HF amplifier purchase

How much current do you need? Can you drive both ends opposite phases?

Some of the THS-series opamps might do it. Maybe use an eval board.

onsdag den 4. marts 2020 kl. 00.42.04 UTC+1 skrev Klaus Kragelund:

think this'll work?

That is usually only the rated load impedance, it's not an internal resistance. Even though a professor (!) at my university was teaching that. A modern transistorized ham radio amplifier has a very low output impedance, a few ohms, but it would (hopefully) go into overload protection if you load it with less than 50ohms at full power.

Starting at 10kHz would be a challenge, you may have to buy or rent a real EMI susceptibility test amp for that. 40Vpp ain't much though unless this has to drive a near-short at lower frequencies. Ham radio amps start at around 1.5MHz and then go to 30MHz. How much lower they can go depends on the construction.

Last time I needed something like that I used an 811A. ;)

Cheers

Phil Hobbs

Have you looked at ENI amplifiers, I think most of them are class A. Probably expensive, here's one, 100watts, 10kHz to 12MHz. 50 ohm output. "The 2100L will work into any load impedance. Into a short circuit or infinite load at some phase angles it may protect itself at power greater than 80% rated power output. Any power reflected due to output load mismatch is absorbed in the amplifier. Therefore, although the output impedance is 50 ohms (maximum VSWR: 2:1), the amplifier will work into any load impedance." "Continuous operation into any load or source impedance"

Mikek

Sorry, they really love these, $9,400!>

To drive 14Vrms into 50 ohms requires 4 W power or 0.3 Arms current.

A small HF amplifier could easily deliver that, but the problem is the required large frequency range 1:2000, so the question is how well the internal transmission line transformers will handle this frequency range. At least the internal transmission line transformer ferrite material may have to be changed.

Some 1:4 or 1:9 external transmission transformers could use to feed also loads of 5.5. 12.5, 200 or 450 ohms.

I would like to have an instrument, so I do not need to spend time on setup etc.

But, I had the same trail of thought, so I ordered this one as a backup solution:

Cheers

Klaus

Yes, this could work for sure :-)

I use the HP 33120A, which has more or less the same specs, 20V into 50ohms, but that limits the power drive, and when driving square wave signals it gets distorted

Cheers

Klaus

That is a nice selection of power HF amps :-)

I would like something with 0 ohms output, but if I am sure I will not short it, I could just open it and short the 50 ohms resistor

Cheers

Klaus

The problem lies with the low end of the frequency range, effectively preventing the use of wideband transformers. Uncontrolled load impedance is something a RF amplifier is not happy with, it makes it necessary to make a far too large amplifier to cope with the surprising loads.

Am 04.03.20 um 00:42 schrieb Klaus Kragelund:

Sounds like a job for a HP3325B fun generator with high voltage option.

Everybody should have one.

regards, Gerhard

Option 002 is also available on the 3325A version. Both use the A8 - High Voltage Output Assembly - 03325-66508

Beware that many of these have been removed from used generators before they are resold. Two of my 3325A arrived minus that board.

THS6022 is a beast.

There are nice tables in AoE-X, but they don't have those line drivers.

Klaus, the THS4031 has only 100 V/us slew rate. Is that going to work?

George H.

Never use THS3062.

The ADA4870 from Lasse looks like a beast! (Did ya see the size of that thermal pad?)

Oh... I list of opamaps not to use and why would be good.

The opa124 has a voltage noise hump ~20 kHz or so... it's been too long.

George H.

Digikey has problems. It finds something else with that name.