I spent nearly 3 hours out in an open field yesterday running tests on the Whole House 3.0 transmitter.
I purchased this transmitter at retail from a seller on Amazon, so what I tested was one as sold to the general public, not one handpicked by the maker or importer.
Tests were taken with an accurately calibrated Potomac FIM-71, the same as the units used by the FCC in the field, and also used by most broadcast engineers who need to do work with FM broadcast stations. The readings then were also taken with a ZTechnology R-506 which is used by a wide variety of RF engineers in dozens of applications and is also the "new" technology often used by the FCC for tracking down illegal operators because it can output to a laptop and also synchronize with a GPS unit and compute exact field strength from varying distances, etc. Needless to say I just use mine for manual field strength readings. BTW, if you were to buy a new R-506 with its calibrated antenna the price is $13,000. Each device was used with it's own calibrated half-wave dipole antenna. Antenna factors were applied as appropriate, as well as cable loss, etc. All readings were so close between units the differences were negligible.
Documentation on this very forum has shown FCC documents where these exact devices are used and referenced in filed complaints.
The test site was a large open field. The nearest building as at least half a mile away, the nearest trees were many hundreds of feet away. The Whole House transmitter and the FIM-71 receiving antenna were at 7 feet above the ground as specified by Potomac. It is worth noting that the receive antenna on the FIM-71 was horizontal for all tests (it's a half wave dipole adjusted in length for the frequency) as this is what it is calibrated for, I did however take readings with the transmitt antenna both vertical and horizontal. You will see that, at least at 3 meters, antenna orientation has a huge effect on signal. I am posting all readings in uV. You may convert to mV if you like. I was testing at 92.7 MHz, the frequency that showed a nearly imperceptable reading of background noise effect, somewhere around 1.5 uV/m (so technically you might subtract 1.5 uV/m from my numbers but it really won't matter.
Here are the results, followed by some more comments.
At three meters, transmitter in "US power setting":
With Transmitter antenna vertical: 382 uV/m
With transmitter antenna horizontal: 1102 uV/m
At three meters with transmitter in "Canada power setting" (lightning bolt icon showing)
With transmitter antenna vertical: 4950 uV/m
With transmitter antenna horizontal 17775 uV/m
There are your basic tests at three meters between transmit and receive antennas. I then did a quick range test using the Tecsun PL310 as long as I was in an open area. I didn't have the ambition to run a marathon to various points so I went out to 220 feet. At US power at 220 feet signal was readable only by positioning the radio for the "hot spot" where the signal was strong and clear. Now, this was directly broadside to the transmit antenna in a horizontal position. As I walked around so I was at an end of the antenna (e.g. with the transmit antenna pointed at me) the signal was gone by about 100 feet. So in horizontal position, as expected, the signal is quite directional. The above tests were all done with just the transmitter on, running on new alkaline batteries, with no other cables connected to it. But I noticed something a couple weeks ago while playing around with this transmitter out in the yard that I was curious to test out here in the open.
Apparently connecting any cable to the transmitter increases it's RF output. I'm guessing that connecting, say, an audio cable to the line in jack, the common (ground) of the audio cable acts as a counterpoise to the antenna, as there's quite an RF output jump just by simply plugging in an audio cable. Per haps it's one of the other leads in the cable acting as additional antenna, I don't know. And it also seemed to somewhat negate the effects of the horizontal or vertical antenna. With the FIM-71 reading 382 uV/m with the transmitter in low (US) power and the antenna vertical, I plugged in a 4 foot audio cable -- 1/8 inch stereo to 1/8 inch stereo, and the output jumped to 4050 uV/m and this is just with the audio cable hanging down from the transmitter. I was able to vary the output greatly just by changing the position of the audio cable in relation to the antenna. I then tried it with the external power cable. This is a short USB power cable provided with the transmitter. Same effect, except not quite so dramatic of an increase.
Then I though, what might the field strengh readings be at 10 meters? In high power, the secret "Canadian" setting, with the antenna horizontal it was 11475 uV/m. Switching it to low "US" power the readings at 10 meters were 360 uV/m with the transmit antenna horizontal, and 112 uV/m with the transmit antenna vertical. Just in case you're curious, with the provided long wire antenna (that has the warning not to use it in the USA) the field strength went to 17775 uV/m in the high power Canadian setting. Although I wasn't really prepared to test this as I had no way to hold the antenna wire in the air so I just let it hang down from the transmitter. Also as it was a breezy day the field strength varied as the antenna swayed in the breeze. Had I been thinking I could have plugged the audio cable back in to see what I got! Probably if the antenna were held up above the transmitter and the audio cable was straight down as a counterpoise I could really have had some power going!
My conclusion has to be that there's simply no way this is legal in the USA. Although, it's certified. Makes me wonder exactly what the certification process involves. Now, the Potomac FIM-71 indicates the margin of error for these tests at 7 feet above ground level is 18%. So, in US mode, with the antenna vertical, and no audio or power cables plugged into the transmitter the reading is 382 uV/m. Allowing an 18% error in favor of the transmitter being legal (FCC documentation on this site shows the FCC always factors maximum margin of error in favor of the station) that still leaves us with 325 uV/m which is still above the limit of 250 uV/m. Then again, the margin of error could easily go the other way and be 439 uV/m, or somewhere inbetween. Whole different ball game if you flip the antenna to horizontal. Then it depends on if you're reading off the null ends of the antenna, or broadside. I didn't take any null end readings but I'm sure those readings would easily be legal.
Then, just for fun I took the transmitter up to my studio (second floor, old wood house, easily 20 feet above ground level) and set it in a window. Then I set up the FIM in the backyard. I was just sort of goofing around here so I didn't take any real readings, I just wanted to be able to see relative changes in field strength, but I was completely amazed at the HUGE difference in signal strength that could be induced sy simply plugging in the audio cable, and the differences between plugging it into an iPod compared to plugging it into a CD player (RF was quite a bit higher plugged into the iPod than a CD player). Or how simply moving the transmitter a foot to the left or right, moving the antenna to various positions horizontal, diagonal, vertical. Setting my wire glasses next to the transmitter even made a difference. I tried probably 20 different things. Moving the transmitter, moving the antenna, setting different things next to it, plugging it in to the ipod, then the CD player, moving the cable around, etc. Every thing I changed changed the field strength. Now, clearly I could have been simply been changing the direction of the signal, as well as varying the output by providing a counterpoise. I finally quit because I had to run up two and a half flights of stairs from the studio out to the backyard and back and I got pooped.
Trying to predict results, effectiveness, coverage, etc from this transmitter, and I suspect all Part 15 FM transmitters is a shot in the dark as a countless number of variables will effect virtually everything.
So of course now I can think of a thousand different test combinations, but I'm done with this transmitter now. So if anyone would like to buy a slightly used Whole House 3.0 at half price let me know 🙂
It will be interesting to see what the Decade CM-10 has in store for me.
Tim in Bovey
Tim - The results of all your work in the OP are important information, especially given your long-term broadcast background and your use of the FIM-71 and R-506.
I may have further comments after I fully digest what you posted, but not as relate to the fields you measured.
Much appreciation to you Tim for measuring the Wholehouse 3.0 in such detail.
In one way your results might make some members want to own a WH 3.0, while at the same time making them wary of getting "caught."
Did you happen to check for spurious output in and out of band?
Recently I posted a finding that the Wholehouse 2.0 puts out a lot of junk in the area from 87.5 to 90.1, plus some spurs elsewhere, one of which was NOT 20 dB below the main carrier and therefore renders my transmitter in violation of 15.209.
Sorry, I didn't do any testing for spurious emissions, etc. The thought had crossed my mind, but by the time I got done the standard field strength tests I was pretty tuckered out!
I hope to do the same tests with the Decade CM-10 in the next couple weeks. I'm up to my eyeballs in work this week and then we're off to Marshalltown, Iowa where my Son and I are autocross racing our 1964 Corvair. So at best next week sometime.
Tim in Bovey
TNX Tim. It looks like you had fun. I would be interesting (not on your dime) if there are manufacturing variations with regard to power.
Yes. I was wishing that I had a box full of these so I could try them back to back under the identical conditions and see if there were any significant variations. And I'd hate to try any that didn't come from retail sales, brand new. Used ones could have suffered some damage some way and loaners or freebies from the makers etc could be tested before shipping. The packaging was easy to open then return to the package like new.
TIB
Really appreciate you taking the trouble to do this....thanks.
Surprised to see that out of the box in it's certified state with "regular" power and stock antenna it's 1 1/2 times the what it "should be".
Very interested in the CM-10 also....
Thanks again for doing this!!
Adding audio cable and maybe using it with A/C power would increase the field strength because it's like adding antenna....makes sense.
The set up procedure for the certification can be looked up.....wonder if it was done on batteries or with A/C and micro usb cable. Also surprised that the antenna vertical was less than horizontal!...maybe the majority of the radiated signal from the length of the antenna was more concentrated with the meter in front...but maybe "dead spots" if you were out from the end of the antenna.
Mark
Also surprised that the antenna vertical was less than horizontal.
Just to note that the field arriving at a receive antenna can be reduced by 15 dB (or more) when the maximum E-field polarizations of the transmit and receive antennas do not exist in the same plane.
I suspect that the polarization difference may not be as dramatic over a longer distance.
Not only is there the polarization difference, but a dipole is quite directional on the broadsides, and even though the transmitter antenna isn't quite a dipole I assume it's working off a spec of something inside the transmitter -- something that the audio cable or power cable connects too (ground?) thus creating a nice counterpoise for the antenna.
TIB
In case you're wondering what the Z Tech R-506 looks like. Not a very big device, but packed full of smarts. it's really designed to be carried in it's case over your shoulder while you use either the small "utility antenna" that mounts on it, rubber duck or small telescoping, for taking relative readings, or using the handheld half wave dipole (similar to the one on the FIM-71) which can also be mounted to a tripod or other support as needed.
Anyway I took a quick shot of it so you can have a look.
TIB
So it would be difficult to decide on your polarization fro your transmitter. What do peoples receivers have? Most cars are vertical, some have horizontal in the windshield. many clock radios, table radios, etc use the AC cord, or even have a wire hanging out of them for the FM antenna. But if you opt to go horizontal your signal becomes quite directional in two directions and much less in the other two directions.
My determination was this FM jazz is pretty fussy stuff. I think if you were trying to do FM perhaps the best choice would be up on a wood pole in the clear someplace. Lord knows what would happen if you had 50 feet or so of power line and audio line!
TIB
Tim, I take special notice that you have observed the audio shields and power wires acting as part of a ground plane.
It brings to mind the inductors that I see on the audio shield and power input of the C.Crane FM1 Transmitter, which I have assumed to be RF filters intended to avoid the ground plane effect.
You haven't mentioned having the schematic to look at for the WH 3.0, and I found that the schematic for WH 2.0 is not posted with certification docs on the FCC site due to a "confidentiallity letter." But the C.Crane schematics are posted on the FCC certification site.
for tim, the readings you got come as of no surprise to me. that company has a shady history and has been slapped by the FCC more than once.
they probably sent in a couple test specimens to the FCC lab that passed muster to get the certifications and then said screw it and upped the power on their production units.
given the history of this company it would not surprise me to find this is the case and if the FCC truly does read this forum i am sure your findings are right now making their way through the chain of command and the fcc will likely buy some retail units and run their own testing. look for TAW Global to get slapped again by the FCC.
According to this document:
https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf
The FCC or it's lab may never actually see a transmitter before it's certified. The necessary documentation and testing can be done by any outfit than can demonstrate they have proper equipment and facilities to complete the tests and compile the needed report.
TIB
Thanks for the time you took to do those tests Tim.
I'd be interested in seeing some results from the Decade MS-100.
My network used those, we did however attach an indoor VHF television set top diople antenna (rabbit ears) to the factory attached verticle antenna to make our signal horizontal. The two sticks were tied together as one and positioned in a horizontal position. Just letting you know that we did not attach one stick to hot and the other to ground.
The transmitters were designed to service one large (Multi Floor) apartment buildings where the intended listeners were all in the same structure above and below and level with the antenna system (same floor level). The audio feed was sent by me via the Internet.
Other than using portible radios for checking signal coverage by ear, we did not have any calibrated equipment like an FIM 71 to determine field strength.
I am curious why we were the focus of being acused by another part 15 related site as broadcasting as a pirate station. I mean what field strength could any one of those transmitters been generating that cause all that fox hunt and other related crap to be thrown at us?
I mean besides the mod to transmitter antenna to be horizontally polorized, we did nothing to the transmitter's internals besides adjusting the output frequency.
Bruce.