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Hi

I'm reaching out to the experts for advice, guidance & help please.

The Hermes Lite 2, "HL2", is a DDC/DUC SDR transceiver - - which can output upto 5W PEP RF.

The RM Italy BLA-350 plus, "Linear", is a 400W PEP HF Linear amplifier - with an input drive of upto 10W.

At 5W RF out from the HL2, the BLA-350 puts out about 130W PEP.

So, the problem is how to get the output of the HL2 from 5W to 10W to drive the BLA-350 ?

The solution looks like it might be to use the QRP Labs 10W Linear Amplifier - - “PA”, to generate the 10W required to drive the BLA-350 to full power output.

The first step is to reduce the 5W HL2 output down to 25mW acceptable to the PA, a T attenuator giving about 25~26dB attenuation should reduce 5W to around 25mW. The T attenuator would comprise of 2 x 45 R in series with a tap to ground of 5.6R to yield an attenuation factor of -25.11dB - . The HL2 does have a 17dBm fixed output intended for transverter operations but one would still need to arrange for receive signal switching; the approach I've taken I think permits me to use the drive level in the HL2 to control the output power from the Linear.

During receive, the PA, and attenuator must be bypassed; during transmit, the receive chain needs to be bypassed, relays are used to carry out the required switching operation when PTT is closed /connected to ground by the HL2.

Hopefully the schematic below describes what I think needs doing with sufficient clarity.

I would really appreciate your advice, guidance, help, suggestions for improvements, and of course correct my errors.

Very Many Thanks, 73

Peter - GM8JCF

As outlined that is the way to go.

You may consider a low level PTT control for that so the keying voltages
for the amp and driver are compatible. also a way to shut down the
driver amp for a mid power solution.

--
Allison
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Thank U Allison, that was very quick off the mark, very much appreciated.

I have used relays for voltage free keying of the BLA-350 and for keying the QRPLabs 10W Linear as the most flexible and blow-up-resistant method,

The HL2 provides an OC keying output, and I currently use that to drive an opto-coupled relay to key the BLA-350, I know that most people just run the EXTTR connection from the HL2 into the PTT input of the BLA-350, but for the sake of approx USD 20 and a little soldering time, I prefer to have a fully isolated connection to protect my precious HL2 !!

Once again, thank you

Peter - GM8JCF

You're thinking about the right things. I would recommend a bit of testing before building a pyramid

?

First: I thought it was called 350 and output 300W peak on a very good day but I may be wrong

You say 5W in 130w out

and 10w in 400w out Again - I thought it was called 350 and output 300W but I may be wrong

Otherwise Are you sure its a Linear amplifier ? Are you sure you have 5W from the rig ? What does the RM input SWR look like ? Is this flat across all bands ?

?

It's also common for gain reduction (gain compression of the last few dBm of power ) to affect the higher output levels of such amps making the above scenarios even less likely

?

So first decide what power level gives you a signal you're prepared to attach your callsign to and check all the bands .

Then make up a test to see what the Rig output is and what the amp gain at your chosen output level is.

Your proposal does allow you to treat the 10w linear as a module but it has way more gain than needed and it is possible you could remove the first (BS170) stage and make or adapt the final stage input transformer for 50 ohm input. Nicer but optional Otherwise yes - lots of attenuation (amount tbc) but make sure the first stage of attenuation can take the 5W in and see if the attenuation actually needs to vary by band . . .

?

?

On Fri, Jul 12, 2024 at 02:13 PM, Bruce Akhurst wrote:

?On Fri, Jul 12, 2024 at 02:13 PM, Bruce Akhurst wrote:

First: I thought it was called 350 and output 300W peak on a very good day but I may be wrong

You say 5W in 130w out

and 10w in 400w out Again - I thought it was called 350 and output 300W but I may be wrong

Otherwise Are you sure its a Linear amplifier ? Are you sure you have 5W from the rig ? What does the RM input SWR look like ? Is this flat across all bands ?

Hi Bruce

Thank you for your comments, as far as I understand it, the BLA-350 is specified in RMS terms, eg the front panel power out meter is in RMS - Page 10 user manual "Analogue Power Meter (b) Displays the output power in Watts RMS.", (I didn't think that Watts RMS was a valid thing, but that's what the user manual says !), and the curves on page 12 of the user manual agree with what I see on the BLA-350 power meter, eg my Hansen FS-500H SWR & Peak reading Power Meter will show 100W when I set the HL2 for around 3W, but the BLA-350 power meter shows about 60~70W (on 60m) which is 100/1.4142 ~= 70.7, so if the curves on Page 12 are correct, then the BLA-350 can develop ~300W "RMS" ~= 400W PEP which is what other users of the BLA-350 have reported - eg = anyway, having warned me, I'll now set up some very carefully controlled tests, eg RF sampler, Oscilloscope, with my dummy load to find out the reality :-)

Your proposal does allow you to treat the 10w linear as a module but it has way more gain than needed and it is possible you could remove the first (BS170) stage and make or adapt the final stage input transformer for 50 ohm input. Nicer but optional Otherwise yes

I am by no stretch of the imagination an analogue engineer never mind an RF analogue engineer, so the idea of me messing/adjusting about with Hans' design is only going to end up with lots of smoke, disappointment and non-functionality. I can put 3 resistors together in a T/Pi pad but it's been way too long (+40 years ago) since I did any serious analogue electronic engineering. Also, I want/need to keep the QRPLabs 10W amplifier to it's standard build so that, a) I can ask for help, and people can help me because my version is not "special", b) if I need another one I can just get another standard QRPLabs 10W linear amp module c) I can easily adjust the attenuator to get the results I need, d) from what I've read on this forum front-ending the QRPLabs 10W linear amp with a resistive attenuator is a good thing to ensure better convergence towards 50ohm input impedance.

BTW, I'm using 3W metal oxide resistors for the T pad which should easily (famous last words) be able to absorb the 5W or so out fromn the HL2.

Thank you once again for taking the time to share your thoughts with me and trying to help me.

73

Peter - GM8JCF

What is the drive from the HL2 without the onboard PA activated? I know it is a very low level output but I don't remember if it is adjustable. You may not need a t attenuator if the output is sufficient.

Joshua

On Fri, Jul 12, 2024 at 04:11 PM, Joshua KJ7LVZ wrote:

What is the drive from the HL2 without the onboard PA activated? I know it is a very low level output but I don't remember if it is adjustable. You may not need a t attenuator if the output is sufficient.

Hi Joshua

When the HL2 onboard PA is not enabled, there is NO RF output on the ANT output connector, the ANT connector becomes a RX input connector, and the RF1 connector is the only RF output, 17dBm, from the HL2. RF1 is OUTPUT only so I would still need relay(s) to switch the antenna between RF1 for transmit and ANT for receive, and I'm not sure that RF1 is variable RF level (or indeed low pass filtered).




Thank you Joshua for taking the time to try and help me, really appreciated.

73

Peter - GM8JCf

On Fri, Jul 12, 2024 at 04:23 PM, G8JCF wrote:

The HL2 does have a 17dBm fixed output intended for transverter operations

Using this would be my approach, rather than attenuating the signal by 26dB and re-amplifying it by 29dB.
73, Don N2VGU

Linear Tech's AD8009 highspec VIdeo amp is your friend here - costs about 5 Benjamins each from Chicom dealers . THese have been successfully used as driversfor RD 15HH Mosfets in class A to get 7 W linear out. Will give up to 24.7 dBM LINEAR power into a 50R single ended load at 12 V supply, without sweating the silicon. that's 7.7 dBm over your start position.

For Filters, I'd consider just a Heist Two of Hans the genius's Qmx + two band filters to make up a four Pi topology set that would cover from 40-30-20-15 Mhz that does not need to be switched . It would be 50Z in 50 out ... anything outside there in frequency - why bother :-)) ??

Obviously 80 and 60m bands are implicitly covered in any case . Nothing new under the sun - if QrpLabs in Istambul have not done it , then the crows working for the CIA or NSA probably have.

Peter , before you jump in the company 60dbm.com out of Ukraine but still working has some nice solutions specifically set up for the machines like Hermes Light and even lower power Qrp transmitters . if you will accept 100W out then for 2-4mW in you have a high quality solution using modern components. These boards can be bought as modules or fully built up with auto frequency detection, heatsinking and most importantly a full set of LPFs. What they don't seem to have is high SWR shutdown. The basic board that goes in amp below costs $250 without heat sink and filters . if you used a splitter-combiner design you'd be looking at abt 180W out for 8mW in.

?

100 Watt HF/6m Power Amplifier for Yaesu FT-817, Icom IC-703/705, Elecraft KX3, automatic band switching

$399.00

Timmy,

Your not paying attention.
Refresh yourself with /g/QRPLabs/message/125855

He has a nice BLA-350 that with his 5W gives him 130W. It needs 10W for
full power (greater than 350W).

So far you have given a bunch of suggestions that does not get him
that 10W and a few that can barely do what he already has. So stop
polluting the topic with wild and inapplicable ideas.

The best suggestion is the 17dbm output from the HL2. I'd try that first
as its fairly close to the ideal. It avoids the high power attenuation.
Still needs switching but Peter understands that.

--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.

And here is another solution from EU1SW. Costly but offers 14-bit, 6m and 160m and power to run your amp to full output:

https://www.ebay.com/itm/256147932051
--
John AE5X

>>>Linear Tech's AD8009 highspec VIdeo amp is your friend here - costs about 5 Benjamins each from Chicom dealers . THese have been successfully used as driversfor RD 15HH Mosfets in class A to get 7 W linear out. Will give up to 24.7 dBM LINEAR power into a 50R single ended load at 12 V supply, without sweating the silicon. that's 7.7 dBm over your start position.<<<

Not useful at all for this application.

First he has 37dbm (5W) already from the HL2.? So there is no step up there as
24.7 DBM is 350mW and 7 W (using RD15) is still short of the 10W desired.
Plus a lot of construction to make it work.

Since he has 5W already its only +1.4db increase for that 7W.

So the QRPL amp with the HL2 17dBm output is a better match to the task.
If that ends up being too much drive a small low power (50mW) 2-4db
attenuation is far easier to do if needed.


--
Allison
------------------
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direct email will go to a bit bucket.

On Sat, Jul 13, 2024 at 08:45 AM, ajparent1/kb1gmx wrote:

a nice BLA-350 that with his 5W gives him 130W. It needs 10W for
full power (greater than 350W).

Again, the numbers do not add up. Unless the amplifier has a lot of gain expansion (compression is more likely) 10 W will only give 260W, far short of the desired 350-400W.
I suspect that something like 15+ watts is going to be needed, likely more if the gain compresses. I also suspect that 400W is going to be elusive.

If this were my project, I would beg-borrow a 100W transceiver and use it to characterize the amplifier over frequency and input power so that the OP knows what the actual situation is.
Otherwise it is all just conjecture.
73, Don N2VGU

Don,

Its 350W and 1db compression is likely above that.

if he gets 260 hes less than 3db down. If the QRPL amp
is run at 15-18V it will give you more I usually see 11W
at 13.6V and at 16V more like 15W. Also the amp at
20V will produce 25+W. So there is margin there.

That and most devices for that power level might tolerate
20W before becoming fuzes. The BLA350 has a input
sensor and will trip if over 13W.

Myself I'd check the BLA for input attenuator as the apparent
gain is about 14db. Two cases for that, bipolar devices that
would be typical, or Mosfet with attenuator. Looking at the
schematic it has Mosfets and a input attenuator.


--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.

On Sat, Jul 13, 2024 at 05:45 AM, ajparent1/kb1gmx wrote:

So far you have given a bunch of suggestions that does not get him
that 10W and a few that can barely do what he already has. So stop
polluting the topic with wild and inapplicable ideas.

Thank You Allison, I was beginning to feel like Alice in Wonderland !!

The 17dBm output is very attractive, but I'm not sure if it's variable, eg if the "drive control" in the various SDR s/w can control the drive level, or if the drive level is fixed at 17dBm - I've read lots of manuals but so far haven't found anything which states that it is indeed variable, and it always seems to be referred to as the "fixed 17dBm output"

The variable element is required because here in UK for example there is a 100W PEP max license condition for 60m, 32W PEP max license condition for most of 160m, and of course the general principle to not use more power than is required, so it would be much more convenient if I could just adjust the "drive control" in eg Thetis SDR s/w, rather than fiddling about with different attenuators, although the 17dBm level would be just within the safe operating range of an electronically controlled RF attenuator eg


not as convenient as the on-screen "drive" control, but doable.

Once again, thank you

Peter - GM8JCf

On Sat, Jul 13, 2024 at 06:15 AM, John AE5X wrote:

And here is another solution from EU1SW. Costly but offers 14-bit, 6m and 160m and power to run your amp to full output:

I've already got the HL2, the EU1SW is basically an HL2 with a 20W Linear in an enclosure for about USD400 more than what I paid for the HL2 itself. The QRPLabs 10W linear is about USD70 delivered inc taxes etc, so all I need to do is add some relays, an enclosure, 5 connectors, and of course build the QRPLabs kit, which all in all should come in at less than USD150 (assuming that I buy all new parts)

Thanks for the suggestions

Peter - GM8JCF

On Fri, Jul 12, 2024 at 11:02 PM, Steve G4EDG wrote:

I reduced the attenuation and was able to drive the amp to the full 100w with 5w.

Hi Steve

That would mean voiding the warranty, and I'd rather not risk damaging GBP 1,000+ kit if I can do a solid solution with QRPLabs ultra-stable 10W Linear Amp

BTW, do U know where I can get my hands on a BLA-350 plus schematic so that I can add it to the documentation of my BLA-350 plus ?


Thank You

Peter - GM8JCF

On Sat, Jul 13, 2024 at 11:36 AM, G8JCF wrote:

The 17dBm output is very attractive, but I'm not sure if it's variable, eg if the "drive control" in the various SDR s/w can control the drive level, or if the drive level is fixed at 17dBm

I've taken a look at the HL2 schematics, RFFrontend.sch and PA.sch - and the drive to the 17dBm connector, "RF1", and the drive into the 5W PA come from the same pins on the FPGA, so it looks like the RF1 RF level should be variable. Looks like I'll just have to hookup the 50ohm dummy load and 'scope the signal at RF1 and hopefully find out that it's fully variable, now that would be a neat solution.

73

Peter - GM8JCF