Signal Analyzers, Diagnostic Software, Meters, Aiming Devices for OTA

[stampeder]

Google this one: "DIGIAIR PRO Off-Air TV Antenna Signal Alignment Meter"

[danbcman]

Ya thats a beauty too it is the real McCoy.

[tczernec]

Wish I could help out there - I work in the electronics industry but the closest equipment I have at my disposal is a signal generator and a spectrum analyzer. Too bad I'm not at my previous employer, where we had antenna rigs, a microwave network analyzer, and other nice goodies Yaamon did you find someone to test these out?

[stampeder]

Me too - I used to be able to waltz into the lab where I worked and check out the RF and anechoic chambers. Anyone here have lab access to gear like we've mentioned?

No matter, some real world tests will be great!

[mlord]

Yeah, it wouldn't be that hard to test things out.

Just need a tuner with a signal-strength readout, a high quality A-B switch, a variable attenuator (to find the "cliff"), and then some smaller antenuators to trim one antenna versus the other.

All of that stuff is in my RF "junk" box.

One also needs some suitable signal sources across the band -- transmitters at high, mid, and low UHF to compare with, plus some high VHF perhaps.

Those can be analog or digital -- makes no difference to the antenna.

Cheers

[tczernec]

Hmm.. we do have a 10m anechoic chamber at work for EMI testing. I should check if I could get in there for some exra-curricular work I'm sure they have an RF sig-gen and spec-A that would be sufficient. Most EMI chambers though are equipped with a stationary receiver setup (w/ movable wideband receiver antenna) and a transmitter platform for the device-under-test. My understanding is that if we tried to transmit out of one of the 4228/4228HD then we should get the same relative gain results as if we used them to receive instead. In that case, all we need to do is hook the 4228/4228HD to a sig-gen and measure the gain at the receiver. That would give us a good relative indication of the gain difference between the two antennae at all the frequencies of interest. Anyone see the flaw in that logic?

[stampeder]

Tom and Mark, this is a really cool topic so I've split it off into its own thread from the CM4228HD specs thread. Here's a suggestion for a somewhat inexpensive DIY OTA Antenna Lab:

• PC on Linux with available PCI slots
• 2 or 3 pcHDTV HD-5500 ATSC Tuner cards
• PC on Windows
• 2 or 3 different-brand ATSC Tuner cards or USB devices
• TSReader software
• Sheet metal and/or wire mesh materials to change a small room, garage, or barn into a Faraday Cage (or close approximation) with a small one containing the PCs
• RF Signal generator for VHF and UHF TV bands, FM Radio band
• Breakout boxes for quick RG6 patching
• A selection of frequency-tuned baluns
• Another PC on Linux or Windows for running 4NEC2 antenna models

The reason for the pcHDTV cards on the Linux box is that Jack Kelliher wrote some neat Linux command line apps for signal analysis from his pcHDTV cards that can dump their results automatically with some scripting. The TSReader software on the Windows box adds a whole different dimension to the analysis. The different brands of ATSC adapters are so that a composite average of performance can be established that doesn't skew the results due to specific drivers or hardware. The additional 4NEC2 PC would for cause-and-effect testing in real time.

Any other suggestions for a DIY OTA Antenna Lab and/or testing tools?

[mlord]

The HDHomeRun units are even easier to use as signal meters, and they give SigStrength for analog, too (even though they're ATSC only).

Eg.

#!/bin/sh
while ( sleep 1 ) ; do
  hdhomerun_config ffffffff get /tuner0/status
done

Cheers

[stampeder]

So a couple of those HD Home Run units if pcHDTV cards aren't used.

Of course a Volt-Ohm Meter or two as well.

An SWR meter would be good.

Would an oscilloscope be of any use - what waves would we want or need to analyze?

Some reading material on Anechoic Chambers: http://www.glendash.com/Dash_of_EMC/...c_Chambers.pdf

[tczernec]

What would be used as the signal source if you're using a tuner to measure signal strength? Do the signal meters measure received power regardless of modulation, etc.? And do modern RF sig-gens encode some basic ATSC streams? (it's been about 5 years since I've touched a generic RF sig-gen).

I was thinking that for a bare-bones setup (besides setting up the Faraday cage - I like that idea btw) you could use a standard single-tone sine wave at the frequency of interest, feed that into a calibrated reference transmitting antenna, and then attach the receiving antenna under test to a spectrum analyzer that would show you the exact power level received. Of course, this would only allow antenna measurements and not actually test out receiver sensitivity on tuners, but I guess it all depends on what the intended test purpose is. Spectrum analyzers tend to be expensive too, so unless you have access to one via your employer it's outside most folks' budgets.

[300ohm]

Do the signal meters measure received power regardless of modulation, etc.?

AFAIK, TV tuner signal strength meters are the manufacturers approximation of some combination of signal power and signal quality (the digital waveform).

Some tuners have both a signal strength meter and a signal quality meter, which while still far from perfect, is better.

I would like to see them make a TV tuner signal quality meter that would show the actual digital waveform on the screen. It couldnt be all that hard or add much to the cost. It will never happen, but I can wish, heh.

[stampeder]

ATSC modulators are available but I think they're expensive.

Originally Posted by tczernec

you could use a standard single-tone sine wave at the frequency of interest, feed that into a calibrated reference transmitting antenna, and then attach the receiving antenna under test to a spectrum analyzer

Exactly - for antenna testing a simple RF signal generator into some sort of simple reference antenna will do because we're just checking the receiving antenna's gain, f/b ratio, SWR, and its pattern.

[tczernec]

For crude measurements we wouldn't even need an anechoic chamber; a large open area would work too, though that doesn't usually coincide with availability of a 120V power supply for your gear Because we didn't have a chamber at my old employer, we frequently took our gear up on the roof to do our testing. For real measurements, we went to a dedicated testing lab, but at $400/hr for use of their chamber (expensive, but then again each 6x6 absorbing tile in their 10 metre chamber costs $50!) it's a little outside the realm of anyone but companies trying to prescreen and/or certify their products.

[mclapp]

Before I got use of a spectrum analyzer with a tracking generator, I used a UHF Rf modulator as a signal generator. They can be found on auction sites for $20 or less and most will tune from ch14-69+. They're by no means calibrated outputs but for doing comparisons they work just fine.

Mine was able to transmit a long enough distance to test far field readings on most UHF antennas, you might be able to use a disto amp to get a little more signal if needed.

For UHF you don't need to transmit too far to get valid measurements.

ATSC modulators are very expensive.

[stampeder]

Thanks mclapp - that's more along the budget I had in mind and now that I've thought a bit more about an antenna test rig I don't see much need for doing ATSC analysis since they're not directly related.