Rectifying RF

Low barrier schottky. SMS7621, BAT15, something like that.

I have a Spice model somewhere, if you're interested.

--

John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Too many details are missing. What kind of meter? What impedance? The 1M

60 was used in millions of TVs as the video detector. Look at the manual fo r theBoonton 92 or 9200 series to see how they work down to Microvolts with two diodes and a chopper circuit. The 92 Series uses a mechanical chopper while the 9200 uses an electronic chopper. I have both. The 9200 is expensi ve, but digital and it can be computer controlled.

How do you plan to calibrate a home made probe?

I would start with whatever I can find in my junk box. 1N4148 or

1N914 probably. If you want more sensitivity, 1N34A or 1N270 germanium in a voltage doubler configuration. Keep it simple or you'll never get around to actually building the RF voltmeter probe.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Am 24.12.19 um 16:22 schrieb Cursitor Doom:

< > < > < >

There are more.

regards, Gerhard

I suggest you check out Barrie Gilbert's amazing RF log-converter ICs. RF-in, DC-out. Accurate over a huge range of amplitudes and frequencies.

--
 Thanks, 
    - Win

Use a fast diode as suggested

About the low level, use ac coupling and add a resistor offset to null the output

Cheers

Klaus

Just about any diode will have a forward voltage drop of at least a couple hundred millivolts.

Perhaps a simple transistor amplifier will raise levels enough so the error will be tolerable. Suppose your amplifier had a collector resistor of 10K, emitter resistor of 1K. Voltage gain would be 10, assuming no emitter bypass and high load impedance.

Fred

BAT46 seems to be a perfered sub for the 1N60.

Cheers

+11

What do you actually want to do ?

Are you interested in a calibrated RF voltage reading of any frequency from 0 to 30 MHz ?

Or are you just interested in getting some relative RF voltage reading so that you can tune e.g. IF transformers ?

For tuning VHF/UHF frequency multiplier stages, I have used simply

1N4148 in shunt configuration and used a 25 uA (2 kohm) current meter as indicator. Of course the current meter loads the RF circuit quite heavily, which is not so much an issue at typically VHF/UHF circuits with low impedance levels However, this might be a problem an on MF/HF due to typically higher resonance impedances, so some higher impedance voltage meter may have to be used with less sensitivity.

DVM update rate is often too slow for RF stage tuning, so use an analog instrument.

The Analog Devices AD834 is a 500mHz four quadrant multiplier chip

The data sheets mentions it's use a a power meter - if you feed the same signal into both inputs the DC content of the output is proportional to the square of the input amplitude.

Futzing around with diodes is for hobbyists.

--
Bill Sloman, Sydney

The best load resistance for a zero-bias detector is infinite. Low-barrier schottkies have dependable reverse leakage to discharge the cap.

--

John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I personally don't want to do anything. The question is from my PoV entirely theoretical. I wasn't seeking tips on how to proceed with some project so much as seeking specific answers to the questions I posed. This curiosity arose out of a visit to a friend who had just replaced the final PA tubes in a vintage ham radio and needed to neutralize them. Since he's partially disabled, I went around to assist him. Straight away, however, I was not happy with his improvised arrangement for a dummy load. The load itself might just have been get-awaywithable for HF (the tx section topped out at 30Mhz) - might. He'd made the load from a couple of dozen resistors but they were through-hole types and he hadn't made any effort to trim the leads down. Furthermore, in place of an RF millivoltmeter, he'd cobbled this home made dummy load together with a 1Nxxxx jellybean diode and cap for rectification and 'filtering' and then used a choc-block connector to hook up a cheap chinese DVM's probes and intended to use the DVM for the measurement. I immediately removed all that unsightly gubbins and we carried out the procedure instead using a comms rx I'd brought with me that had suitable attenuation and a good old-fashioned moving coil meter. And that's all there is to it. I was just curious as to whether *if* we'd proceded with his amateurish gubbins we'd have been able to pull off the measurement satisfactorily. Somehow, however, I doubt it!

--

"When constituencies are small their elected representatives must concern themselves with  
the local interests of their constituents. When political representatives are distant and  
faceless, on the other hand, and represent vast numbers of unknown constituents, they  
represent not their constituents, but special interest groups whose lobbyists are numerous  
and ever present. Typically in Europe a technocrat is an ex-politician or a civil servant.  
He is unelected, virtually impossible to dislodge during his term of employment and has  
been granted extensive executive and even legislative power without popular mandate and  
without being directly answerable to the people whose interests he falsely purports to 
represent."                                        

 - Sir James Goldsmith (Member of the European Parliament) 1933 - 1997

Thanks, Win. This might actually be very useful for another application I may be working on shortly. I have a vector network analyzer that has a not very good AGC - there's actually clearly a fault with it as when I tune from 4Mhz to 1300Mhz the final output amplitude goes up and down all the time by quite an alarming amount. The spec states it shouldn't vary by more than 1dB throughout the entire range, but it's nowhere near that. Anyway, that's really the subject of another tread, so we'll say no more about that at this time....

--

"When constituencies are small their elected representatives must concern themselves with  
the local interests of their constituents. When political representatives are distant and  
faceless, on the other hand, and represent vast numbers of unknown constituents, they  
represent not their constituents, but special interest groups whose lobbyists are numerous  
and ever present. Typically in Europe a technocrat is an ex-politician or a civil servant.  
He is unelected, virtually impossible to dislodge during his term of employment and has  
been granted extensive executive and even legislative power without popular mandate and  
without being directly answerable to the people whose interests he falsely purports to 
represent."                                        

 - Sir James Goldsmith (Member of the European Parliament) 1933 - 1997

There are a lot of common 1Nxxx SIGNAL diodes useful for that. Low level (100mV) signals? Adjust the forward bias.

Well, well. I wonder why no one else mentioned that!

--

"When constituencies are small their elected representatives must concern themselves with the local interests of their constituents. When political representatives are distant and faceless, on the other hand, and represent vast numbers of unknown constituents, they represent not their constituents, but special interest groups whose lobbyists are numerous and ever present. Typically in Europe a technocrat is an ex-politician or a civil servant. He is unelected, virtually impossible to dislodge during his term of employment and has been granted extensive executive and even legislative power without popular mandate and without being directly answerable to the people whose interests he falsely purports to represent."

- Sir James Goldsmith (Member of the European Parliament) 1933 - 1997

Start by looking at the AD8307. Direct dBm to linear voltage reading.

One clever application of the AD8307 RF log-converter was used to listen to the pilots talk while riding in an aircraft. Aircraft radio is amplitude modulated. A simple tuned circuit at the input and earphone(s) AC coupled at the output. Can't remember if additional audio amp was used. Battery powered. It has no oscillator, so could not interfere with the aircraft equipment.

Dr. Wenzel did that at my request for back when I still had time for Ham Radio and had no instruments except for a frequency counter. Now I have a good RF bench to 20 Ghz.

Steve