[Premium-Rx] Odd behavior by NRD-515

[Cecil Acuff]

Greetings,

Two things to know about this receiver... It has a built I  attenuator for
the BC band that is switched in below 1600khz...

Also when you switch I to the range of the BC band you have a preselected
to tune to peak up the sensitivity.  I forget which knob it's on but it's
marked on  the front panel. If you or your buyer didn't know of that a
greatly reduced level of sensitivity will be experienced. It's also
possible the preselected has a problem and is not peaking properly
resulting I  abnormally low sensitivity.

The preselected only comes into play on the BC band so if you never used it
there you might not have k own about it.

Check that and see if it doesn't help the problem a bit....

Cecil
On Jul 16, 2015 5:14 PM, "Howard Ritter" <hlritter at bex.net> wrote:

> Sorry for the semi-off topic post (somewhere between a Premium RX and a
> boat anchor!), but where else can you get this level of expertise?
>
> I have just had the embarrassing and expensive experience of having an
> eBay seller return the Japan Radio Co NRD-515 receiver he’d bought from me,
> after finding severely reduced sensitivity between 600 and 1600 kHz. I’d
> never used it for BCB listening, so this problem had escaped me.
>
> Briefly, this is a synthesized solid-state GC receiver that tunes a lot
> like the Collins 51-S1, with one knob to select one of 30 1-MHz ranges and
> another knob to tune through the 1-MHz range that’s selected. It’s
> possible, with continuous turning of the tuning knob, to move through the
> ends of any 1-MHz range and into the next. Freq is digitally displayed to
> 0.1 kHz. I simplistically envision the process as that of synthesizing a
> base frequency as specified by the MHz knob and mixing that with a variable
> freq determined by the tuning knob. That’s why I couldn’t picture why a
> decrease in sensitivity would affect just part of just a single 1-MHz band.
> I was skeptical until I got the receiver back and put it on the air.
>
> Sure enough, I found just what he did. In tuning through the single step
> from 599.9 kHz to 600.0 kHz, the background hiss goes from normal to
> virtually absent, a very striking change. Very few stations are received,
> weakly, up to around 1100, above which there is still abnormally little
> atmospheric hiss but a few (strong?) stations are heard. Continuing to tune
> upward, background noise reappears but remains low up through 1599.9 kHz,
> after which it abruptly returns to normal at 1600.0. It’s probably
> significant that this change in frequency is accompanied by the sound of
> what I take to be a relay clicking inside the radio, although there is no
> such sound at 600, or anywhere else in continuously tuning except for
> 4999.9–5000.0 (although when I switch ranges with the MHz knob, the relay
> clicks at 2, 3, and 4 MHz). I have tuned the entire spectrum with both the
> dial and the UP—DOWN switch and have found no other place where the
> sensitivity drops out like it does from 600 to 1599.9. The decrease in, and
> return of, hiss occur whether I tune into the 0–1 MHz and 1–2 MHz bands
> with the MHz range knob or by twirling the tuning dial, and whether I
> approach from above or below.
>
> The band of decreased sensitivity corresponds so closely to the MW
> broadcast band that I wonder whether this is a coincidence. It would make
> sense if the receiver were to automatically switch to a different antenna
> input when it’s tuned to the BCB, and that could explain the sound of the
> relay—except that there’s no separate antenna input for a BCB or ferrite
> antenna. It may be significant that, outside the affected frequency range,
> the background hiss drops markedly when the antenna lead is disconnected—in
> fact, to the same level as the background hiss within the affected range.
> And, within the affected range, the hiss does NOT drop when the antenna is
> taken off. This suggests to me that the RF from the antenna is not getting
> amplified within that range. Still, why or how a problem could affect just
> part of one tuning band and the adjacent part of another band, spanning
> exactly 1000.0 kHz, remains a mystery.
>
> Any ideas?
>
> Thanks,
> —howard n7exn
>
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