range 2 expect w/shoestringbudget stereo AM '15 at my loc?
Some time I'd like to get a part 15 AM station set up. My main question here is range (including some drawn coverage map examples) - what should I expect based on the provided linked (not embedded although I knew I could have) pics?
What setup (transmitter/antenna combo) would have the best range of what you all know of and use?
Is it possible to use more than 1 transmitter into 1 radiator? for example 5 transmitters into a single 3 meter stick would be like 500 milliwatts (100*5=500) except I'm sure there's some losses somewhere in there that I'm not factoring in. Same for the antenna - can several antennas be mounted end-to-end so the FCC will look at them as several small 3 meter antennas, but (assuming you had 5 of them) they functioned as one 15 meter antenna?
As far as frequencies being considered, they are 580 (at night there's a weak Fresno), 880 (night is a jumble), 1010 (same night results as 880), 1150 (daytime has interference from 1130 KSDO and 1170 KCBQ), 1340 (graveyard, groundwave receivable with select-a-tenna from station 180 miles away), 1490 (also a graveyarder), 1500 (there's a carrier-on-air-without-audio TIS about 8-10 miles west/northwest of me), 1570 (mostly clear midday, night has mexico, early morning once a week has a program I like to listen to (and one I'd like to relay on this station) on a barely detectable Riverside station), 1610 (has a TIS faintly receivable under best-case scenario about 12-15 miles west of me), or 1680 (fine daytime, has Fresno at night which is one of my backup stations I listen to for when KMIK and KDIS's signals are ungettable.)
Now, for the pics of coverage areas... (note that the contour lines work similarly to the ones on Radio-Locator.)
Notice the directional antenna pattern - if I used 2 (or if I can squeeze them in although spacing would be shorter, 3) vertical loaded radiators spaced at 1/8 wavelength, could a pattern similar to what's on the maps be achieved?
aerial vew #1 - small area - draw a circle the size of the crosshair, and that's the range I've gotten in the past using the cheap (not far from my total budget) Radio Shack science fair kit AM transmitters. Increase that to about where the edges of the nulls are on the blue contour, and that's the range my dad used to get with his Ramsey AM kit which (as far as I know) he still has.
aerial view #2
aerial view #3 - the two main north/south streets to the west and east of the transmitter are each about 1 mile away.
aerial view #4 - I'd guess this to be 2 miles in radius if it was non-directional (going to edges of the map). For those of you that claim a 2 mile (or similar) range, do you mean the signal is just barely detectable using a $25,000+ military-grade receiver and multiple beverage antennas, or is it comparable to this short clip recorded with a Sony SRF-42 and Select-A-Tenna at around 8: of KDIS 1110 while going along Longden Ave near Myrtle avenue, and turning onto Live Oak ave. in Baldwin Park, CA (west of I-605 between I-10 and I-210)?
aerial view #5
aerial view #6
aerial view #7 - if it was possible, this is the daytime coverage I'd like to be able to have
map view #8 - here's a map (zoomed out some) to give you somewhat of an idea of transmitter location and surrounding area. What's the ground conductivity like in my area? (note there are no closer zoomed in maps.)
aerial view #10 - if skywaves improved my signal at night (chances are slim to none though :() this is the coverage I would like to be able to have (assuming SRF-42 and select-a-tenna at outer contour (wishful thinking).
map view #11 - I'm not quite sure, but I THINK the blue contour on aerial #10 is about where the purple contour on this one is.
we can dream, can't we? (daytime) - my "dream" daytime coverage, assuming I had the same pattern. Actually I'd want to turn the pattern clockwise so the main lobe is centered on Sacramento.
we can dream, can't we? (nighttime) - my "dream" nighttime coverage - just rotate the pattern so the main lobe is centered on the line between two imaginary lines - one from the transmitter to Ft Worth, TX, the other from the transmitter to Oklahoma City, OK.
Being reasonable, what should I expect from various types of setup?
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While I'm here, anyone know how to receive KDIS with a signal comparable to this from near where my proposed transmitter site is? It was recorded about 10 minutes before the other KDIS clip above with the Kung Fu Fighting song (I was at a friend's house about 1/2 mile west of the intersection of Longden and Live Oak mentioned above.) I have a Sony SRF-42 and Select-A-Tenna, but I'm getting lots of interference from 1130 KSDO. 🙁
Some time I'd like to get a part 15 AM station set up. My main question here is range (including some drawn coverage map examples) - what should I expect based on the provided linked (not embedded although I knew I could have) pics?
What setup (transmitter/antenna combo) would have the best range of what you all know of and use?
Is it possible to use more than 1 transmitter into 1 radiator? for example 5 transmitters into a single 3 meter stick would be like 500 milliwatts (100*5=500) except I'm sure there's some losses somewhere in there that I'm not factoring in. Same for the antenna - can several antennas be mounted end-to-end so the FCC will look at them as several small 3 meter antennas, but (assuming you had 5 of them) they functioned as one 15 meter antenna?
Hmm. I think that either of the above would put you outside of the part 15 Rules. But, you know what? If your really just a hobbiest you could experiment with these ideas. I'm afraid you'll find them disappointing unless your well versed in antenna and or transmitter phasing. Getting 5 transmitters on the same frequency to operate in sync with each other, though not impossible, is not easy. Especially on a shoestring.
Your range is, as I'm sure you've read in other posts, going to depend on a lot of things. I didn't look up your conductivity. Being stationed on the naval base there I remember lots of sun and very little rain. I'll guess 4 to 8 mho. So your ground system is going to be very important if not crucial. I'm assuming that you've got a lot of room for a good ground system
The part 15 antenna that WCRV can build for you, or that you can build yourself with plans fron the sstran website. Is a very efficent and legal means of getting your signal in the air with a 100 mw transmitter.
At least 1 transmitter that works with this antenna is capable of transmitting at a power higher 100 mw "where allowed". I am not going to suggest that you transmit at a higher power then whats legal, this is piracy.
Your coverage maps are interesting.
Sounds like some interesting ideas there.
The photos are helpful, because the location of the XMTR, in relation to the concentration of listeners, certainly shows why you might be a bit frustrated.
Most low power efforts try to locate the XMTR as close a possible to the listeners - any way you could broadcast from a different location?
All your ideas sound interesting, though it's tough to see how it would all come together. By all means expeirment, and report back if anything surprises you. There are some pretty tough technical issues to overcome, though.
Low power AM experimenters are rarely enforced against, unless you're advocating sedition or really being obscene, but the FCC agent would probably smile if he or she did come to visit and saw a 50 foot antenna with five 100 mw units pumping into it. I mean they do say you can use up to five XMTRs and that implies five antennas 8) I'm sure one of our more technical visitors could tell us why that would probably be specifically prohibited, but it's an interesting interpretation!
I can't envision how a 3 meter antenna array could be configured to be directional. Theoretically it might be possible to model, but wow, that would be some precise placement and tuning 🙂
A sloper would definitely work, but would need to have a very tall vertical element.
If you have the room to erect a full size horizontal array there are people who say that works, but each element would be over 500 feet long if you worked the high end of the dial, and I think the whole array of three elements would be over 1000 feet back to front. There is a pretty specific prohibition against being directional when radiating under part 15, but again, not too much scrutiny on the AM band.
Sky wave never favors the low power stuff, we just get squashed by everyone else. Some of us don't even think about coverage after sunset, and just leave the XMTR on because it's easier.
Some broadcasters operate multiple XMTRs and link the audio over the internet, so you could find four like-minded people with broadband internet and set up a unit in each location and feed the audio from a central location on the web.
WiFi has also been suggested as a possible link for distant XMTRs, and there's some pretty interesting stuff going on with long-haul WiFi. I think some guys just did an absolute max legal power level WiFi distance test in the Nevada desert using hand made directional antennas, and they went over 50 miles.
For real wide area coverage, but probably no listeners, you could try part 15 shortwave, described here:
http://home.att.net/~weatheradio/part15.htm
http://home.att.net/~weatheradio/HFtransmit.htm
Hi!
I think the biggest problem with using part 15 transmitters for a directional array will be the phasing. You're not going to get the response or coverage you want by using multiple radiators with separate transmitters. There's just no way I can think of to control the phase of the subsequent transmitters. Commercial directional stations generally use one transmitter and a phasing array for each additional tower (which may consist of nothing more than a specific length of coax going to the next tower and that's going to put you over part 15 rules on antenna length). That way they have control of the directional pattern. For instance if your second antenna was 180 degrees out of phase with your first antenna's signal when it arrived at your second antenna there would be little or no signal transmitted in the direction of the line of antennas. It is complicated, but unless you have a way to reliably sync your multiple transmitters I don't think you will end up with a consistent coverage area. You might try a passive elements and get some directional results, but they probably won't be impressive.
There's just no way I can think of to control the phase of the subsequent transmitters. Commercial directional stations generally use one transmitter and a phasing array for each additional tower (which may consist of nothing more than a specific length of coax going to the next tower.
Ah! A ray of insight! A length of coax to delay the signal is a very precise way to control the phase to each antenna. Phase locking multiple transmitters via GPS or even direct wire is not likely to yield the exact phase relationships required.
Phil B
Got a Question
How come you want to direct your signal away from all those cluster homes to your sw? I think it's sw, whatever?
I don't see you using 5 separate tx's on your system. How would you phase them with out causing distortion and generating spurs and harmonics.