[NLRS] 2m Pager? noise

[Dr. Gerald N. Johnson]

Yes the noise source and spectrum analyzer using the dongle can show the 
tuning of the filter. The preamp he has can provide the noise spectrum, 
not flat over 100 to 200 MHz, but adequate in the band. I have a paper 
about the use of an amplifier as an almost predictable noise source 
compared to diode noise generators built by skilled microwavers.
http://geraldj.networkiowa.com/papers/2012/predictablenoiseA.pdf

A typical noise source will show peaking, and part of the notch, but 
won't be strong enough to show the notch depth more than about 20 dB down.

I use manually tuned signal generators mostly, sometimes slower than a 
sweeper, but very often less confusing. My HP8640B stays in a VHF and 
UHF receiver SSB passband without tricks, and I mix it to 10GHz with a 
brick oscillator and it stays in the SSb receiver band pass too. My 10 G 
range sweeper in manual tuning mode wanders too much to keep up with a 
SSB receiver. I have also used harmonics of the 8640B at 10 GHz but it 
stayed in the SSB receiver only half the time, as it jumped up and down 
a couple kHz at random. And the level at 10 GHa varied something like 9 
dB for each dB of input change to the diode multipler which made 
checking for receiver MDS very difficult. The mixer scheme works very 
much better. I use a 20 dB attenuator after the mixer so the MDS I 
measure is the receiver, not the mixer. Subject of another paper this 
year. I gave it at Aurora and got it printed in CSVHF, and MUD proceedings.
http://geraldj.networkiowa.com/papers/2017/2017SignalSources.pdf

73, Jerry, K0CQ

On 10/29/2017 5:01 PM, Doug Reed wrote:
> If Kirk decides to build a filter, his biggest problem may be in
> getting hands on a spectrum analyzer and tracking generator to tune
> with and measure the results. Or it may be that enough locals have
> such equipment and he can arrange to meet with them.
>
> But if you want to buy or build something, you can go a long way
> toward a cheap DIY method using your old computer and $50 worth
> of parts.
>
> I've said many times that the $10 rtl-sdr dongle is some of the
> cheapest test equipment you can own. But in today's market, be sure
> you buy a model that comes in a metal case and uses a SMA connector
> and has a TCXO. Kirk probably already has as good or better that he is
> using as his EME front end. There are at least three models I can
> think of that sell or $20-$25 on Ebay or Amazon. The Nooelec and
> rtl-sdr.com versions would be among my top choices. Or the Airspy Mini
> if you want higher performance for $100.
>
> In order to get your spectrum display of the filter, we step back to
> techniques of the ancient radio engineers, we use a noise source and
> peak hold on the SDR spectrum display to get the graphical curve of
> the filter. For $23 you can get the assembled and tested noise source
> board from a USA vendor, or $12 from China.
> <https://www.ebay.com/itm/2016-verison-Noise-Source-Simple-Spectrum-External-Generator-Tracking-Source-SMA/172241109978?hash=item281a5ec3da:g:KGQAAOSwMNxXYASb>
> <https://www.ebay.com/itm/2016-verison-Noise-Source-Simple-Spectrum-External-Generator-Tracking-Source-SMA/172241109978?hash=item281a5ec3da:g:KGQAAOSwMNxXYASb>
>
> Here is the rest of the tutorial on how to do it. Note, there is a
> modified version of the SDR software for doing this. The version has a
> "measure and offset" feature so you measure your setup with nothing
> attached and use it as the "zero offset" for future measurements with
> the filter inline. I must have found it mentioned in one of the many
> other articles this one references.
> <https://www.rtl-sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-source/>
>
> Good luck and have fun!
>
> 73, Doug Reed, N0NAS.
>
>