I am curious, (usually all the time,lol) i have been using my SSTRAN on 800 khz wired into the shield side of 60 feet of cable t.v. coax. Which makes me wonder about whether it is transmitting vertical, horizontal or both? I am almost but not completely convinced that it is horizontal and here is why i think this.
The cable is tucked in between the mobile home and the vinyl facing right above the under pining. (hard to explain and it’s raining so no pictures). Although the cable is horizontal , the signal does manage to radiate at least 50 feet give or take away from cable. After that it just drops off rapidly on a car stereo.
Am i right in thinking this?
Coax
Actually your TV coax is not leaky coax.
In fact, you cannot make a leaky coax out of an ordinary coax wire.
Basically this means your TV coax is killing your potential range, you need to buy an actual leaky coax.
Man made interference is Vertical, so in theory horizontal polarization would be the way to go. But most car antennas are vertical. as are most radio antennas.
Cable Service?
rock95seven, is your cable hooked to cable service? If so, then the shield is grounded probably at your service entrance and also out somewhere on the pole or where-ever it is fed from.
Otherwise, the cable you described is horizontally placed, so you are radiating horizontally, I think, but a horizontal signal will pick up on a vertical receiving antenna……as the polarity on the AM band does not seem to be all that delicate.
Even on FM a vertical C.Crane telescoping antenna gets picked up in the other room on a mostly horizontal receiving antenna.
Even PhilB, if memory serves correctly, described his basement setup where his antenna is horizontal because of limited vertical space.
A Wild Thought
Re-Reading all of this, it suddenly came into the head, that if your cable coax contains actual cable, wouldn’t it be insane if your radio transmission is getting inducted into the cable and reaching radios located near other people’s cable maybe over a ten mile area?
Has anybody ever investigated sending AM signals over area cable, with of course, the agreement of your service provider.
I Never said it was actual leaky cable but
since the shield is meant to be used as a ground and is closer to the outer protective jacket it will radiate, perhaps not 100% of the rf applied but it does radiate as i mentioned 50 to 60 feet from the house.
(and being cheap aluminum shielding too)
It is not connected to any cable tv service and is only meant to service the house as a separate radio service from Rock 95.7 fm. The only other house it might serve is my neighbor directly behind me a mere 13 feet.
That fact it radiates 50 feet from the house is amazing though not intended i am surprised it works that well. My mobile home is probably 70 or 80 feet long so the length of the cable is probably more than what is needed to radiate a enough signal evenly around the house and apparently out past my yard. I do not have enough room here for ground radials but i do have a vertical ground plane for Rock 95.7 fm mounted outside on the front porch. I have not used that groundplane in over a year. I find that the whip antenna provided with the Ramsey FM 25b is enough to cover 200 feet near field and 900 fringe so I feel that i really don’t need that groundplane.
Carl,
That would be a cool way too cover several miles…
250uV/m @ 3m
Ill chime in….
..using the ground side of tv cable, attached at the service drop or not, will have to meet the 250uV/m @ 3m limit, even though the signal may travel down the ground shell of the feed line hanging on the poles that runs all over your area.
It would follow the same concept as MW carrier current, though MW carrier current at the low end of the band allows for 15uV/m @ 30m 150k/f=distance in feet from wire.
In the case of the FM band, well it does not matter what the frequency is, or length of cable or coax feeding an antenna..the limit is the same through and through…..250uV/m @ 3m from the radiating element..be it an antenna or leaky coax or ground shield of the tv cable coax and feed line on the poles.
Given that VHF frequencies will be quickly absorbed by the cheap aluminum shielding within the jacket of the cable as well as the aluminum shield around the main feed line hanging on the pole, it would take a bit of RF power to send the signal “down” the line…problem is that the signal wont just get a boost to travel “down” the line, but also a boost radiated “off” the line…ie increase in radiation off the line, and no doubt will exceed 250uV/m @ 3m.
A leaky coax designed for this would serve the purpose better, and keep you within the field strength limits.
Then of course there is the ever changing inductance due to temperature and environment conditions which will shift the loading on the transmitter, which can make things worse or even help depending on which way things go.
RFB
Either way it works
The fact it works at all is amazing in itself considering it isn’t true leaky cable. And since i just want to keep the AM signal very very local the coverage is enough for me. The FM can serve the mobile homes and a few apartments as it has been doing for 4 years nows. The 800 AM station can serve my home as a more private signal.
Nothing i air on 800 AM is offensive it just doesn’t fit into the Classic Rock genre i have been airing on Rock 95.7 FM. Occasionally i can pick up Rock 95.7 about 1/4 mile away from the house when it is cloudy or overcast. Otherwise i can’t hear the FM after I leave the mobile home park i live in. It is a very tight localized signal and stays as legal as possible with the whip antenna on my Ramsey transmitter.
This park is a challenge for any one wanting to broadcast with flea powered transmitters especially on FM, all the metal around here causes all kinds of reflection and there are places my signal will not reach. The rental office is tucked into a small corner in the back of the park so getting a signal to that corner would take an antenna up higher than what is allowed by park regulations.
The apartments can probably hear my FM if the listener is living in the apartments facing my home, that would be line of sight, anything on the other side of the apartments would have hard time receiving the FM since the buildings facing me block the signal and the rest of the apartments are in a lower area. It is hard to convey in words the lay-out of this park. I am in a high area, below me to the Northeast is the lower end of the park and next to that area is the apartments at the same elevation.
The Northern section of the park is surrounded by a hill, to the south and south west is hilly so this whole area here is a challenge.
Rough coverage map
Just to give a general idea of what kind of coverage my Ramsey Fm 25b is capable of with the whip antenna inside my mobile home. The transmitter is sitting on a desk in front of a window.
The green circle shows of course the best reception but keep in mind the other homes tend to throw the signal in different directions. Some picket fencing happens often.
I used Google Earth to map the distance. Green is 200 feet the last outer ring is 900 feet and the signal pretty much comes and goes. I am sure the scale is changed a bit since i cropped the image.
http://www.radiodizzy.org/covers.jpg
P.s. I would have created a coverage map for the AM on the not-so leaky cable but whats the point? it would just show an outline of my home lol
Range with Ramsey
That is just about right for those types of transmitters. The 100 and 100B cover the same range when using the supplied whip.
Have you tried experimenting with the AM for Carrier Current? Then the coverage map could quite possibly extend to the entire area of the mobile home park…perhaps even beyond that into nearby neighborhoods.
I see an excellent opportunity to the right on that coverage map….if it is indeed a shopping center. Oh boy…do I see an opportunity just waiting to be tapped!!!
RFB
There is a lot of potential
RFBurns,
The most i have achieved with AM is with a T.H. with the wire antenna, oddly enough it was able to transmit out of the house and up to 1/4 mile and would pop up at major intersections around town where there are many power lines intersecting each other.
I have wondered what CC AM would do here with most of our power lines, cable tv and telephone buried underground. The only visible utilities are the lines coming into the mobile home park off of hwy 1006. They come into the park then stop across from my home and go into the ground by conduit. There are transformers on the ground serving a handful of homes per transformer( at least that is my guess ) It would be interesting to see how a neutral fed CC would do under these conditions, however i do not have a CC transmitter or coupler.
CC is something i had considered for a long time given the trouble i have been having with FM and all this metal around me. The reason i have not tried building a 3 meter antenna for my SStran is the lack of space to bury ground radials. Since gas and other utilities are buried here and the strict rules in this park regarding antennas i just opted for running the AM on a 60 ft cable.
Considering all the metal, i can actually hear the FM right up to the entrance of the park, as soon as i turn off Reams Ln onto hwy 1006 the FM drops out completely as if someone turned the transmitter off.
Edited: Actually RFB, that is just one of the shopping centers, there are several up and down hwy 192 for a couple miles then after that on each end of hwy 192 is a few stores here and there but mostly residential areas. Across from I-75 is Subdivisions and a new hospital.
CC and Underground Utility
I have done some extensive tests with various transmitter types for CC, after I optimized my CC system, which can be viewed on the KDX website for the program LPH (Low Power Hour)..episode 4 is it? Wow its been awhile!
You mentioned the TH unit. If you have not heard the latest episode of LPH, episode 13 (oh what a coincidence eh! ;)..)
I am currently developing a coupler device that simply plugs into the external antenna port on the TH at one end, and the other plugs into a standard household grounded power outlet.
I am basing this design on the LPB TCU-30 coupler, though my coupler unit will not have the fancy 20 step induction and 15 step capacitor cancellation circuity. The reason is that in my testing I found that there are 3 points along the inductance correction and neutralization through the capacitance decade to make this new coupler in 3 different versions. That is to say, taking also the approach that LPB did with their CC transmitter’s low pass filters on the final power amplifiers, they split the AM band into 3 segments, 530-830Khz, 840-1280Khz and 1290-1710Khz.
The goal is to create a way for expansion of existing Part 15 stations as low cost as possible. It also will provide a way for a beginner to easily and inexpensively begin a Part 15 AM station without the trouble of building antenna systems and all the other issues involving intentional radiators.
It is not intended to replace or knock out intentional radiator setups or give them a bad name. In certain situations an intentional radiator system would be a better choice due to either limited access to a power coupling point, or for those unique setups where the TX setup is powered by battery/solar panel/wind generator etc.
As to underground utility lines, I have found this has no effect on the system. Why? Well for starters, we are not trying to radiate our signal “OFF” of the power line. We are trying to “PUSH” our signal “DOWN” the lines length as far as possible so that it reaches as many power outlets in homes and businesses as possible. Our signal will be fed right into the listener’s radio via the power socket rather than the signal being picked up through the air. Buried or not, the signal will get to the listener’s receiver via “Wired Wireless” approach.
Here is a list of transmitters tested with my coupler design so far:
TH 5.0
Ramsey AM-25 (100mW mode)
Panaxis AM-100
This next one will make everyone laugh..but it performed well even to my surprise…
Radio Shack AM Broadcaster kit (circa 70’s) and two Radio Shack electronic lab units (150 in 1 and 200 in 1 sets)
All gave the same performance in coverage, roughly a 4 block area.
I will keep everyone updated on this as I am sure this is peaking everyone’s interest. 🙂
RFB
Imagination gives way to enginuity
RFB,
Your design sounds fascinating and yes, you’ve peaked my interest. I am one of the many who are in a unique situation where a intentional radiator is not possible.
Though i have mentioned i have a ground plane up for my FM, i hardly ever use it due to the height limitations imposed on renters here. The rule is simple, sort of.
Renters can have antennas here, but they cannot be higher than 3 feet above the mobile home. Obviously they don’t want renters installing something that is too big for fear of it falling down and possibly hurting someone or causing damage to the property. Though the maintenance guy told me it was to cut down on RFI, i informed him it was possible for a totally legal un-tuned 4 watt c.b. to cause RFI even at those heights.
My ground plane met their approval. But as far as digging up the ground around the house, that is one thing they informed me would not be happening. There is just too much stuff underground here to take that kind of chance. Heck our flower beds are 10 feet long and 1 1/2 feet deep. lol
That’s were CC would come into play, using the power lines as a way to get past the limitations here would be ideal and since i would not have to bother maintenance with installing a coupler to the breaker box makes it even more viable. I am sure others are interested as well and i will stay tuned for more info as you refine the coupler. That is a great idea. Keep up the great work.
Imagination Giving Way
Rock95seven triggered my imagination when he mentioned his flowerbeds. Perhaps there are ground solutions that we can invent which are sort of “trojan horses” because they are secretly grounding elements.
The first thing I’m thinking about, the neighbor marked off a huge strip of his yard with some kind of metal “edging” that looks like a little “mouse fence” that is half buried, half raised – about the height of a shoe – and contains the planting area. Maybe we could be fancy and have “radial gardening displays,” just like the big-time botanical gardens.
It would be a grounding system hidden in plain sight.
The ten-foot pole in the center of the garden could support a bird-house “top hat.”
hmmm
That could be done Carl.
I never even considered something like edging to take the place of grounding elements. The only thing i would be worried about is the 10 foot pipe being 1/2 a foot away from the metal siding on the house.
It would surely make the signal directional. All the flowers have wilted already from the several weeks of extreme heat. Now after 3 or 4 days of rain, the soil is damp again, the yard is still crunchy but it is slowly turning green again.
I could place the sstran in a good sized tupperware container, place a wooden stake at one end of the 10 ft pipe and drive that into the soil. Wire a coil to the pipe and hope for the best.
Leaky Question
I got to wondering, how is the grounding managed on a leaky cable AM system?