Old TV field strength meter any good?

I have a Sadelco 719E Signal Level Meter that I bought when I retired 20 years ago. I have found it very useful for aiming the antenna, finding the best "hot spot" for the antenna, and comparing antennas. It was designed for analog signals so it doesn't give the correct absolute value for digital signals, but it does give reliable comparisons.

For further information please see my post #98 on the Channel Master CM 4228 8-Bay Bowtie UHF Antenna (CM4228)thread:
www.avsforum.com/avs-vb/showthread.php?p=14530126#post14530126

The older meters were called field strength meters and they were calibrated in microvolts (1000 microvolts = 1 mV = 0 dBmV). If you buy an old one, make sure it does UHF & VHF.

For checking she signal strength of digital channels, no. It is an analog meter -- it can't read the digital signals. Assuming that there are analog channels at the same location (or close by) as the digital transmitters, it can be used to orient an antenna.

I also thought my NTSC meter would be useless for digital signals until I actually tried it. My meter has an audio feature: The analog signal (video carrier) has a buzzing sound; the digital signal sounds like white noise (like FM carrier interstation noise with tuners that don't have interstation muting).
Meters that are designed for analog signal measurement use peak reading; digital signal measurement is an average value which accounts for the reading error when using an NTSC meter to read digital signals.

AntAltMike adds a correction factor of 8 dB to the reading on his Leader LF941 analog signal meter (the new LF941D is for digital) when he measures a digital signal:
www.avsforum.com/avs-vb/showthread.php?p=14236123#post14236123

The downside: Since my meter gives the information that I need to deal with digital signals, I have lost, for now, my excuse to buy a new one!

My NTSC meter will give a reading on analog and digital signals. I have been refining my measurement technique this year because I have both analog (at least until Feb 09) and digital signals available in my area and feel confident about my conclusions.

I'm not too concerned about the calibration of my meter because I use it to aim antennas, find the best location for antennas, and compare antennas---which only requires looking for a maximum reading. It is easier to see a peak or a null with a panel meter that has a needle than with a digital panel meter, even if it has a bar graph. The linearity of the meter IS important. I can check it with a steady signal that gives a reading in the upper part of the scale and insert the 20dB attenuator which should lower the reading by 20dB. The older meters that have a top scale in microvolts instead of dBmV often have an attenuator marked x10, which is ten times the voltage---the same as 20dB.

Even if you use a sophisticated piece of equipment like a spectrum analyzer, it scans its analog-type measurement window across the desired frequency range not unlike when you turn the dial on the NTSC SLM to move the measurement window to the desired channel. And, it is often necessary to add a correction factor for the internal characteristics of the analyzer sweep or for external devices like a 75 to 50 ohm minimum loss pad to obtain the absolute dBm value.

I can also compare the strength of local signals using my readings to find out which signals are the weakest and need the most help. Using an adjustable attenuator between the antenna and a digital TV or CECB I can measure how much margin I have before dropout, which is similar to the NM-Noise Margin figure on Andy Lee's excellent TV Fool website. This method is further described in the Kelvin link in my signature. Once I know how much margin I have, I can tell how close I am to dropout just by looking at the meter reading.

An alternate method is to use a splitter to feed the TV or CECB and the meter after the attenuator to see exactly at what level dropout occurs, allowing 3.5 dB loss for the splitter. This gives me a calibration point for dropout on my meter.

An interesting experiment is to use a CECB that has dual signal bars, like the Zinwell ZAT-970A. As you increase the attenuation the signal quality bar will suddenly drop to 0% at dropout indicating that the error correction system (FEC) can no longer keep up. My Channel Master 7270 attenuator has 3 dB as the lowest step, but our north-of-the-border friend Autofils (of Gray-Hoverman fame) has found a source for inexpensive fixed value attenuators which include a 1 dB value:

www.mjsales.net/items.asp?FamilyID=221&this_Cat1ID=265&Cat2ID=93

Autofils has been encouraging the use of the attenuator dropout technique ("cliff-effect" measurement) as an inexpensive way to compare the actual performance of DIY antennas with the predicted computer simulation. The attenuator setting at dropout for the DIY test antenna minus the setting for a reference folded dipole for the same frequency gives the gain of the test antenna in dBd:
http://www.digitalhome.ca/forum/show...&postcount=216
http://www.digitalhome.ca/forum/show...&postcount=253
http://www.digitalhome.ca/forum/show...&postcount=308
http://www.digitalhome.ca/forum/show...&postcount=274
http://www.digitalhome.ca/forum/show...&postcount=283

John:
Thanks for the positive feedback and information about your antenna system.
I'm glad that I was able to help you.

Question:
What is the model number of your meter?

if you dont mind spending some cash, This is the one that I use and it works well. http://cgi.ebay.com/digiair_W0QQitem...3A1|240%3A1318

FS-3, excellent! When I bought my 719E the FS-4, with tighter specs, was available for a little more money.

The position of the channels on the UHF dial is affected by the position of the fine tuning knob, if it has one. On mine, the fine tuning knob has to be at about 5 o'clock for the channel numbers to line up. But, with digital signals the adjustment of fine tuning knob is not as critical as with the analog video carrier because the digital signal almost fills the whole 6 MHz channel. If you notice a notch or dip as you slowly tune through the digital signal, you have a serious multipath problem.

Thanks for telling us about your DigiAir and giving a link for more information.

I haven't used the DigiAir, but I think that EscapeVelocity has. The narrow input level range of 25-100 dBuV might be a problem for some users, if the specs are correct.

I just purchased a used Blonder Tongue FSM-11 through eBay for $65. It sold for $1,287 new. You can tune in both analog and digital carriers. After all even though the signal is transmitting digital information it's still RF. Why shouldn't it work. You just hear noise on the audio, no TV audio or video buzz when you tune a digital carrier.

Congratulations on picking up the FSM-11 for such a good price. I saw it listed and was tempted. It looked like it was in excellent condition. But, I already have too many signal level meters! Also, I'm pretty much a Sadelco fan. It should work and it does work for digital signals for me and many others.

I also saw a very expensive analog signal meter made by Potomac that is used by broadcast engineers. There is a Potomac manual that says it can be used for digital signals if the proper correction factors are added to the measurement.
http://www.pi-usa.com/pdf/dtva.pdf

I'm not too concerned about the correction factors because I use my meter mostly for comparisons---more is better! Or as the British hams say when they are tuning up their transmitters: "Tune for maximum smoke!"

If using a meter designed for analog signals to measure digital signals is good enough for broadcast engineers, it's good enough for me.

But it is not good enough for me. Broadcast engineers don't demand as much from their meters because they are aiming a tuned antenna on a high tower at a single transmitter. People here are faced with the much more daunting task of developing acceptable signal quality from transmitters in different directions. For that, you cannot beat a specrum analyzer that lets you simultaneously evaluate the flatness of all your signals.

AntAltMike:
I have been focusing on signal level on this thread because that is what the OP was asking about, but your point is well taken. That's why I'm now using a Signal Level Meter for signal strength and an Apex DT502 signal quality bar for BER. I'm finding out that even if I have a strong signal, I will not be able to maintain lock if the BER is more than the FEC can handle. I have seen this happen with strong signals that have multipath problems.

Maybe someday I can upgrade to a Signal Level Meter that also does BER.

A spectrum analyzer, which is a very elegant and useful piece of test equipment, is out of the reach of most of the posters on this forum. That is why I have been trying to find less expensive ways for them to solve their reception problems.

Funny thing about BER measurement. It is the errors incurred by the tuner/demodulator/decoder in that meter, which will not always correspond with the bit errors incurred by your TV tuner. I am presently going through hell troubleshooting a master antenna system in a 500 unit building less than a mile away from the transmitting towers in which I heterodyne convert nine locally broadcast VHF down to nine vacant VHF channels, and you can't imagine how much the decoding success varies from one brand decoder box to another, and it isn't a matter of one being better than another. Some boxes tune some qualitatively substandard channels well while others not at all, while another box tunes the ones the others can't tune but fails to tune some of the others, and there is no reliable correlation between the success of a tuner to decode a chanel and the BER shown on my Blonder Tongue BTPDA-4 meter.

Too bad you can't decode once and re-modulate, but I guess the equipment cost for that is well out of reach.

Your problem demonstrates the need for a BER meter standard. I hope that better and less expensive BER meters will become available, considering the importance of signal quality for digital reception.

Fortunately, I don't have that problem. When I use the Apex DT502 as a BER meter it is also my tuner.

Maybe the situation will improve when the new ATSC M/H standard training signals are added to the transmitted signal. http://www.tvtechnology.com/article/61736
http://www.tvtechnology.com/article/16632
http://www.avsforum.com/avs-vb/showthread.php?t=1029236

Or, maybe the US should have adopted something like DVB-T instead of ATSC, with its better abililty to handle strong multipath reflections inspite of its need for greater SNR that could be handled with an increase in ERP for the same coverage area:
http://www.bbc.co.uk/rd/pubs/papers/.../crn-dvbtm.pdf ATSC vs DVB-T, excellent charts on p3

The least expensive measurement tool that I have found for the average poster with reception problems is the DT502. It gives signal quality, signal strength, can be used to aim an antenna with the signal strength bar, the aim can be "tweaked" with the signal quality bar to find the best direction that minimizes multipath reflections, and it will allow reception of digital signals on an analog TV all for only about $10 and a coupon without a long learning curve.

The next step up is what I'm using: A signal level meter, that costs (used) about as much as CECB, for signal level values and a CECB with a signal quality bar for BER.

The next step up would be a tuner card for a PC and the software that gives SNR, BER, & etc. This is a little more costly and requires a longer learning curve.

If anyone knows of a better easy and inexpensive measurement method that we can suggest to all the posters with reception problems that we are going to get after the transition I would like to hear about it.

I've had my worst luck with couple of GE CECBs that one of my customers bought. Even though her signal strengths are all around -20 to -30dBm, and even though her S/N ratios are all well over 20dB, her boxes only lock onto three of the nine channels and they even pixelate on one of them. I'm going to buy one off her and use ot as part of my traveling test gear, as the tuner in my $110 Best Buy,Dynex 13" CRT is so good at procesing qualitatively poor channels that it is not useful for confirming signal quality adequacy.

Sadelco huh? That's Cool! Yes, my BT FSM-11 is in very good condition! The only thing wrong is the plastic lid cover over the knobs is broken, it just lifts off instead of hinging up. However, that's fine with me. The owners manual states that most techs prefer to work with the cover off anyway. I just use it to cover my knobs when I store it. There is now the same model on eBay with the volume knob broken and the asking price for it is $950.

I am getting back into the antenna installation business right away. I feel there will be a need for this with the DTV switch. It is going to be so nice to tune the antennas right on target instead of guessing like I did in the old days.

It looks like you got the better one at a good price.

Keep in mind, with digital, signal quality (BER) is just as important as signal strength, especially with multipath problems.
http://www.wowvision.tv/signal_strength_meters_BER.htm
http://www.wowvision.tv/HDGlossary.htm Glossary
http://www.wowvision.tv Home

The factors that reduce signal quality and cause a higher BER are:

1. Improper signal level: A weak signal will cause a poor signal-to-noise ratio; a signal that is too strong can overload a tuner or preamp. A nearby FM transmitter can also cause overload, which would require an FM trap.
2. Reflections from multipath problems.
3. Impulse noise in the reception area.


Please let us know how the meter works out for you.

Well, guys, my moment of truth has arrived. Here are my measurements of digital and analog signals using both a digital and an analog signal level meter (SLM).

Because my wife and my friends were VERY generous to me at Christmas, I am now able to compare readings from my Sadelco 719E with readings from a DisplayMax 800.



I wanted to do this before the transition while I still had a good selection of digital and analog signals coming from Norfolk. I picked 6 signals, 3 digital and 3 analog. The virtual number indicates digital. The measurements, including the ones for CH13, were made using a CM4221 antenna. I used a splitter to make simultaneous readings on both meters because OTA signals don't stay at the same level.

And as a chart:



The chart gives me the corrections needed to make correct readings of digital signals with my analog signal SLM, but I'm really not too concerned about corrections because I mostly use my SLM for comparative readings to aim antennas, compare antennas, and find the "hot spot" location for an antenna. These comparisons rely on the the linearity of my meter which is easy to check by inserting a 20dB attenuator to see if the reading drops by 20dB.

The corrections are the result of differences in the calibration of the SLMs, the tolerance allowed for each SLM, and the fact that analog signals are measured with a peak value of the video and sound carriers and digital signals are measured with an average value across most of the 6MHz channel. Sadelco says in the manual that two 800 meters can differ by as much as 2dB and still be in spec.

My 719E is reading too high on digital and analog signals because it is off calibration on both. If it were on calibration the red line would be lower all across the chart, its readings of analog signals would be the same as the 800 readings, and its readings of digital signals would be a lot lower. This would make it necessary to add a positive correction to the 719E reading for digital signals, which is what it is supposed to be. It was just a matter of luck that both meters were fairly close together.

As I previously mentioned, the engineers at Potomac Instruments seem to think it's OK to measure digital signals with an analog signal meter if the proper corrections are applied: http://www.pi-usa.com/pdf/dtva.pdf

Highdefjeff seems to think it's OK to use an analog signal meter to measure digital signals (He is talking about digital signals coming from a satellite, but the digital signals coming from a terrestrial transmitting tower are similar). To quote him:

http://www.wowvision.tv/signal%20meters.htm

To anyone who thinks that an analog SLM couldn't possibly be of any use for digital signals I say: Try it for yourself first.

As far as I'm concerned, this test proves that an analog SLM can be very useful when dealing with digital signals, which is what I set out to prove at the beginning of this thread. Or, as my math teacher used to say, QED.

Early Wavetek SAM meters are cheap. In case you come across one, here's some modification and alignment information:

http://ham-radio.com/k6sti/sam.htm

I got mine mainly for aiming FM antennas, but lately I've been using it on ATSC signals.

Brian

@ rabbit73: funny you posted that photo of your meters. They are the exact models I have, although my analog is a bit more beat up than yours, and it's some sort of CATV meter (VHF and MidBand on one knob, 220 to 450 MHz on the second).

It's a wonder for those of use that don't have a spare grand that someone doesn't make a cheap model in the $100 range.

It doesn't have to be anything but relative in readings, semi calibrated for various channels.

Seems like it might be possible to take a sample of the IF in a CECB and drive a small op amp to drive a meter or even one's voltmeter.

Wish I still had an RF lab at my disposal.

Thanks guys for all the interesting and helpful comments.

k6sti:
Thanks for posting the link for the Wavetek SAM. I've been working on a power pack idea that uses NiMH cells, and the SAM info covers the use of them.
Piggie:
There certainly is a need for an inexpensive SLM for people that are having reception problems. Outside of a used analog SLM, the best idea that I've had so far is a CECB with 2 signal bars that give signal quality and signal strength. I have done a few calibration comparisons with the Apex DT502, and it seems like a useful and inexpensive measurement tool.

73,
rabbit

Finally did my first antenna sale and got to use my Blonder Tongue FSM-11. I worked great. The house I did the installation for was at an angle so I didn't know exactly where to aim the antenna. I sold the person a Channel Master 4221HD four bay. The customer was very impressed. I got his stations from 43% signal level on his converters to 75%.

I am looking forward to trying out the Antennacraft U4500. That's the new Grey Hoverman antenna. Hopefully, it will do more than the CM 4221HD. The CM 4228HD eight bay has no more gain on the upper channels than the 4221HD. Luckily, I acquired an old style CM 4228 for my own use before they ruined it.

Good job! The proof that the meter was a big help is the jump from 43% to 75%.

I compared a 4228 with a 4221. The 4228 gave only 1 dB more gain on one channel than the 4221, the rest of the channels were about the same. The main advantage of the 8-bay over the 4-bay is its narrower horizontal beamwidth which can be a big help with multipath problems.

Thanks for letting us know how it was going for you.