1N4148 as RF detector?
Chuck KD9JQ
You might try the HP 1N5712 Microwave Diode.
Chuck KD9JQ
J M Noeding wrote in message <348f3db...@news.online.no>...
>Hi
>Tom Twist(LB8X) and I are planning to build the G3LDI 3-M antenna
>impedance bridge *) and use AD-converter and modify software, we hope
>to find a simple and inexpensive circuit for later publication.
> I need 5 equal diode RF detectors. We will prefer to use some
>commonly available diodes.
> AA118, AA119 or 1N270 germanium diodes will work satisfactorily
> beyond 1000MHz, but they are difficult to find. The only available
> germanium diode in some quantity is 1N34A (and OA85), they have
>proven not particularly good over the frequency range. So I have made
>a test circuit using 1N4148 made on a small piece of single sided pcb
>
> laminate, using short wire ends for good VHF practice.
>
>The result is shown below. I am sort of dissappointed, it seems that
> inspite of having low capacity, the 1N4148 (1N914) have not
> particularly good detected level vs frequency data.
>We will use some software program to calculate between the 5 different
> detected voltages, we may have to use some frequency calibration,
>too.
>Keeping the actual RF voltages higher than 100mV it seems possible to
> use the inexpensive silicon diode as an RF detector.
>1N4148 as RF detector diode.
>---------
>detected level vs frequency for the detector
>shown below:
>
> -----|--1nF---|-1N4148*-|-----|-----|------+out
>RF in | | | | | to Fluke 8020B
>BNC 56R 1N4148 1000pF 10nF 1M
> -----|--------|---------|-----|-----|-----gnd
>
> Detected mV DC @frequency
>Level 5MHz 15MHz 25MHz 35MHz
>30mV 2.1 1.8 - -
>100mV 10.1 9.0 8.0 6.7
>200mV 72 64 57 48.5
>250mV 143 130 118 100mV
>300mV 234 214 195 170
>400mV 438 409 380 340
>500mV 640 605 571 520
>700mV 1157 1110 1055 976
>1V 1964(920) 1900(750)
>1.58V 2960(1380) 2370(1140)
>
>Measured with Wavetek Model 3001A signal generator
>and Siemens 3W518 Pegelsender
>1m RG58/U coax cable
>() refers to a circuit where second 1N4148 is
>replaced by a 100k resistor.
>
>....Jan-Martin
>
>*) Peter Dodd: The Antenna Experimenter's Guide, RSGB, second edition
>1996. ISBN 1 872309 36 4, page 15-28 + appendix page 137-148
>
>----
>Jan-Martin Noeding - LA8AK at online dot no
>N-4623 KristiansandS
>
>Tel.+47-380-87178
J M Noeding
John Woodgate
In article <348f3db...@news.online.no>, J M Noeding
<LA...@ax25.packet> writes
>Hi
>Tom Twist(LB8X) and I are planning to build the G3LDI 3-M antenna
>impedance bridge *) and use AD-converter and modify software, we hope
>to find a simple and inexpensive circuit for later publication.
> I need 5 equal diode RF detectors. We will prefer to use some
>commonly available diodes.
> AA118, AA119 or 1N270 germanium diodes will work satisfactorily
> beyond 1000MHz, but they are difficult to find. The only available
> germanium diode in some quantity is 1N34A (and OA85), they have
>proven not particularly good over the frequency range.
OA90, AAZ15 and AAZ17, also Schottky bridges and general-purpose PIN
diodes from HP. The bridges are said to go to 2 GHz.
--
Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124.
OOO - Own Opinions Only. It is useless to threaten a strong man - he will
ignore you. It is dangerous to threaten a weak man - he will kill you if he can.
Roy Lewallen
>Hi
>Tom Twist(LB8X) and I are planning to build the G3LDI 3-M antenna
>impedance bridge *) and use AD-converter and modify software, we hope
>to find a simple and inexpensive circuit for later publication.
> I need 5 equal diode RF detectors. We will prefer to use some
>commonly available diodes.
> AA118, AA119 or 1N270 germanium diodes will work satisfactorily
> beyond 1000MHz, but they are difficult to find. The only available
> germanium diode in some quantity is 1N34A (and OA85), they have
>a test circuit using 1N4148 made on a small piece of single sided pcb
>
> laminate, using short wire ends for good VHF practice.
You might take a look at "A Simple and Accurate QRP Directional Wattmeter",
QST, February 1990, p. 19, and "The Tandem Match -- An Accurate Directional
Wattmeter", QST, January 1987, p. 18. They describe a novel method of
detecting low-level RF. The former article uses 1N34A diodes. The prototype
unit functioned well up to 450 MHz, but I later found some diodes which
wouldn't operate well above about 2 meters. The second article uses
hot-carrier diodes which are more consistent at higher frequencies. The
technique could be adapted to silicon junction diodes like the 1N4148.
Roy Lewallen, W7EL
ma...@global.california.com
At HP we used to slightly bias the diodes ON so that the "knee" was
closer.
- Robert -
dan
Hi,
You may want to try this with a schottky diode:
------1nF---| -diode-|-----|------+out
RF in | | | to Fluke 8020B
BNC 51R 1000pF 1M
------------|--------|-----|-------gnd
If you don't want to do surface mount,
try the 5082-3080 by hp.
The surface mounts can be had for 50
cents each in small quantity.
Best, Dan.
Peter Bolch
LA...@ax25.packet (J M Noeding) wrote:
> I need 5 equal diode RF detectors. We will prefer to use some
>commonly available diodes.
Hi Jan-Martin,
I have experimented with a broadband RF power meter and found that
schottky diodes are sensitive and work well beyond 1 GHz. E.g. the
types BAT 64-07, BAT 62-03 W, BAT 63 and BAT 17. If the levels to be
detected aren't too low, the HP 2800 Series might be choice.
All the diodes mentioned are available(also in small quantities) from
RS Components (http://www.rs-components.com).
Peter
Dennis Erwin Thurlow
mud wrote:
> The typical 4148 has about 4ns of reverse recovery time.
So what's the EE term for this characteristic?
> That's an appreciable fraction of a cycle at VHF, and will lead to
> quite low rectification efficiency.
I'm going to assume the frequency-to-effeciency curve is NOT linear.
Is there an EE symbol for rectification efficiency?
> The typical schottky ...will be pretty flat up to a Ghz or a little more
Can I assume you are talking about the above mentioned curve, and that
by "flat" you mean linear?
> ...sorting them for Vf.
> you can easily find 5 that match within a single millivolt.
Vf==the forward voltage at which current starts flowing? Something else?
I thought this value was _normally_ just a few millivolts, even for cheapos.
> mud mud mud...mudding...mudder...
Well, ya'. But I'm hoping _that_ can be rectified. :-)
--
geo...@trader.com
Elder - Westminster Presbyterian
TRA #2693
N9VEM
J M Noeding
Hi agn Peter!
Yes, I will look for data and prices for the diodes you mention, and
the 1N5711 and 1N6263. We need diodes for another project, too.
My friend Wilhelm Schürings DK4TJ described a circuit using a/d
converter with minimum detectable level of -30dBm. We are planning to
build something better. My plan is to make a voltmeter with lowest
range of 10mV and max range of 10V RMS, so it would be best if we
could buy only one type of diodes, they must stand at least 30V peak.
So perhaps we may have it demonstrated sometime at Weinheim VHF
meeting....... This instrument should be a modern version of the LA7MI
type I described in DUBUS Magazine in 1986 years ago (using
diode/resistor combinations as gain equalizers)
1) It is important to build 5 equal detectors, so we will not have to
calibrate output voltages for each detector and make special
measurements to calibrate them.
2) Frequency charachteristique should be as good as possible, I don't
want a gain vs frequency correction factor.
I did not have success with the RS homepage, but I have updated
catalog at work, I have also CD for RS and several other
manufacturers, the only problem is that we are not supposed to have
cd drives at work, somebody is afraid that we may install too private
large programs on the PC's !
Another writer mentioned transistor rectifiers with JFET buffers.
I don't rely on JFETs, in my experience gain will vary with
individual buffers, again making it difficult to calibrate each
detector reading against the other. Too often the voltage gain is only
0.6-0.8 for a source follower. Perhaps I am wrong, but I have just
seen too many incorrect applications of JFETs, they tend to be popular
- particularly when one have not studied any performance data.......
I do not wish to go into details of G3LDO's book explaining how the
measurements can be explained, it is based on an algorithm by Tim
Lloyd G3TML. It is a valuable book for the European antenna
experimenter who still believe "homebrewing" has something to do with
experiments, not information about where to buy.....
dan
J M Noeding wrote:
>
> On Sun, 14 Dec 1997 12:16:04 GMT, nc-bo...@netcologne.de (Peter
> Bolch) wrote:
>
> >LA...@ax25.packet (J M Noeding) wrote:
> >
> >
> >> I need 5 equal diode RF detectors. We will prefer to use some
> >>commonly available diodes.
> >
Hi,
You would also like to get Hewlett Packard's Application
Note 64-1A. I found it very informative. They don't
have it in PDF format yet but will mail it.
Best, Dan.