AD8307 power meter

Yes, that looks promising.

VBR from Ivan OK1SIP

Ivan wrote:Hi Andrew,
it surely makes sense as a RF wattmeter / field strength meter / ammeter. The main issue with these devices is to make the directional coupling wideband enough, from 1500 KHz to 30 MHz at best. CBers can do with 28 - 29 MHz.  
 
I doubt whether several decades of SWR is needed. IMHO the SWR evaluates this way:
1,0 = ham's heaven
3,0 = I can somehow live with it
10 and more = CRAP!
A better idea would be to make the SWR meter to show the proper value independently from the forward power, i.e. without the need of setting full scale.

VBR from Ivan

In effect, I wonder if the probe will fit inside that box... as for the "setting full scale", no need for that, I was thinking at the circuit shown here

http://electronics-diy.com/electronic_schematic.php?id=952

that one just need an initial calibration, no further adjustment and will work just fine up to around 50MHz; the idea is to use the cal knob on that cheap unit as an attenuator for the FSM/Ammeter when the unit is used for that purpose, the two switches on the front panel would then be used to change the power scale (to be able to measure low or high power) and to select between the FWD/REF metering and the FSM, by the way the unit would also need a power source, and that would mean adding a power socket to the back, but that shouldn't be an issue, and the result would be a pretty accurate instrument, just look at the graphs and measurements at the bottom of this page (that's another AD8307 unit)

https://www.qsl.net/df7tv/pm8307.html

the error is around +/-0.2 dBm on the WHOLE range, not just at full scale, not bad I think

Hi Andrew,
it surely makes sense as a RF wattmeter / field strength meter / ammeter. The main issue with these devices is to make the directional coupling wideband enough, from 1500 KHz to 30 MHz at best. CBers can do with 28 - 29 MHz.  
 
I doubt whether several decades of SWR is needed. IMHO the SWR evaluates this way:
1,0 = ham's heaven
3,0 = I can somehow live with it
10 and more = CRAP!
A better idea would be to make the SWR meter to show the proper value independently from the forward power, i.e. without the need of setting full scale.

VBR from Ivan

I had a (maybe crazy) idea, that is, pick one of those "CBers" cheap SWR/Watt meters, I mean, something like this one

https://www.amazon.com/Mcbazel-Surecom-Strength-Connector-Operation/dp/B08543KYRK



which can also be found at lower prices, open the box (I know what I'll find inside ), remove everything INSIDE (will keep the instruments and switches) and build a dual AD8307 meter circuit inside that box, I think it would be pretty cool, also since someone visiting may be stumbled by the thing and then by the precision of the measurements oh and since that thing also implements a field strenght meter (just a diode and little more), the antenna could be removed, the hole used for a mini jack to connect a clamp-on ferrite OR the antenna, that way the unit may also be used as an RF Ammeter or a field strenght meter, but... with a scale in dB 

Also, and since we're at it, here's the original QST article

http://on4khg.be/wordpress/wp-content/uploads/2015/02/Simple-RF-Power-measurement-W7ZOI-W7PUA.pdf

most other projects based on the AD8307 come from the above one

Just some additional notes, first of all, if you look at the AD8307 datasheet

https://www.analog.com/media/en/technical-documentation/data-sheets/AD8307.pdf

it carries a wealth of infos, plus it contains links to some "next generation" ICs which may replace it, namely the AD8310, ADL5513 and AD8309 (the latter seems very promising), then, the IC (the 8307) could also be used to put together some interesting and useful circuit like, for example, a field strenght meter offering a dB measurement and then some  

Now allow me a little OT, if someone here has some lenght (10m or more - the more the better) of RG58, RG59 or RG6 coax and doesn't know what to do with it, try the following; solder a coax connector to one end of the coax but reversing the connection, that is, coax braid to the connector center pin and coax center to the connector "ground"; shunt the other end of the coax using some resistor(s) offering a value matching the coax impedance, then setup that "coax antenna" in a suitable layout, be it sloping, vertical, horizontal, inverted V or whatever, connect to it the regular coax going to the station and give it a try; the antenna will serve you pretty well from LW up to at least 50MHz and it could be used to transmit too, although in such a case the max power will be dictated by the resistor (willing to go for 100W, a 70W dissipation will be a prudential choice), sure it won't be a beam or a super antenna, but I tried it on holydays and it worked honestly, plus it can be installed almost everywere w/o too much care and won't need an ATU

sm0vpo wrote:Hi Andrew,
This short posting has occupied me for quite a while.

You know me - I hate ICs, but they are sometimes a "necessary evil". I have rebuilt a commercial VSWR/power meter that was advertised as "HF bands" but in fact was frequency conscious, I used the Stockton sensor and now it is flat across the HF bands, but I had to do a lot of "jiggery-pokery" to get it to read power with the ranges I wanted.

The original meter was 2.5W 25W, 250W and 2500W (but I would not trust it above about 100W). In effect I used the box, meter and switches and got it flat, with ranges 250mW, 2.5W, 25W and 250W.

If I had seen this design then I would probably have used something like this design to do the same job. I would have saved a lot of time trying to balance the sensitivity with the measurement loading and still get good results at 250 Watts.
Mine looks a bit "Heath Robinson" and not exactly a show-piece. It is also limited to about 100MHz.

The information on the kits is also interesting. Thank you for sharing the links. I really appreciate this.

FYI, I am now quite occupied with a young lady. Just planning for a cruise in the Mediterranean. I have been very busy with the server upgrades and tidying up the homepages. Updated about 120 HTML documents that had some weirde code in them (generated by Teleport when HHH recovered after a HD failure).

Ok Andrew, thank you for sharing the info. Have a nice day - Harry - sm0vpo

Well Harry, sorry for having been so late, if I knew you were fiddling with such a meter I'd post the infos in advance ! At any rate, that AD8037 circuit is pretty nice, so in case you have some old meter around, you may consider putting together the circuit and bring the meter to new life


Oh and ... do you have any update regarding your antenna ? If everything else fails, you may consider a so-called "random" wire, it will be just a matter of choosing a length here adding a 9:1 transformer like this one (but using an FT240-43 toroid) followed by a good choke like the one shown here and a counterpoise wire and/or a ground stake and you'll have a multiband antenna which, with the help of a matching network (this one is really nice and [url=https://pa0fri.home.xs4all.nl/ATU/FRImatch/dl4cs s.jpg]this version[/url] of the schematic is the way to go imHo), will allow you to cover all bands (ok, depending from the antenna wire length), and by the way, notice that the wire may be laid out as an "inverted L" if there isn't enough space, pick a relatively thin wire and your antenna will be invisible

Hi Andrew,
This short posting has occupied me for quite a while.

You know me - I hate ICs, but they are sometimes a "necessary evil". I have rebuilt a commercial VSWR/power meter that was advertised as "HF bands" but in fact was frequency conscious, I used the Stockton sensor and now it is flat across the HF bands, but I had to do a lot of "jiggery-pokery" to get it to read power with the ranges I wanted.

The original meter was 2.5W 25W, 250W and 2500W (but I would not trust it above about 100W). In effect I used the box, meter and switches and got it flat, with ranges 250mW, 2.5W, 25W and 250W.

If I had seen this design then I would probably have used something like this design to do the same job. I would have saved a lot of time trying to balance the sensitivity with the measurement loading and still get good results at 250 Watts.
Mine looks a bit "Heath Robinson" and not exactly a show-piece. It is also limited to about 100MHz.

The information on the kits is also interesting. Thank you for sharing the links. I really appreciate this.

FYI, I am now quite occupied with a young lady. Just planning for a cruise in the Mediterranean. I have been very busy with the server upgrades and tidying up the homepages. Updated about 120 HTML documents that had some weirde code in them (generated by Teleport when HHH recovered after a HD failure).

Ok Andrew, thank you for sharing the info. Have a nice day - Harry - sm0vpo

just found an interesting circuit based on the AD8307 log amplifier

http://electronics-diy.com/electronic_schematic.php?id=952

it's a quite good fwd/ref meter showing good peecision and allowing to measure power between 10mW and 1KW w/o any switching or calibration, not bad, then the precision of the IC is pretty remarkable, just look here

https://www.qsl.net/df7tv/pm8307.html

to have an idea, not bad imHo