at 4A, hint 4A at 28V is 112W input to the amp and its trying to put out
60+ watts at 40M.

I've also paralleled 8 IRF510s as 4x4 push pull to make a 200W+ 6M amp.  Runs best
at 28-30V for SWR resistance and max power at 36V was near 275W.  They are
decently good IMD at 28V not exceptional but in the range of as good as commercially
made VHF radios..  Seems to tolerate most abuses well so far.  At 28V it wants a 16A
(500W switch mode power supply) supply minimum and the devices are peaking
about 4A each!

I've used RF16HHF at 20W max because the are 12V use where the IRF510 is not quite as good
for IMD.    I have not found them to be fragile but not quite as rugged as the 510.

Both parts will self destruct if the amplifier is not stable.  This means either part.
It happens faster than a fuse.

With all that said....

Just worked on someone else's uBITX that had a problem on 40M, it produces half the
power as 80M (15W) or 20m!(10W)  Reason was the output PI filter has coils that were
mis-wound (wrong inductance).  Easy fix once discovered....  Why relevant  here? 
The amp was putting 11W into the filter and getting 5W out.... That means the reflected
power the amp was seeing was 6W  That is an SWR well over 6:1 and the finals were
happy and never failed.

High "SWR" rarely kills finals its often instability with reactive loads.  Overheating, over
voltage and over current can.    Believe it or not those are the same things that can kill
the venerable 6146! 

Allison

ajparent1/KB1GMX
 

Ralph,

Calculate the capacitance of the transistor tab to heatsink with a .002 think mica insulator.
Do that first.  For both.

Now ground the heatsink to the board ground.  Not an issue.

Don't forget the RD16HHF uses the same package so it has about 4nh of lead and
bond wire inductance.  That means the tab and the enad connection point at NOT
at the same RF potential.  Ground the tab and the heatsink is now carrying RF current.

The RF coupling is already there via the output transformer.  

Allison

twmitchell.g3lmx
 





Sent from Samsung tablet.

-------- Original message --------
From: "Jerry Gaffke via Groups.Io" <jgaffke@...>
Date: 06/07/2018 15:24 (GMT+00:00)
To: BITX20@groups.io
Subject: Re: [BITX20] ?- How high SWR before smoke?

Google "TO-220 insulator kit".  You can steal them from old equipment such as a computer power supply.
With two of those and some heat transfer grease, you can mount the IRF510's to one grounded heatsink.
The RD16HHF1's don't need the insulator kit, since the tab is the source pin, and gets grounded anyway.
But the insulator kits work well with the IRF510's.


On Thu, Jul 5, 2018 at 09:16 pm, Walter Keen wrote:
For a backpacking radio, as I'm hoping to use my ubitx v3 for, can anyone see reasons to not move to RD16HHF1's or similar, particularly in my case for the reason that a larger passive heatsink out of my parts bin is slightly better to plan for in terms of battery power (weight vs space) , vs a fan or two running on the IRF510's

MVS Sarma
 

Hats off Allison for a nice treat in this poat . Messages are crisp and digestible. Many thanks

Regards
 vu3zmv