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Bob,
You should try one of these(under $4USD):



3 outputs so you could do LO/VFO and BFO
73,
Gary
WB6OGD

On 8/8/2019 9:40 PM, Bob Macklin wrote:

BTW:

My current interest is to use a DDS to replace the LO/VFO in a NorCal40
and
a NorCal Sierra.

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"


----- Original Message -----
From: "Shirley Dulcey KE1L" <mark@...>
To: <[email protected]>
Sent: Thursday, August 08, 2019 9:28 PM
Subject: Re: [qrp-tech] Spectrum Analyzers?

Software defined receivers are a useful tool. Some of them can see a
wide area of the spectrum at once: about 2 MHz for RTL-type receivers
and nearly 10 MHz for Airspy or SDRplay. The dynamic range of the RTL
receivers is limited and only useful for finding egregious problems,
the higher resolution Airspy and SDRplay are good enough for FCC
compliance testing. You can get software that turns them into a slow
spectrum analyzer by repeatedly retuning the receiver and grabbing
another sample.

SDRs that use a QSD (Softrock, RS-HFIQ, KX2 and KX3, etc) have a much
more limited bandwidth; up to about 150 KHz at a time if you use an
audio card with 192 KHz sampling. They are less useful for broadband
testing, but their excellent low noise performance makes them a great
tool for exploring problems that are near the carrier.

SDRs that use direct sampling (an RF-rate ADC) could in theory do a
spectrum analysis of the entire HF spectrum at once. But it would be a
challenge to build a computer fast enough to do that. And some
incorporate switched analog filters on the input that would make that
less useful.

The spectrum scope features in some of the fancy big name transceivers
can also be useful. The resolution of the display that is built into
the radio is likely to be too low to be useful, but some rigs also let
you connect an external monitor that lets you see more detail about
the signals.

On Thu, Aug 8, 2019 at 11:07 PM Bob Macklin <macklinbob@...>
wrote:

How many people have spectrum analyzers or access to one?

I have read about spurs created by chips like the AD9850. How does a
typical ham checkout one of these devices?

Back in the OLD DAYS (1960's) we used frequency selective voltmeters.
They were very much similar to today's direct conversion receiver.

I have an article from the ARRL on building spectrum analyzer that
works
with an ordinary osciliscope. And I does require a super good scope
because what it has to look at is just low frequency information.

I started building one many years ago.

Bob Macklin
K5MYJ
Seattle, Wa