Type NDB-2 and NDB-3 RF Milliwatt Meters


Thumbnail Picture - Click to Enlarge


National RF’s Type NDB-2 and NDB-3 RF Milliwatt Meters are affordable pieces of test equipment for both the RF laboratory and the home experimenter. Both provide a digital reading of RF power in dB reference 1 milliwatt of power into a 50 ohm load (i.e. 0 dBm). The circuitry consists of a low noise logarithmic amplifier that drives a digital A/D converting meter circuit. The lowest power levels that can be read are about –73 dBm (approximately 40 microvolts or .00000003 milliwatts). The maximum power input should not exceed 10 milliwatts (+10 dBm or .010 watts) when inputed without attenuation. An internal attenuator is provided and described in the next section.

All controls are located on the front panel. Power is provided by six AA size batteries, which are housed inside the unit. In addition to measuring RF, the Type NDB-3 provides a separate DC output signal, which is scaled to 10 millivolts per dB. Thus, when the meter is used with a swept signal source, such as would be used when sweeping a filter, a useable scope display with a known, convenient logarithmic scale response is provided. Related to this output is selectable filtering, which is used in conjunction with the sweep speed of the swept generator. Both types have a “Low Battery” level display, alerting you to when battery replacement is necessary for proper calibrated readings. A 20 dB front panel selectable Pi-pad attenuator is provided as well on the input circuitry. When this function is selected, a maximum of 250 milliwatts (1/4 Watt) can be inputed continuously, and ½ Watt for short periods of time.


Specifications Common to Both Types NBD-2 and NDB-3

Useful Frequency Range
Maximum RF Input (0 dB attenuation)
   (Internal 20 dB attenuation selected)
Power Requirements

Approx. 15 KHz to 500 MHz
-73 dBm, nomimal, minimum input level
+/- 2 dB, typical
+10 dBm, nominal, continuous
+24 dBm, nomimal (1/4 Watt), Continuous
6 AA size batteries, internally housed
4 in. Width X 5 in. Height X 3 in. Depth


Specifications Unique to Type NDB-3

Auxiliary Output

Output Filtering
Logarithmic DC output level, scaled to 10
mV per dB
1 KHz and 10 KHz (nominal) single pole low pass filtering, front panel selectable


Type NDB-2
Type NDB-3

Shipping/Handling (either type) $7.00 ( in continental United States, only – Hawaii and Alaska $12.00. Shipping outside of the US will be determined separately and billed via PayPal or other means.)

For all California residents, a sales tax of
7 ¾ % applies to the base price of the hardware.

Overseas Customers: Please note that an additional overseas shipping charge will be applied to your order. National RF will notify you of the exact amount of shipping to your country via e-mail, after your e-order is placed. The customer is responsible for all and any customs or tarrif charges applied to your order.

Home - Products - Order Form - Contact Us