QRP VSWR meter that actually works.

I've been searching for a simple and cheap VSWR meter circuit that doesn't use a resistive bridge. The resistive type works well but I've found them a nuisance, as they have to be switched out of circuit when not in use as they attenuate both RX and TX signals.

Just by chance I was doing a Google image search on VSWR circuits when I came across the following from PY2OHH. This design is not easy to find on the web so I thought I would share it with you here.  In most cases I only build the reveres power side of the circuit as this is the parameter I'm normally interested in. I can assure you it works very well indeed, even with a 1mA FSD meter.  However, It does tend only runs out of puff on Top Band where it requires the full 5W to get a meter indication, all the other bands up to ten meters works fine down to 1W.

I plumped for the coiled strip-line version and used a germanium point contact diode, similar to a OA81 device to get the best sensitivity. The design is simplicity itself with no complicated coupling transformers, plus its really easy to align.

The link below takes you to an English version of the design. Miguel is experiencing some issues with his web material so I've copied his design to my Google drive.

PY20HH Design on my Google Drive

Picture from PY2OHH project notes.

30MHz and Above.

Why is there a demise in analogue amateur activity on the VHF and UHF bands, digital modes such as WSPR, FT8, Fusion and DMR are not completely to blame. The release of  digital modes, to Foundation class licenses has, in my mind, caused the problem. If a 24 month period of analogue operation on bands above 30 MHz was included, with QSL proof, became a stepping stone to the next license class it would help. Exposure to the 6m, 4m and 2m band SSB and FM would have made these operators aware of the DX possibilities of these bands, and given them a life long appreciation VHF and above. As it did me as a Class B operator under the old license scheme. I often still sit on hilltops listening for summer tropo signals to appear on hot days and for Sporadic-E openings just before a good Autumn thunderstorm. They have missed all these mystical and magical phenomenon which are a delight to me even after all these years.

Eazy Hi-Z Phones

I was looking at throwing out some scrap office telephones at work but we are not able to dump electronic waste in to our refuse. So I stripped them down to recover the plastics and was left with a pile of electronics. All good stuff , Jolly Useful Necessary Kit (JUNK) - switches, electret microphone inserts, medium impedance earpieces and other goodies like piezo sounders. Seeing the sounders took me back to an article I saw a couple of years ago where an enterprising SWL had fashioned a couple of these sounders into a pair of high impedance headphones.

Now from time to time I like to build a crystal sets just to remind myself why I got interested in radio, trouble is the only devices I have for listening on is one of those uncomfortable crystal earpieces, salvaged from an old hearing aid. So I decided to build a pair of high impedance phones using a cheap pair of ear-defenders and two of the piezo sounders.

The sounders have a very high impedance, too high for normal use, so I wired a 43k Ohm resistor in parallel with each sounder and then placed a sounder each defender ear-cup. I wired them with the cable salvaged from one of the phones in the same configuration as a stereo headset, terminated in a miniature stereo jack plug. This enables the inserts to be wired in series or parallel, in parallel the impedance of 21k Ohms is just about right for crystal set use.

Any sounder can be used, from the type you may find in musical greetings cards to the old trim-phones - bigger the sounder the better the low frequency response.

I'm very pleased with the result, my new headphones are comfortable and have a nice frequency response for communication use, together with a couple of useful resonances for peaking Morse signals - particularly good when used in conjunction with one of my simple valve regen receivers.

Selection of salvaged piezo sounders

Piezo sounders installed in cup including 

original sound deadening foam behind each insert

Finished phones including salvaged curly wire

 

 

Link to original article

https://drive.google.com/file/d/1hubS5vzhiqMuaMFrqDx2c5GLJDHal8lT/view?usp=share_link