spectrum or no

radium98 · Post by **radium98** » Sun Oct 02, 2022 8:40 am

What is the possibility or an easy way to find harmonics or sprogs . Without using a spectrum analyser .

yellowbeard · Post by **yellowbeard** » Sun Oct 02, 2022 6:11 pm

Seen this?
https://www.ebay.com/itm/194193379436?h ... BMkpjVmvNg

radium98 · Post by **radium98** » Sun Oct 02, 2022 9:32 pm

Thank you yellowbeard I knew that .and I own a hameg 500 SA . But someone who I forget who did mention a way to find that without SA .But sadly I forget who ?

Albert H · Post by **Albert H** » Sun Oct 02, 2022 11:46 pm

The way we used to do it (way back in the mists of time) was with an Absorption Wavemeter. It's basically a high Q tuned circuit, feeding a germanium diode rectifier, then driving a small meter. My old Wavemeter had a range of plug-in coils, so would cover Medium Wave, Shortwave and VHF up to about 300 MHz with (as I remember) about 14 coils. It had a simple battery-powered amplifier stage to improve the sensitivity of the meter, and there was a sensitivity control to allow you to test a wide range of signal levels.

The RSGB "Radio Amateur's Handbook" used to include a pretty good design for a Wavemeter, and I'm sure that Practical Wireless published designs back in the 60s and 70s.

sinus trouble · Post by **sinus trouble** » Mon Oct 03, 2022 12:44 am

Albert H wrote: ↑Sun Oct 02, 2022 11:46 pm The way we used to do it (way back in the mists of time) was with an Absorption Wavemeter. It's basically a high Q tuned circuit, feeding a germanium diode rectifier, then driving a small meter. My old Wavemeter had a range of plug-in coils, so would cover Medium Wave, Shortwave and VHF up to about 300 MHz with (as I remember) about 14 coils. It had a simple battery-powered amplifier stage to improve the sensitivity of the meter, and there was a sensitivity control to allow you to test a wide range of signal levels.

The RSGB "Radio Amateur's Handbook" used to include a pretty good design for a Wavemeter, and I'm sure that Practical Wireless published designs back in the 60s and 70s.

From what i gather? Albert is referring to a basic signal receiver circuit?

In theory? You could also do it with a decent scanner? Logging all data points and extrapolating them into something useful!

Worst case? If your transmitter is dreadful? The scanner will lock onto several points surrounding the "Carrier"

Harmonics tend to follow a pattern! Usually multiples of your carrier frequency!

radium98 · Post by **radium98** » Mon Oct 03, 2022 6:59 am

Thank you guys.

Albert H · Post by **Albert H** » Mon Oct 03, 2022 7:58 pm

No. Unfortunately, most "scanners" are prone to finding all sorts of spurious responses - usually developed within the receiver itself! It's usually impossible to discern real spurs and harmonics from the internally generated crud!

The basic Wavemeter is a tuned circuit with a high Q coil and a good quality variable capacitor across it. One end of the tuned circuit is connected to the metal box that houses the instrument, and the other feeds a germanium diode (silicon diodes are too insensitive). The diode feeds a high sensitivity meter movement. I used to use the "Record Level" meters that you could get from "Henry's" in Edgware Road - these were 100 µA full scale.

A slightly over-complicated circuit is at https://www.qsl.net/g3oou/absorptionwavemeter.html - you won't need to build the HF part (unless you're planning Medium Wave or Short Wave equipment construction). Mine had a TL072 dual op-amp to drive the meter, and it ran from a PP3 9V battery. I had plug-in coils wound around the plastic cases of 2-pin "Loudspeaker" DIN plugs. It was selective (and sensitive) enough to peak up the tuning of transistor frequency multiplier stages, and clearly showed the 4.5MHz spurs either side of the carrier from a poorly built 40 Watt transistor power amplifier that had low frequency instability / oscillation!

I built a few of them over the years, and the best one was built into a small "Eddystone" diecast aluminium box. I also built my first frequency counter into a similar diecast (using a calculator 7-segment LED display), an early ECL prescaler IC, and an ICM7216 frequency counter chip. It was a real battery-eater, so I got a rechargeable pack for it, and found that I had to re-charge it after about ½-hour of use!

sinus trouble · Post by **sinus trouble** » Mon Oct 03, 2022 11:23 pm

Albert H wrote: ↑Mon Oct 03, 2022 7:58 pm No. Unfortunately, most "scanners" are prone to finding all sorts of spurious responses - usually developed within the receiver itself! It's usually impossible to discern real spurs and harmonics from the internally generated crud!

Sorry Radium! Albert has got a point! Afterall, it was just a theory!

I sounds to me like it will be a tedious task whichever way approach it?

radium98 · Post by **radium98** » Tue Oct 04, 2022 7:11 am

Thank you no problem at all we learn.it is just a bit of fun.Honestly 3 years ago I started to build such a dip meter before vna .but I stopped due to some metal construction . Even I built the vhf b3 coil .I will put the source and what I did here .the tuning cap stopped me .

reverend · Post by **reverend** » Tue Oct 04, 2022 10:30 am

You can usually tell if something is 'sprogging' because when you slowly rotate any variable (such as a capacitor in the PA) the output power jumps rather than varying linearly.

Harmonics are more difficult to detect, and any receiver nearby a transmitter is likely to be overloaded and can produce harmonics in the front-end. Also, if you run a transmitter into a dummy load, and the transmitter is not well shielded, you can sometimes receive stronger harmonics than the fundamental (i.e. as radiated by the output filter). The best test with a receiver is to fire up the TX into an antenna and then go a reasonable distance away (a coupld of hundred metres) and see whether you can receive the harmonics - they should be pretty weak, if receiveable at all. The antenna will have some impact on reducing the harmonic output but that's fair, becuase it's the radiated harmonics that matter.

Albert H · Post by **Albert H** » Wed Oct 05, 2022 1:11 am

Way back, when I was engineering UHF TV transmitter installations, we used a "Tuned Cavity Wavemeter" - a huge contraption built in a large steel box about the size of a 6-drawer filing cabinet! It had castors, and was so heavy that it took two of us to wheel it about! Inside the box, there was a tubular cavity with a plunger affair that went up and down inside the tube and (effectively) varied its overall volume, thereby tuning it, and this was adjusted by a very long, threaded "bolt", that mechanically connected to a big control knob with a "turns counter" on the top of the box. There was also an enormous air-spaced fixed capacitor that would resonate the cavity. There was a "sniff" coil in the bottom of the cavity (below the lowest point that the plunger could reach), and this was fed to a rectifier (water cooled!) and a meter movement on the front of the case. It had various RF connectors provided on the outside of the box, and it was labelled with the maximum power it could handle and the range of frequencies it could tune. Despite being built like a tank, and so damn heavy, it could only handle about a hundred watts (50 dBm)! The Manual had pages and pages of "look-up table" that converted the Turns Counter readings into frequencies!

We used to feed it from a "sense" coil assembly in the PA output cavity, and it would show every spur and harmonic from 460 MHz to nearly 2 GHz. The tuning was sufficiently precise to be able to discriminate between the vision carrier and the sound sub-carrier just 6.7 MHz away!

We were all glad when the 22 GHz-capable HP 141T series Spectrum Analysers arrived!

radium98 · Post by **radium98** » Wed Oct 05, 2022 7:27 am

thanks all

EFIALTISFM · Post by **EFIALTISFM** » Wed Oct 05, 2022 1:47 pm

Haven't seen anyone comment on yellowbeard's post so...

Would these TinySA portable "budget" units (or something like a LATNEX WSUB1G+) do a decent job on freq scan and harmonics?
... not comparing them to the big $ analyzers!
^

yellowbeard's wrote: ↑Sun Oct 02, 2022 6:11 pm Seen this?
https://www.ebay.com/itm/194193379436?h ... BMkpjVmvNg

Albert H · Post by **Albert H** » Wed Oct 05, 2022 8:54 pm

I've got one of those here. It's a bit of a toy, but it does show harmonics. It will also show up some spurs, but is very prone to overload, and appears to have protection diodes on the input that cause the display to fill with random responses if they go into conduction!

Here's mine:

Little Analyser.jpg

sinus trouble · Post by **sinus trouble** » Thu Oct 06, 2022 12:13 am

Nice Albert!

The thing i do like about those "Tiny SA" is the direct connection which avoids outside influences!

However, that means that some sort of attenuator or coupler is required!

But i guess you get what you pay for!

Albert H · Post by **Albert H** » Thu Oct 06, 2022 12:28 am

It's sensitive enough that you can connect a short aerial, and receive "off air". It's quite useful as a pocket instrument on site, especially when looking for "conducted RF" on cables. You'd be surprised how far down the mains (or down data network cables) RF signals can get!

sinus trouble · Post by **sinus trouble** » Thu Oct 06, 2022 12:44 am

Interesting Albert! I never thought of that kind of application!

I think another significant aspect to these products is that technology is moving so fast!

Something that was deemed virtually impossible many years ago! Is now reality!

Amongst the usual "Crap" floating around, There is often something useful to be found!

yellowbeard · Post by **yellowbeard** » Thu Oct 06, 2022 4:31 am

All of the advancements like this, the MiniVNA and HackRF One are a part of a revolution brought about by software defined radio. The computer Johnny's are doing man-sized jobs in the field, and I used to curse them out when they started taking over the pages of my favourite electronics magazines. It's a far cry from the days of old with bottles, rollercoasters and variable toast racks.

radium98 · Post by **radium98** » Thu Oct 06, 2022 3:56 pm

that what i have .

radium98 · Post by **radium98** » Thu Oct 06, 2022 3:57 pm

i need a voltage amplifier from few mV to some volt , anyone ?

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