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Old 24th Feb 2017, 9:28 pm   #21
Wendymott
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Default Re: 40 Metre SSB Transceiver.

Hi Tanuki... Only LSB I'm afraid....I have gone with convention, although the insertion oscillator is switchable for the multiband version... "coming soon".
The front panel was made using my PCB package, printed onto white card.....then one sheet of my pcb printing acrylic to protect it.
Surprising.... no one commented on my "Huge" speeeeling mistake....It should be TRANSCEIVER of course.... but in mitigation I dont have a proof reader to hand. Next time eh ?
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Old 13th Mar 2017, 2:20 pm   #22
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Default Re: 40 Metre SSB Transceiver.

Hi Peeps... Just a quick question. I am building a Linear 100W PA... being driven by the item in this thread.
The output is 10W PEP, but I dont know if I should load the antenna terminal with a 50R when feeding the Linear. Surely the output stage will get upset if unloaded. The 100W module has no input load resistor, so I assume the suppliers think one is included in the driver. Your comments are welcome please.
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Old 13th Mar 2017, 5:09 pm   #23
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Default Re: 40 Metre SSB Transceiver.

Impedances at RF can get difficult to undestand.

If you buy say a 10W transmitter from one of the usual Japanese firms, the antenna output port will have an SO239 connector with "50 Ohms" written next to it.

It doesn't mean "I am 50 Ohms". It means "Please connect me to something that looks like 50 Ohms or else I shall sulk." If you measure the effective source impedance to this connector, it is unlikely to be 50 Ohms and there won't be a resistor inside setting it to whatever it happens to be.

If you buy a linear amp to go with it, it may well have "50 Ohms" written by the input connector, or else in the book of words. In this case it *does* mean "I try to look like 50 Ohms to whatever is driving me". Whoever designed the amp found the input impedance of the active devices and tried to transform it into 50 Ohms across the frequency range. Of course, they won't have succeeded perfectly, but they should have got as close as they could. Close enough for it to work usefully. In the amp, it might be an entirely lossless transformation if they are trying to conserve drive power and maximise gain, but there may be resistors or even an attenuator pad to tame parasitic oscillations and/or to present a nice impedance.

If you buy a posh sig gen, then do expect resistors to set and control the output impedance The output level control is usually (not always) calibrated to show what it will put into a good 50 Ohm load.

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Old 13th Mar 2017, 10:54 pm   #24
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Default Re: 40 Metre SSB Transceiver.

Hi David. The input to the PA Module is a "Pi" resistor arrangement 300R to deck then 20R in series then another 300R to deck.. a 3dB atten.... see attached..... But I am sure the resistors will not survive 10W... I know I can back off the drive, with the mic gain control....
Its just that the O/p circuit of the exciter....I dont want to damage it.
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File Type: pdf RF_AMP_2078_SCH_V306.pdf (23.1 KB, 84 views)
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Old 14th Mar 2017, 12:18 am   #25
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Default Re: 40 Metre SSB Transceiver.

If it's a 3dB pad and you're putting 10W in, then 5W is coming out as heat.

The output voltage will be 0.707etc that of the input, so the power dissipated in the output resistor will be half that in the input. So it's the input resistor which needs to be beefiest.

The pad does nice things for the stability of the power amp and stops interactions between the amp and the exciter.

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Old 14th Mar 2017, 3:49 am   #26
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Default Re: 40 Metre SSB Transceiver.

To your original question of needing a 50r resistor across the antenna terminal, no, you don't need one, that input attenuator on the PA will look like 50r to the transmitter (actually 51.997r or thereabouts).

As David says, more importantly, are the attenuator resistor sizes (Watts) large enough to handle the 10w input?

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Old 14th Mar 2017, 11:24 am   #27
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Default Re: 40 Metre SSB Transceiver.

Hi David and Terry....... It WILL BE.........I will re engineer it....The thing is....10W is Peak.. not average.. and unless you shout a lot.... unlike the "I1's" it should be ok....although I do like to "rag chew"..not these 10 second overs..

Just another thought... my PSU is set at 25V DC... thus 4A ish for 100W...the data sheet for the module states 13.8V DC for 9A ish....The data sheet for the IRF530 states 100V...VDS...I assume the 13.8V was for running from a car battery...
Hopefully it will be ok...... but your comments again would be gratefully received.
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Old 18th Mar 2017, 12:40 pm   #28
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Default Re: 40 Metre SSB Transceiver.

Wendy, just so I have all the marbles in the right order:-

Your transceiver puts out 10w.

The pdf you posted above for the PA - you are building that exactly or part thereof?

It's just that I noticed, according to the circuit, if you are building (or have that exact module), it only requires 100uW or 0.1mW drive.

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Old 18th Mar 2017, 3:31 pm   #29
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Default Re: 40 Metre SSB Transceiver.

Well done, looking forward to seeing the external RF Amp ( valves maybe ? )

de Jon
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Old 18th Mar 2017, 11:27 pm   #30
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Default Re: 40 Metre SSB Transceiver.

Hi Terry. and Jon. I decided that 13.5V @ 8 amps was not where I wanted to go, thus I upped the Supply to +24V... However as with all things, it did not go to plan, as the supply smoothing cap went "Bang"... only rated at 16V...When replaced... and NO RF input the driver was drawing 2A, even before I applied RF.... so I thought..... remove the pre drivers, and use another circuit I found using just 2 X IRF640's.
Its funny but, as we all know,, you change one thing.. and another problem arises. I want to use the RF output from the Exciter to switch the RF relays, but I had to amplify the "Non Modulated" rf to switch the change over relay,
I have taken a couple of days off from RF.... to make a new UV light source for pcb exposures.......... so I will report back soon.
No Jon.. sorry.. no glass in this...I dont want to go.. really high power, not like the "shouty" Italy Ones...
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Old 22nd Mar 2017, 5:21 pm   #31
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Default Re: 40 Metre SSB Transceiver.

Hi peeps a further update and questions, that I hope you can help with.
I reverted to 15V DC supply for the PA......and limited the PSU to 5A....... this would mean a DC input of 75W. Ok so far. With a non modulated RF input of 0.35V rf from my 2022, I was getting 90W into my RF load "50"R. Monitored with a Watson W220 power meter.
Looking at the O/P waveform it was obvious that the "Extra power" was attributed to harmonics and stuff , as... at this time the PA O/P was not filtered.
Adding a 3 pole bandpass filter from Mini kits, this made the O/p look a nice sinewave, but obviously reduced the RF output to 35W.
Increasing the RF drive from the 2022 to get the Relay switching sense transistor to switch the PA current went up to < 6A, and the PSU was "folding back" and the RF dropping to about 25W
I replaced the internal psu with a 10 A 15V supply.
As the PA Could now draw up to 10 A........ it soon started to runaway, and as far as I can see at least one of the Output devices has died.
The PA O/p devices are IRF640's....which are rated at 18A / 200V.
The heatsink insulating washers are those grey soft plastic / fabric types, with heatsink compound....... the heatsink was not getting hot, but if the insulating elements are wrong, the internal junction of the fets may not be cooling properly.
Now to the questions..What RF output can I expect / efficiency from the PA
and.... what suitable insulating washers should be used.
I have 3 X IRF640's left... but I dont want to kill anymore than is necessary.
I attach the PA schematic,
To note Q2 is taking about 0.5A @ 15V..
I now realise that the 100W claim for these modules is not based on our reality of Filtered 7 Mhz, but a measurement of everything including the kitchen sink.
Thanks for reading and maybe your comments
Attached Files
File Type: pdf RF_AMP_2078_SCH_V306.pdf (23.1 KB, 91 views)
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Old 23rd Mar 2017, 5:32 am   #32
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Default Re: 40 Metre SSB Transceiver.

The information I downloaded for that amp indicates it is only good for 45W (with IRF 530's).

Also to bear in mind, is that the gate capacitance of the '640 is about 3 x higher than the '530, which means different input matching is required.

And the output capacitance difference is higher by around 7x for the '640.

This alone will be causing you all sorts of grief if trying to use the component values as shown in the pdf (ultrasonic oscillation and instability being one possible cause of killing your MOSFETS).

Those 'insulating washers are those grey soft plastic / fabric types,' are silicon and should be fine.

Efficiency wise, I make it about 37% (but then maths was never my strong suite).

Personally, I'm not a fan of using these styles of MOSFET for RF amps, as, although there are plenty of designs using them on the 'net, what they don't tell you is how finicky they can be to make work in this type of application or how many they smoked getting the design to work.

Having said that, hopefully, there is a member on these forums who has successfully done this and will chime in with some more practical info for you.

Terry
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Old 23rd Mar 2017, 1:24 pm   #33
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Default Re: 40 Metre SSB Transceiver.

Hi Terry.... ALL comments well noted..... I will revert back to the IRF530's and see how it goes....Maths is also my Achilles heel...I often wished I could understand how it worked...but hey ho..Old dogs etc etc.
I will post when I get it working... As it happens the the Q2 pre driver also went faulty.. drawing 2A +, it measured ok DC wise "diode test" but a replacement put the current back to 0.5A.
Thats why I questioned the efficiency of the isolating washers...
Thanks for your comments.
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Old 24th Mar 2017, 12:30 am   #34
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Default Re: 40 Metre SSB Transceiver.

Quote:
Maths is also my Achilles heel
One of the reasons computers are so useful.

If you are worried about the insulating washers, clean them off and hold them up to the light to make sure they have not been pin-holed, not very common, but does happen.

Replied to your PM too.

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Old 24th Mar 2017, 2:41 pm   #35
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Default Re: 40 Metre SSB Transceiver.

Hi Terry Yes.. all noted.. the insul washers are ok... and I have removed the conducting grease..I replaced the IRF640's with 530's and I can squeeze 50W into a 50R load, but it does limit at .225V RF...input.... so something is not happening... as the supplier stated 100W. Ah well... thats suppliers and experimenting...I ordered another X10 IRF530's in case of more bangs... however the pcb pads are looking a bit sick now.
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Old 24th Mar 2017, 3:43 pm   #36
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Default Re: 40 Metre SSB Transceiver.

Quote:
Originally Posted by Skywave View Post
.... Apart from the appearance of the front panel, I am impressed
Hey Al, I like the front panel! even including the spelling of 'transceiver!' I agree that if it was any more honed, the whole unit would look bought instead of home-design-built.

Nice one indeed, Wendy!
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Old 24th Mar 2017, 5:06 pm   #37
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Default Re: 40 Metre SSB Transceiver.

Andrew2...... I just re read your reply to me on page one....ref your Topband Transceiver.. I wonder if you considered a SSD oscillator for the VFO, rock steady and with digital readout..... but I guess you like the Display you have already... just a thought.
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