Frequency finder ignores digital RF transmission.

  Wilham 17:38 07 Jan 2006
Locked

My son gave me an ADSL-2 WAG354G modem for Xmas. Other than the green leds flashing I notice no change except for my happy son with his laptop in next room asking I leave my ADSL switched on when I turn off my PC desktop.

Out of curiosity I put my Scout (model 40) frequency finder adjacent the ADSL, -and had no response. Silly me! Realised my oldish Scout RF counter only goes up to 1.4GHz, whereas this new ADSL transmits RF at 2.4GHz.

A cheap upgrade would be to extend my Scout's range with a simple divide-by-two device called a prescaler. But it appears it would not do the trick because I read this from one in a list of models..."Until now there has not been a generally available digital frequency counter. A normal frequency counter cannot handle digital signals, and results in no display. But the DIGI-HUNTER has changed all that." from click here. (Scroll down to the Digi-Hunter.)

I am measuring the RF frequency not the modulation. Why is a normal RF meter blinded by digitally modulated RF, and how does the Digi-Hunter overcome the problem? My son is a licensed ham yet cannot explain.

Can anyone help?

  amonra 18:44 07 Jan 2006

I think the modem carrier is phase modulated (not certain) so you should be able to pick up a single "spike" at 2.4Ghz while there is something being uploaded or downloaded. I am not familiar with your Scout model, but I think you are pushing things a bit at 2.4G

  octal 19:28 07 Jan 2006

Your old Scout probably won't pick it up as amonra says. The problem is the carrier is not steady but being modulated using Phase-shift keying (PSK) or differential phase-shift keying (DPSK). What this means every time you get a Bit, remember on a simple system there are 8 Bits to the Byte plus the start and finish Bit, it modulates the carrier, so the carrier is not steady but shifting slightly nearly all the time on an Internet connection, its never still because there is a lot of background traffic running all the time, even if the computer is just switched on and not used, in your case the Modem is on all the time so the carrier is never steady.

With all that traffic running the Scout hasn't got a steady carrier to lock onto.

I'm not sure fully how that DIGI-HUNTER works, but I suspect its fast enough to read the mark/space of the carrier shift to give you an average of what the frequency is, of course it won't be truly accurate because it depends on the amount of phase shift between the mark and space, but I should think it would be no more than 1KHz.

As a matter of interest if you could listen to the data stream on a receiver it would sound like a load of white noise.


click here

  octal 19:31 07 Jan 2006

By the way, wish your son 73 from G4LNA, me.

  Wilham 21:42 07 Jan 2006

amonra, octal,..thankyou both for thoughtful responses. It could well be that normal counter/readout can't lock onto the 'wobble', but I'm unaware of such with fm, ringers, and so on because of the bandwith, but the answer may be there. The Scout is a counter, but you're both right, and a wobble could throw a phase locked loop in early stages if there is one.

My son thinks it's a rip-off to promote sales, though I know the web page belongs to one of the most respected firms in amateur radio.

As I write this my son is now 30 thousand ft over the Atlantic on his way back to NY where he works. He reads my postings and will appreciate the 73's, but says he's keen to keep out of my forum 'dabblings'.

Thanks again. W

  Wilham 21:50 07 Jan 2006

octal, your comment on lost accuracy is apt, -the Digi-Hunter only has only 7 digit readout, aganst 10 for my Scout.

  Wilham 22:09 07 Jan 2006

octal, I was slow apprecating your PFK info. If the digital rate is 100Mbs and carrier is 2.4GHz, the ratio is a lowly 24x base(10^8). Well accounts for PSK rather than other mod,,... it makes sense.

All I need now is a circuit of the digi-hunter.

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