I didn't think of that one Carl. CD and aluminum inside the disc might make for a good capacitor. Pretty good idea. The things you learn just playing around with these transmitters.
Turned off everything but the Wholehouse 2.0 which I set at 101.5 MHz with a 440Hz tone at less than 50% modulation. The spectrum analyzer shows 30 dBu.
It seems the worse spurious noise is spread across the low FM band from 87.5 to 90.1 MHz, with all of it being very low level according to the spectrum analyzer except 89.5 and 90.1.
89.5 had a very small bump on the spectrum analyzer, well below the required 20 dB attenuation.
The signal at 90.1, however, was almost as good as the main carrier, at 21 dBu (only 9 dB down), which should have invalidated certification.
Below the FM band there were a few spurs from 77 MHz to 86 MHz, but they were all in the low noise region.
Above the FM band there were one or two very supressed traces of the tone with no reading above noise.
It will be very interesting to learn what Tim finds with the Wholehouse 3.0.
11.4 Mhz. There was an article on one of the I hate to say it "Pirate Radio" sites. Agan I was searching for "Harmonics"+"CZH" or "Harmonics"+"FM Transmitter" and found peole talking about the CZH Transmitters and Chinese transmitters being junk because of the 11.4 Mhz harmonics. Now studying what happened with my SainSonic AX-05B (Modified CZH 05B) at 87.9 Mhz - 11.4 Mhz is 76.5 Mhz. This would have been around Channel 5 with the strongest spur. Now its interesting to note that I'm using an older TV and the TV is tuned to channel 3 which the RF from the cable box transmits on. Now keep in mind that the Whole House FM Transmitter is made from Richfield electronics. Indeed doing my research its from China. So my question is do all transmitters comming into the USA from China do this as was talked about on HB as well as Pirate Radio sites? I thought maybe it was a myth that all chinese transmitters would do this. I thought that one model may do it where as the next won't. Turns out somehow they are getting their transmitters into this country forgetting about these spurs. Here again shows why more strength on FM won't work for too many transmitters are not actually made in the USA only C. Crane and I dont know about Scoche. No wonder you see NOUO's for just a little over. Someone's TV is being killed in the low end by these FM transmitters. Again not a good rap for FM hobby Radio. Why such cheap trash? It should never be this way. I may complain to SainSonic and demand my money back if I can prove this. Or get them to fix the transmitter or send me a filter that blocks this at their expense. Just one time I fond someone in my area with a spectrum analyzer and I'm gonna pust it on youtube for all to see. They won't want that I'm sure but the people must know by solid proof if this is what is happening. 11.4 Mhz almost as good as your main intended frequency is no way to do business selling transmitters.
Last I knew the C.Crane FM transmitters are made by Sangean.
I'll check them for spurs, but I think they're clean.
Earlier I described a problem and solution to multipath interference caused to FM radio when transmitting inside the house.
At the start, most people set their home transmitter for vertical antenna operation, then discover that as doors are opened and people move about, radios go in and out of tune, giving annoying bursts of multipath noise.
In previous posts I shared the first solution I found for about 90% or more of the multipathing, namely, a Mid-Fed L Antenna taped to the wall, the intellectual property of Carl Blare, shared with members of ALPB and part15(dot)us.
While installing a second C.Crane FM Transmitter I've happened upon an even simpler solution to the indoor multipathing problem.
Set the FM transmitter within a few inches of a wall, swivel the antenna into a horizontal position facing away from the transmitter, tilt the transmitter so the tip of the antenna touches the wall, set a surplus CD (disc) under the transmitter as a ground plane (unless you already have a metal surface).
Give it the multipath test by tuning a radio in another room to your frequency and walking about the house. For me, reception is solid without multipath.
I wonder if that would help that as its a metal transmitter already. And unlike the C. Crane this transmitter at low power seems to be receivable further if you place your Radio near anything that is pluged in. I even noticed in the laundry room that if I place the Radio on top of the washing machine I got better reception of my station at low power. I wonder what would have happened if there was a close outside outlet on the porch? It probably would have been heard in full Stereo and without any noise there as well. Someone (I think it could have been Bruce) mentioned that his Decade MS-100 did the same effect and seemed to transmit along the main power of the house or apartment making it nice and clear no matter where they were in the building so long as they had a pluged in FM Radio. This could prove interesting too. If you modify the Scoche for electric operation would it too follow the power lines like my SainSonic and the Decade does?
As reported, I am now using two C. Crane FM Transmitters on side-by-side frequencies.
In the published reviews on the two versions, FM1 and FM2, the main improvement in FM2 is reduction of a noticable hum on the FM1. I can verify that this is correct.
When FM1 is operated with full modulation, the noise is far enough in the background to become unnoticable, for which reason I transmit KDX Main Channel Programming on the FM1.
FM2, with the cleaner background, is assigned to editing and auditing chores as well as audio for Youtube, HULU, and listening to WCFI.
As time advances, I have the question of whether the hum in the FM1 can somehow be reduced, and will be on alert for anyone who reports their experience.
As planned, the Wholehouse 2.0 got popped open for inspection.
The front half of the plastic case is snapped to the adjoining half by small plastic clips, 3 out of 4 of which broke off.
The circuit board is held by 3 tiny screws which came free with a jeweler's scredriver, allowing the card to be removed and viewed from all angles.
Aside from a few multi-contact chips the component parts are very tiny and all look alike, leaving me unable to distinquish between resistors, capacitors, inductors, or what-notters.
Only one chip contained an almost readable marking, the others were blank.
Trying to map out a circuit seemed un-doable, so I re-assembled it and will ban the name "Wholehouse" from the entire house.
Part 15 FM is a shabby business.
In light of Tim's findings about inter-connecting cables radiating and so causing increased RF field strength in his testing of Wholehouse 3.0, I set up this morning to analyze the two versions of the C.Crane FM transmitter with and without cables attached.
Placing each transmitter in the top center of a 30" stool located 12' from the spectrum analyzer on a 30' high desk, the first test was with fresh batteries and no external cables connected. It should be mentioned that these transmitters have an attached audio cable which is coiled to a length of 18" and can be stretched to a reach of 5'. I had this coiled into a small bundle set alonside the transmitter. Antenna was horizontal pointed away from the transmitter with the broadside toward the spectrum analyzer, whose antenna was likewise horizontal broadside toward transmitter.
The second test for each unit was AC powered with the 5.5' wall wart supplied with the transmitters.
Third test was connected to computer audio output 1.5' from transmitter.
RESULTS:
C.Crane FM1
41 dBu with batteries only
52 dBu with AC power
59 dBu with audio connected.
C.Crane FM 2
56 dBu with batteries only
58 dBu with AC power
61 dBu with audio connected.
After completing the above measurements I realized the stool is metal, the surface being a round sheet of flat cork. Point being, the stool no doubt provided a decent ground plane which most likely raised all readings by some equal amount.
The Specifications for FM2 instruct, under Audio Input Cord: "Extention cords are not recommended". There is no explanation given.
What we learned: connected wires and cables slightly increase the output strength.
I may have missed the post (many on this topic), but, in the end, with certification and education institute experimentation aside, there is just one criteria for the legal use of FCC Title 47 Part 15 FM as used by the public, which is spelled out in 15.239 (the 200 kHz refers to bandWIDTH in subparagraph a):
"(b) The field strength of any emissions within the permitted 200 kHz band shall not exceed 250 microvolts/meter at 3 meters. The emission limit in this paragraph is based on measurement instrumentation employing an average detector. The provisions in §15.35 for limiting peak emissions apply."
Having said that, there is also a very general guideline of clear transmissions of 200 ft for Part 15 radio, although the rules themselves take precedence. Part 15 AM as we know, can get out much further depending on other criteria besides field strength, but for us, FS is the only true criteria for Part 15 FM.
This means, although antenna loading and ground conductivity do have an effect on any radio transmission, you could still have other circumstances for a "FCC Certified" transmitter which could either push the intentional radiated signal beyond legal FS
Hi Ken Norris, glad to hear from you I love the "Walkie Talkie Show."
What Tim's field measurements of the Wholehouse 3.0 certified transmitter and now my simpler tests with both versions of C.Crane FM Transmitters has demonstrated is that ownership of a certified part 15 FM transmitter is no guarantee whatsoever that we are complying with 15.239.
That leaves us with NO WAY of checking our own compliance, since we obviously don't have the expensive measurement equipment.
The "200 foot rule" is way to unofficial to be a reliable guide, and it is subject to different results with different radios.
Something I brought up Carl when I first started the initiative for more power on FM. It was why I wanted to ask for 500mW, 800mW on Rubber Duck antenna. This is something tangible. Something the avarage Joe can wrap his head around. Field strength is NO WAY for a common person to even begin to make sure he or she complies even with a Certified FM Transmitter. The Rules for AM as in 15:219 is 100mW into a Antenna/Ground combo not to exceed 3 meters in length. Now that we can wrap our heads around. So in a sense the FCC has set all part 15 operators up for failure to comply with the rules. This way someone can complain about you taking away listeners and the almighty NOUO to come afterwards. So this is why we need to get the FCC to throw away the idea of field strength and allow more power maybe just under a watt into an inside antenna. That again you can wrap your head around and also gives FM some usefullness as far as personal broadcasting or short distance neighborhood broadcasting.
The comment just made by TheLegacy is the ONLY approach that makes sense!
Dear FCC;
Your cavalier gentrified jab joke called 15.239 is played out. It's gotten old. By now lunchtime drinks have worn off and you can lower yourselves to serve the (ugh) public.
SincerelyPart 15 Hobbyists of the Homeland
... it was why I wanted to ask for 500mW, 800mW on Rubber Duck antenna. This is something tangible. Something the avarage Joe can wrap his head around. Field strength is NO WAY for a common person to even begin to make sure he or she complies even with a Certified FM Transmitter. ...
Radiated field strength at a given distance is the most logical measure/limit for the interference potential of unlicensed setups legally permitted by Part 15. Interference potential is the main concern of the FCC and licensed broadcast stations.
Permitting "500mW, 800mW on Rubber Duck antenna" does not define the field strengths such systems can generate at a given distance -- when considering the radiation that can be produced by the program, power, and "ground" leads connected to that FM transmitter (FCC-certified, or not).
Tim in Bovey documented this very well by his field intensity measurements of an apparently FCC-certified Part 15 FM transmitter while using two different, calibrated FI meters -- which FI readings supported each other. NEC software evaluations of those systems produce the same conclusions.
The FCC has documented the same for the effects of such conductors attached to AM transmitters, as stated in NOUO citations issued by the FCC to operators using such configurations -- and by Internet comments that those operators were using AM transmitters having Part 15 certification.
The comment just made by TheLegacy is the ONLY approach that makes sense! etc etc
IMO, the clip above is based much more on emotion, than science.
Can anyone (including the author of the above clip) show/prove why that clip is true, in this context?