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Antenna Amp as RF Amp?
Hi All. Newbie here (although I did work with Part 15 FM a long, long time ago when 100mw was the legal power output – and FM stood for Find Me!)
I am curious with a dumb question on RF amplification.
Is it possible to attach an antenna amplifier (like the Radio Shack 15-1009, whose spec sheet is limited but “boasts” up to 30 dB amplification) to the antenna output of a low powered IPod style FM transmitter, (like the C Crane FMT or the Belkin TuneCast II)? Or would the relatively low power of the transmitter fry out the amplifier?
(Never mind about the potential non-technical issues with using this to boost power past Part 15 limits….) Right now I am just trying to get my tunes strictly for my personal use across a 20+acre property and the signal is not meant “for public consumption” outside my property lines.
Thanks in advance for your wisdom and insight.
Total posts : 45366I didn’t find the 15-1009 on the RadioShack web site. Is this the correct model number?
Total posts : 45366I ran a V.C.R. into one and connected it to a homebrew dipole and could see Channel 3 for around 300 feet! Never tried it for FM but I’m sure it would help..
Total posts : 4536612v – I had read that it was possible to do that, I just never tried myself. I actually went running around the house the other night looking for a VCR (we’re still unpacking), and couldn’t find one to try this with.
Thats actually pretty cool – I wonder if it’s legal in the FCC’s eyes? I mean – it’s not like you went and bought an amp 🙂
Total posts : 45366Hi gang,
Thanks for the responses. Maybe my questions wasn’t so dumb after all and you can noodle on this a little more…
First, I apologize for “fat fingers” here. To correct and clarify the first post, the correct Radio Shack part number is
15-1109
It is called a
TV-FM Antenna-Mounted High-Gain Signal Amplifier
and here is a link to its tech support page, with all the manuals and published specs:
I checked the web site and my model does not appear as an available item. (I bought one on clearance, but not long ago.) The following appears to be an equivalent replacement:
15-2507
which is now called a
TV/HDTV/VCR/FM Antenna-Mounted High-Gain Signal Amplifier
and here is its link:
The 15-1109 seems to have more documentation on line than the 15-2507.
We have what appears to be a similar unit by Channelmaster, which is combined with a very large (50++ elements?) Channelmaster roof top antenna which brings in our “local” broadcast TV channels pretty clearly from over 65 miles away. (We have line of sight up on our hill, our neighbors below do not.)
What occurred to me before trying (and maybe frying) this thing out as an FM RF amp for one of those low power (8-10 mw) FM “iPod-type” transmitters (C Crane FMT or Belkin Tunecast II) is that the input signal that is coming into the RF amp for TV is very weak, but I have no idea what the ballpark number of millivolts or microvolts or milliwatts coming into it is from the TV antenna (I suspect a really low number) or what the “Pod-Casters” put out in terms of millivolts or microvolts or milliwatts. The specs that I found on Radio Shack’s website are not specific as to maximum INPUT power, which is usually a key spec for any amplifier.
I was hoping that maybe there are some RF or other gurus out there that may know whether this is ok to try or whether I am about to fry out a $60 amplifier. Or maybe someone knows some ballpark numbers to help me try to piece together some of the puzzle. I am just a little reluctant to try this experiment without some guidance…
Many thanks.
BTW, while you may want to set up a separate thread for “Part 16 1/2” TV, there is “professional” stuff out there to amplify antenna signals and distribute it around the house. I don’t know the vendors offhand, but the pro installers use sources other than Radio Shack… Also, if you want more choice than the Channel 3 output of your VCR, Cabletronix (and others) make UHF-TV Modulators. In our house the TV antenna guy installed a Cabletronix CTARM-2LT which takes the output from 2 separate DirecTV receivers and puts them out on two separate Channels (he picked 38 and 40, based on free channels around here, but you can pick any you want). Any TV in the house plugged into our cable can receive the two Sattellite receivers on those channels plus the over the air channels from the roof top antenna on whatever channel they are broadcasting on. Presumably, if you could take an antenna amp and make it work off your VCR, you could take a UHF-TV modulator and plug it into your antenna amp and an antenna wire to have an opver the air broadcast for a limited distance as well.
Total posts : 45366
Total posts : 45366My $0.02…
My first thought about “oomphing” that FM signal out across 20+ acres:
How about “oomphing” the antenna? 20+ acres should mean the neighbors aren’t exactly next door to complain.
What’s the layout and where are you in it?
In the center? What about a 5/8 wave groundplane vertical? Or maybe a 2-element collinear folded dipole?
At an end, or a corner? How about a “Flying Vee”? Maybe two fed side-by-side to cover a larger spread? In the middle of a long, narrow lot? How about two Flying Vees back to back? See “Single element beam antennas for Part 15 FM” in the Part15.US Library.
Hey, it’s a thought…
By the way, RadioheadC, thanks. I thought that Part 15 FM used to have a 100mW/1meter standard. Apparently I’m not the only one.
Total posts : 45366Ok, here are my comments.
The RS amplifier is intended to amplify very weak signals to a level that is acceptable for a TV receiver. The amplified output level is very low (because modern TVs are already very sensitive). Driving the RS amp with a transmitter will grossly overload it unless you attenuate the transmitter feed. The output of the amp will be very low (within the range of a TV’s antenna input). Not very promising! Your transmitter alone will probably go farther.
However, the reply about CATV distribution amplifiers has some merrit! These amps are probably offered over a broad range of power outputs. The higher powered ones would be designed to drive a very long coax run terminating in a large number of destinations. The power output would be sized to produce a good signal after all the huge losses. This type of amp seems be the best bet for really boosting power to cover a large area. You may still need to attenuate your transmitter output feeding one of these, but the radiated signal should be good.
Total posts : 45366tregonsee:
Excellent point! A really good antenna can go a long, long way toward improving range.
The problem boils down to how to match the output of a C Crane (or whatever) to a good antenna. You would need to reverse engineer the transmitter output circuit to determine how best to add a good matching circuit.
Total posts : 45366[url=http://store.qkits.com/moreinfo.cfm/qk171][size=12:f86d99735b][color=blue:f86d99735b][u:f86d99735b]250mA Power Amplifier Kit[/u:f86d99735b][/color:f86d99735b][/size:f86d99735b][/url]
[img:f86d99735b]http://store.qkits.com/images/qk171.jpg[/img:f86d99735b]
“The circuit is specifically designed to amplify the output of 7mW to 10mW WBFM transmitters (wide band) to a final level of 250mW to 300mW”
It sells for around $20.00
Might be an easier solution to implement. Also, to give an idea of mW vs range, when I tested the [url=http://part15.us/modules.php?name=Reviews&rop=showcontent&id=2][b:f86d99735b]Compact Synthesized PLL FM STEREO Transmitter -10mW[/b:f86d99735b][/url] I used a simple dipole high and in the clear, and as I said in the review, “I was getting a car radio range of about 3000 feet north-south, and 2000 feet east-west. Portable radios couldn’t pick me out of the cross talk on the band as well, and I got about half that on the portables.”, so 250 mW into a good antenna just might do the trick.
As always, let us know how it turns out 😀
[quote:f86d99735b]By the way, RadioheadC, thanks. I thought that Part 15 FM used to have a 100mW/1meter standard. Apparently I’m not the only one.[/quote:f86d99735b]
[color=red:f86d99735b][b:f86d99735b]Me too![/b:f86d99735b][/color:f86d99735b]
Total posts : 45366Thanks guys.
FIRST off this is a really great website and forum. Thanks for all the devotion and hard work that goes into it.
SECOND
The antenna solution makes a lot of sense, although my family might have some objection to the aesthetics of a 5/8 or Flying Vee prominently “displayed outside.” Also I know that it would be some time before I could get around to that type of project. I had considered a 5/8 and “hiding” it in the attic (house is wood frame), but the combination of relatively low rafters, maybe too low for the 5/8, and how to get a feed up there is deterring me right now. Also the cost for those Comets or whatever… But I may look into this some more down the road…
FYI on the property shape, consider an irregular rectangle approx. 1200++ feet (road frontage) by 1600++ feet deep. (It is a bit irregular and a little bigger in parts.) The house sits in a corner, not too far from the road (150 – 200 feet). Road traffic is non-existant. The property slopes down to a small “hollow” or valley and the house is at high end of the property. The hill we are on (which probably climbs another 200-300 feet of elevation above and behind our house) would block propagation across the “near border.” Elevation drop to the bottom of our property is probably about another 200 feet. Area is very rural and I doubt that the few “neighbors” we have could pick up anything or would even care. A couple hills would effectively block propagation into the small town center, a few miles away. If I ever did want to experiment with community radio, I would have to find another site… (And maybe start another thread on directional wifi or something to get a studio signal there…, but first things first.)
The other issue as PhilB put it would be impedance match, and while I understand the concept, I am clueless as to its implementation with the C Crane FMT.
Right now I am just running the C Crane perched on the top of a high bookshelf in my office with a single (small guage) copper wire of one wavelength clipped to the built in whip antenna and hanging vertically. While it seems to work for now, obviously that has to change and any thoughts would be welcomed. Incidentally I did apply that hack to the C Crane FMT that I found elsewhere in the forum to tweak up its power. (My Belkin Tunecast II is lying mostly unused, except for occasional trips.) Audio is fed from the sound card of one of my office PCs using Windows Media Player. (Another thing that I will have to change over time, seeing all the cool PC audio tricks you guys seem to have.)
THIRD
Scwis, where do you find that kit that you have the picture for?(And how would I modify the C Crane for impedances?)
FINALLY, Ancient History
My past life Part 15 experiences were in the 1970’s. I dropped out of this hobby for a long time, so I do not know when the FM regs were changed from 100 mw, which a manufacturer could specify, to the incomprehensible numbers that we all don’t have meters to measure. Back in the 70’s, Radio Shack sold some “wireless mike” devices that used the FM broadcast band and had 100mw specs. I remember an RS kit that one of my friends built and we used for a couple of years for broadcasting and also a handheld mike (pre-assembled, whose case was about the size of, but not the shape of an E-V 635) that had an RCA jack for an aux audio input with a switch to override the built in mic. All was mono in those days (even for some commerical stations) and PLL was not in the picture for these devices, but then again none of the receivers were digital either, so it all sounded fine.
Total posts : 45366[quote:2ad0363170]THIRD
Scwis, where do you find that kit that you have the picture for?
[/quote:2ad0363170]
Uh, err, ummm, I guess I got too tricky for my own good – the post title was the link… Shouldn’t have put it in red, I guess… I fixed that, and here it is again[url=http://store.qkits.com/moreinfo.cfm/qk171][u:2ad0363170][size=12:2ad0363170]http://store.qkits.com/moreinfo.cfm/qk171[/size:2ad0363170][/u:2ad0363170][/url]
Gosh I feel dumb 😥
Sorry about that[quote:2ad0363170](And how would I modify the C Crane for impedances?) [/quote:2ad0363170]
I believe that amp will be OK for the C Crane output as-is 8)
Total posts : 45366Thanks for the link SCWIS. That looks like it’s worth an experiment. And the price ain’t too bad either! I would imagine from your post that the C Crane’s output is in the 7 – 10 mw range, or does anyone happen to know?
BTW, have you (or anyone you know) tried that particular kit?
Total posts : 45366Well, since you asked how it turns out …
First off, with time being at the greatest problem for me these days, I did a quick and dirty fix which I realize is far from ideal. I will work on a better one later. I did use the Radio Shack TV RF Amp with some success. I opened up the Crane FM T and soldered a short length of RG-58 C/U to where the whip antenna is soldered to the circuit board and grounded the shielding. (I had already “hacked” the Crane by adjusting the variable resistor, as posted elsewhere on the internet and referenced on these boards.) The coax feeds the TV amp, which goes into a balun. Admittedly the balun is not perfect since it is a 75 ohm (instead of 50 ohm) to 300 ohm balun. That then feeds an FM dipole (300 ohm wire) which is hung vertically with masking tape to the gypsum board wall.
The transmitter is fed by the sound card of my PC which is currently playing playlists of mp3’s that I ripped at 320k from my CD collection. I am using Windows Media Player 10 on an XP PC. I am just using this to play my music around the house and yard for the present. Not yet ready for community radio. We are in a very rural area, and few (if any) people could pick up the signal.
Range had good improvement and I can get a clear signal in most spots (there are a couple of blanked spots within the house). The signal reaches about 200 feet in one direction and 500+ in another, probably due to the terrain. (It’s hilly and we are on over 20++ acres). I could pick up a very scratchy signal on a very good car radio about a mile away, across the valley, but lost the signal in between where the road was below our house (probably due to shadowing from the hillside).
Audio quality is great, and when the music id on when we have company, the guests don’t realize the broadcast comes from my PC.
In retrospect, I really don’t have a clue about the power output of the Crane, which I originally thought was about 7 – 10 mw. I would guess it is below that.
I did order the QKit RF Amp, as well as another of their kits. I started with the other kit which I have not yet gotten to work (probably my poor workmanship) and haven’t had the time to fully diagnose it or start on the RF Amp. Another time maybe. Stay tuned…
Total posts : 45366A “Part 15” (not really) FM system radiating 25 mW from a 1/2-wave dipole can produce a field strength of ~420 uV/m over a reflection-free, line-of-sight path to a point 1/2 mile away, if that power is radiated in that direction. This is plenty of field for almost any FM receiver, and more field than a legal Part 15 FM system should produce only 9.84 feet (3 meters) from its antenna.
OTOH, a truly legal Part 15 FM system would produce about 9 uV/m for those conditions, at a distance of 1/2 mile. But that still is a useful signal for a decent FM receiver.
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