New answers tagged

5

Nobody mentions distortion (IM2 and IM3) of PIN diodes and varicap diodes. Tuning (center frequency) limitation range, required band switching and further requirements. Best solution is to start with a good system that can handle the dynamics without filtering. As W8II Phil Frost proposes. ** Mentioned Q-factors (Brian K1LI) of 1000 are not feasible in a ...


13

What limits the use of "solid state variable capacitors" like these for dynamically filtering (low power/received) RF signals? The main issue is bandwidth. Although there are some varicaps that claim a 10:1 variation (or more) in capacitance, not all of this is useable. One end of the range may be low Q, or have a very steep curve. Once you have a ...


4

Another difference between using a varicap for oscillators versus for input filters is feedback. You can feed the output of a variable oscillator into a phase comparator or frequency counter to determine if the component values are correct, and run a feedback loop correction algorithm or circuit to maintain lock. This can be done while the oscillator is ...


1

Consider increasing the dynamic range of the ADC to obtain many of the same performance benefits. This can be done by either upgrading the ADC, or low-pass filtering the ADC input below the Nyquist frequency and oversampling. Often this is the cheaper and more flexible approach, especially given the limitations of the varicap's Q-factor and capacitance range,...


5

Technically, the utility of a variable capacitor in a receive filter depends on the amount of available capacitance variation and its Q - the quality factor, which is the ratio of the capacitor's reactance at the operating frequency to the series parasitic resistance. (In some applications, parasitic series inductance may also be a factor.) Commercially, ...


3

There's a lot of pieces to this question and it sounds like you've already split some of them off to other sites which is good. It's still a little unclear what you're trying to do with the radio itself: Send the audio buffer from the transmitter to the microcontroller In the United States, the Citizens Band Radio Service refers to just one specific set of ...


1

I know this is old, but my friends recommend Troy Radio. They are an authorized FlexRadio shop and specialize in the 5000. You can reach them at: Link: Troy Radio Phone: 254-239-3893 Email: toby@troyradio.net I am not associated with Troy Radio nor ever used their service, but have heard they are good.


2

The real number of samples from an RTL-SDR is not available via the USB interface. The RTL2832U chip samples at 28.8 Msps, but then mixes and downsamples the internal samples to lower rate IQ samples at from 240k to about 3 Msps, to allow transport over its slower USB 2.0 bus. The front-end R820T tuner can first downconvert VHF and UHF signal to a low HF ...


5

The sawbird H+ looks like a nice LNA, do you have the H+ H1 version? The plan version seems to be for 1542 MHz, "center frequency of the module is 1.542GHz with approximately 80MHz of bandwidth (-6dB rolloff). As such, it should be used for reception of frequencies between 1.50GHz-1.58GHz" but the H+ H1 has "65MHz bandpass region, centered ...


Top 50 recent answers are included