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Categories | Filters, Audio: (DSP and others) | JPS NTR-1 Help

Show all reviews of the JPS NTR-1

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KD7RDZI2  Rating: 5/5 Apr 20, 2019 15:22  Send this review to a friend!
Updated review: 25Y treasury  Time owned: more than 12 months
I bought it new in 1994 when I entered in the hobby as an SWL. It was pricey at that time, 159$. But I did not expect such a long 'duration' for this ham 'asset'! So considered the time I have used it, I spent really pine nuts, almost 6$ per year!

Evidently it was built accurately, good components and good design. Well protected in the audio input and in the power supply input.

This was one of the first DSP filter appeared in the ham market, so it may be considered ancestral technology. Ads of that time exaggerated the about the effective noise reduction. But I have to say, the notch filter works spectacularly with multiple tones beyond imagination without distortion. The unit has two bandwidths, 6.6 and 3.4Khz and looking its spectrum with SDR software the filters are very effective. The ADC used has 14bits, so dynamic range should be theoretically 84db, which should be more than adequate being really the last stage be chain after the filters built in the radio.

Then we have noise reduction which in my opinion works well in digital modes and rather well with speech. It does not make miracles but it helps.

The unit being external and well screened does not interfere in any way with the circuitry of the radio.

Operatively it is very easy to use but still it is worth to understand its manual and circuitry. The audio input is an op-amp which is a very high-impedance. At audio level impedance mismatch is not an issue at all. You can either use a high impedance output or a low impedance output such as speaker or headphones outputs of the radio. The op-amp is a unity gain buffer amplifier. I have added a small audio (data) isolating 1:1 transformer between the high impedance output of the rig and the NTR to totally remove any possibility of ground loops. In the case I use the speaker output I have added a 4:4000ohm audio transformer between the speaker output of the rig and the NTR1. I could have used a simple 1:1 transformer, however, the transformer rising the impedance, rises the mV delivered into the NTR, so in practice it rises a lot the volume (the input level should receive between 100mVRMS and 2VRMS). Also I have added some homemade RC high-pass filters to remove basses (between 0 and 350Hz).

Overall I am very satisfied. I can use it with any radios, especially mine that mostly are old, surplus and analog.

I don't own typical modern transceivers to compare. But I have a Softrock Ensemble II SDR. The SDR performance depends on the software used. I have to say the notch of the NTR is unbeatable and the noise reduction in the SDR softwares I have used is not much better than the one in the NTR.

As a bottom line, the latency in the NTR is close to nil. 
Product is in production.
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