[NLRS] 2m Pager? noise

[Kirk P]

Ive used this method on HF for SO2R contesting with some success.



I recall the quality o the feedline used has much to do with how well it will perform.


As an update..the FUNCUBE PRO+ with it bandwidth of 196k handles to overload much better than the RTL dongle with its 1mhz bandwidth.


I chose the RTL to use on 2m as it does not perform very well on the HF bands using the upconverter and on good antennas. It tends to get saturated with strong signals even with gain reduced substantially. The FUNCUBE PRO+ performs very well on 6m and HF.


I know several well heeled EME operaters using the RTL dongle with great success on 2m EME but in talking with them, they are not in close proximity to APRS stations like me in the Twin Cities.


So, for the time being, Ill use the FUNCUBE on 2m for MS and EME along with my ARR LNA as it handles the APRS well enough. Ill use the RTL for 6m MS and stick to my ICOM radios for the HF bands until the AIRSPY HF+ becomes available.


And, on a snowy day this winter, Ill take a piece of 7/8 hardline and see about making that coaxial stub.


Kirk

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________________________________
From: nlrs-bounces at mailman.qth.net <nlrs-bounces at mailman.qth.net> on behalf of Doug Reed <n0nas at amsat.org>
Sent: Saturday, October 28, 2017 9:59 PM
To: nlrs
Subject: Re: [NLRS] 2m Pager? noise



If I remember right, if you want a nice tuneable notch, you will use a
cavity on the end of a coax stub near a quarter wavelength long. Pay
attention to the coax velocity factor when cutting the cable. And a
Tee connector in the coax going to the radio, usually a quarter to
half-wave away from the radio. The cavity at the end of the stub gives
a tuneable "open" where the cavity is resonant. At the other end of
the quarter wave it looks like a short at the Tee connector. The
better the coax, the better the "short" and the better the notch.

>From tuning duplexers, I can add that if the stub cable is longer or
shorter than a quarter wave, there will be a "hump" of lower insertion
loss either above or below the cavity frequency. You'd prefer to have
the cavity tuned for APRS to suck out that signal, with the lower loss
"hump" on the EME side of the notch. But you will have to play with
the cable length since I'm not sure if it needs to be longer or
shorter to put the "hump" on the lower side....

I'm going to guess that you probably don't need a hi-IP3 preamp since
the problem is overload of the dongle front end, not intermod. The
preamp gets you a lower noise floor and may add enough gain that you
can afford to lose a few dB in insertion loss from an inline bandpass
cavity. All you can do is play around and see what helps....

73, Doug Reed, N0NAS.






--
Never argue with an idiot, the people watching can't tell you apart.

The problem with suffering fools gladly is that they don’t suffer
nearly as much as you do.
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