Hi Needless to say *demonstrating* this 0.001 db sort of gain flatness on a repeater out to crazy low frequencies is a bit involved. It *is* a great gig if you happen to be a consultant …
Bob > On Nov 29, 2017, at 6:36 PM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: > > -------- > In message <409346f4-60e1-4cae-8602-84fb1c061...@n1k.org>, Bob kb8tq writes: > >>>> The HP3336 with its outstanding level-control is a much >>>> overlooked bargain for this kind of stuff. >>> >>> I looked for the manual, and it seems to have ROM feeding values to a DAC. >>> Is that not DDS? > > That is for the level control, not for generating the signal. > > The level control has a custom HP-chip with two matched thermal > converters, so you can compare the power of two signals with it. > > One signal is the RF output, the other comes from a DAC. > > The 3336 is as far as I know one of the the most precise instruments > when it comes to amplitude, and it was built specifically for the > last two generations of the Carrier Frequency Coax telephone network > (L4 and L5) where up to 10.800 4kHz telefone channels were stacked > over each other in a single coax cable. > > Because the top frequency were near 70 MHz, they needed a repeater > for every mile of cable which is up to 4000 repeaters for a call > across the US. > > If every one of those repeaters had a systematic dip of 0.01dB at > the same frequency, That would amount to 40dB attenuation in total, > so the amplitude tolerances were almost insane, in order to keep > the amount of equalizing manageable. > > Google: bstj53-10 site:archive.org > > It's an amazing story... > > The HP3336 and the HP3586 level meter go together to measure these > lines: The 3586 measures the received signal and when it is done > it tells the 3336 to step 4kHz up to the next channel. The crucial > trick is that the 3336 produces the exact same output level for all > 10800 channels. > > See: HPJ May 1980. > > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
