1
\$\begingroup\$

Goal:
Estimate the received signal level in dBm (where 0 dBm corresponds to 0.224 volts) on a spectrum analyzer for a given TV transmitter.

Scenario:
I have many details on the transmitter, including height, frequency, ERP, coordinates, etc. derived from the FCC's LMS database. The Spectrum analyzer is using a "whip" antenna with effectively no gain, and no input amplifier gain. The transmitter has these properties of note.

  • Tx to Rx distance: 13.65km
  • Tx height: 520m
  • Tx frequency: 605 MHz
  • Tx ERP: 650 kW

What I've tried:

  1. Using the FCC's TVStudy command line program, I'm able to obtain the Field Strength accounting for terrain between points using 3 different propagation model options. The results are in dBu for a reference ERP of 0 dBk. This scenario returns around 84 dBu from this program.
  2. In a few real-world measurements, I've measured around -60 dBm for this scenario.
  3. Using a couple online dBu to dBm calculators, I get -68.5 dBm for this scenario.

Question(s):

  • How does ERP contribute to received signal strength in this case? The FCC program does not have ERP as an input. -68.5 dBm is close, but some other scenarios I've tried are less successful.
  • Am I conflating power and voltage measurements, hence making the -68.6 dBm useless?
  • Should I consider another method other than the FCC's program to obtain an estimate of received signal level?
\$\endgroup\$

1 Answer 1

0
\$\begingroup\$

First of all, do all your calculations to determine the signal strength at the receive antenna in terms of power (W, dBm, etc).

Once you have the power at the receive antenna, you need to figure out much of that power is captured by the antenna. When you do this, need to keep in mind that the transmit and receive antenna may have different polarizations.

You can then convert that "captured power" into a voltage using the impedance of the receive antenna and the relationship P=V^2/R.

\$\endgroup\$
3
  • \$\begingroup\$ Thank you! This makes sense. Would you say the FCC field strength result is a red herring for the problem I'm trying to solve? \$\endgroup\$
    – Matt Dale
    Feb 6, 2022 at 16:04
  • \$\begingroup\$ I really can't offer a opinion on that as I have not used that tool. \$\endgroup\$
    – SteveSh
    Feb 6, 2022 at 17:32
  • \$\begingroup\$ But I have used the FCC's DTV field strength map, fcc.gov/media/engineering/dtvmaps. It gives what I assume is E-field strength at the receive location, like this - RX Strength: 57 dbuV/m. \$\endgroup\$
    – SteveSh
    Feb 6, 2022 at 17:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.