Canadian TV, Computing and Home Theatre Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
116 Posts
Discussion Starter #1
I have a silly question, can the CM4228HD receive FM stations? I just had this thought of running coax to my tuner, but I can't find any information if it'll work or not. I'll eventually have it split 3 ways in my living room, connected to the TV, MythTV box, and tuner.

I still have to figure out a way to stabilize the mast first.
 

·
Registered
Joined
·
116 Posts
Discussion Starter #3
Well, that's promising. It'd be nice to get something besides christian radio, which is terrible.
 

·
Super Moderator
Joined
·
5,074 Posts
It would work better with a VHF/FM antenna. But there's no reason why you couldn't pick up somewhat-local radio with a UHF antenna.

If you have a pre-amp with an FM trap, ensure that you turn this feature off. And set the input to "combined" if you have separate VHF/FM and UHF inputs.
 

·
OTA Forum Moderator
Joined
·
24,867 Posts
All I can add to that is that a CM4228HD will get better FM Radio reception than no antenna at all. ;)

Please read Post #19 in the OTA FAQ to see how far apart the FM Radio and UHF TV frequencies are on the RF spectrum.
 

·
Registered
Joined
·
116 Posts
Discussion Starter #6
Lol... I have aluminum siding, the stupid little piece of wire that came with the tuner does nothing... :D
 

·
Registered
Joined
·
92 Posts
FM is between channels 6-7 VHF and the CM4228 isn't good at low VHF. I hooked mine up to my receiver and stations below 100MHz were very weak.
 

·
Registered
Joined
·
7,131 Posts
Yes and no. Yes, it will work for local stations and other strong area stations. No, it won't work well for weak or distant stations. The main improvement will be due to getting the antenna above the aluminum siding and household interference.
 

·
Registered
Joined
·
1,980 Posts
HLSJ

I use a Hi-Lo splitter combiner to split off the Low VHF and FM. It works great. With my 4228's, I get FM from all Buffalo/Toronto/Hamiltion.
The Hi-Lo splitter causes no loss to the High VHF and UHF, so it doesn't hurt my ATSC tuners, and maybe it helps them since it stops the old Ch5 analog.
http://yhst-18278607509093.stores.yahoo.net/pico-0144.html
Works much better than a regular splitter.
 

·
Registered
Joined
·
79 Posts
I have a silly question, can the CM4228HD receive FM stations? I just had this thought of running coax to my tuner, but I can't find any information if it'll work or not. I'll eventually have it split 3 ways in my living room, connected to the TV, MythTV box, and tuner.
Technically even a simple meter long wire will pick up FM, although only the strongest signals. So almost any wired metal affair (coat hanger?) will pick up some FM, and I understand a UHF antenna will readily pick up FM, whereas a VHF will have less range. Your antenna is technically a UHF antenna.

For whatever reason distant FM is easier to receive than DTV as I know someone who has an old amplified FM table-top antenna (looks like a black plate) in the basement of his Oakville home and he receives FM from as far away as Buffalo.
 

·
Registered
Joined
·
6,257 Posts
One word of warning for those in an area that have a desired station on physical channel 6. Strong FM stations can make it difficult to receive a weak channel 6 so you might not want to combine VHF-LO and FM on the same cable. Some stations that plan to continue to use VHF-LO post transition include:
  • CHEK-DT (Victoria, BC)
  • CIII-DT (Paris, ON)
  • CIII-DT-6 (Ottawa, ON)
(This list may not be complete.)
 

·
Registered
Joined
·
1,980 Posts
One word of warning for those in an area that have a desired station on physical channel 6. Strong FM stations can make it difficult to receive a weak channel 6 so you might not want to combine VHF-LO and FM on the same cable. Some stations that plan to continue to use VHF-LO post transition include:
  • CHEK-DT (Victoria, BC)
  • CIII-DT (Paris, ON)
  • CIII-DT-6 (Ottawa, ON)
(This list may not be complete.)
will VHF-LO DTV still interfere with FM?
 

·
Banned
Joined
·
166 Posts
I had the same situation as you did today. I wanted a good FM antenna but I only have my 4228HD thats active. So I connected the coax from the antenna's preamp power inserter in to a distro amp and it does work. Well kind of. It's not the best but it works. I can get a Buffalo station on 96.1FM with the antenna and with out all I get is static but it sounds weird because you hear what is on 96.1 but you also hear whats on the Toronto station 96.3FM.
 

·
Registered
Joined
·
3,396 Posts
I ran 4nec2 sim on the OLD CM4228 (using Nist's CM4228a file) across the FM Band:
Horizontal Gain of 6-7 dBi towards REAR and 2 dBi toward FRONT but extremely excessive (1000:1) SWR,
so there are likely to be some frequencies that are nulled out....so try inserting different coax lengths.
Vertical Gain below 100 MHz was very low, but was 1-3 dB from 100 MHz to 108 MHz.

My 4nec2 sim model for the new CM4228HD is quite different across the FM Band:
Horizontal Gain to REAR, rising from -15 dBi to -4 dBi (not very useful) with excessive (200:1) SWR, but
Vertical Gain to FRONT, dropping from +4.2 dBi to -2 dBi (mediocre, but possibly useful).

But even a mediocre antenna on the ROOF is probably better than a Folded Dipole or Rabbit Ears INDOORS.
 

·
Registered
Joined
·
498 Posts
Technical question about having TV and FM purposes on the same antenna cable. My Buffalo FM stations are in line with the CN Tower. Which has more destructive influence on my Sony FM and FM-HD tuner reception, (a) strong stations because their frequencies are in spitting range of the FM frequencies or (b) strong stations because they overload the initial tuner amplification stages, regardless of their exact frequencies?

Thanks.
Ben
 

·
OTA Forum Moderator
Joined
·
24,867 Posts
bentoronto said:
having TV and FM purposes on the same antenna cable
The biggest problem with carrying both FM and TV on the same coax is the potential for harmonics from the FM stations messing with VHF-HI TV channels (7-13). For example, in Post #19 of the OTA FAQ there is a table of FM Radio frequencies in which I've included the harmonic frequency that would get hit, which you can cross reference with the VHF-HI table to see which station it would be.

As for your FM radio reception, no matter how good your FM tuner may be (and your Sony XDR-F1HD is the best!) if there are adjacent FM stations on the dial, such as a distant station on 105.5 being mangled by a less distant station on 105.3 and very local station on 105.7, there are all sorts of problems with intermodulation distortion, etc. etc. (as we discuss over in the Radio Forum).
 

·
Registered
Joined
·
3,396 Posts
Since most TV Tuners have a tunable RF Filter on their input that is about 3-5 channels wide,
strong signals in the FM Band will be attenuated, hence it is less likely to be causing problems:
http://www.tvtechnology.com/article/16356
Note that the shape of Figure 1 mimics the (inverse) shape of the input filter's frequency response.
Also note that strong adjacent signals desensitize the tuner by reducing the AutoGainControl.

BTW: Notice that I said "most" TV Tuners (e.g. Superheterodyne types). I have yet to see any
REAL test data re Double Conversion DTV Tuners, such as the Microtune RF Chip found in some
TiVo's, Echostar DVRs & Hauppauge USB Sticks, which apparently do NOT have an input filter:
http://www.odyseus.nildram.co.uk/Systems_And_Devices_Files/SuperHet.pdf
http://rfdesign.com/images/archive/0601Norsworthy67.pdf
http://www.wikinvest.com/stock/Microtune_(TUNE)/Customers

However, running TV and FM signals through the same Preamp and Distribution Amplifier
CAN be and probably WILL be a problem, not only due to generating 2nd Harmonics of FM signals
that fall within the Hi-VHF Band, but potentially by 3rd Harmonic Intermodulation Distortion
(IMD) that can fall on top of Ch4-6. If you check www.fmfool.com, you'll probably find that there
are several very strong FM transmitters near you, since many are distributed vice centralized:
http://tvtechnology.com/article/94868
http://www.tvtechnology.com/article/88282

Charles Rhodes [TVTechnology] article also describes how FM 2nd Harmonics within and close to
the Hi-VHF Band are part of the 3rd Harmonic IMD problem, mixing with other Hi-VHF signals:
http://tvtechnology.com/article/82716
http://www.tvtechnology.com/article/93086

I updated my "DTV Interference Calculator - Rev F" with an example (EX5) of FM
2nd Harmonic IMD on top of Ch6 as well as an example (EX6) of FM 2nd Harmonic IMD,
which could be mixing with other strong Hi-VHF signals (also note UHF 3rd Order IMD):
http://imageevent.com/holl_ands/files/ota
Users can download the Excel Spread Sheet and enter their own set of TV & FM frequencies.
 

·
Registered
Joined
·
3,396 Posts
Back to your original question....since even merely "good" FM Receivers provide good (60+ dB) to excellent
(90+ dB) alternate channel selectivity, the primary susceptibility to interference is an ADJACENT channel,
for which there is a trade-off (& maybe a switch), since TOO much filtering will increase audible distortion.
NEXT adjacent and all other FM Band & other signals aren't a problem, so they don't even bother testing
what DTV would call the "Taboo" channels.

Fol. website identifies how many "gangs" of variable capacitors are used in various (old) FM Receivers:
http://www.fmtunerinfo.com
One "gang" is used to tune the local oscillator, with 2-4 additional "gangs" used to tune
multiple narrow-band RF filters (prior to the mixer stage). This blocks nearly all undesired signals.
PS: Older, manually tuned capacitors have much higher "Q" than modern varactor diodes, so
more stages might be needed on modern designs to equal and frequently exceed the old designs.

Alas, my Kenwood KT7001 (4 "gangs", 3 FETs, Crystal IF Filters, 90 dB AltChSel, 1971 bought in Japan)
bit the dust a few years ago...after limping along on an external DC power supply for about 10-years.
Personally, I gave up listening to FM prior to its last gasp....SACDs & DVD-Audio spoiled me forever....

Due to copyright laws, it's difficult to find FM Tuner schematics on-line, although you can order them.
Here's a block diagram for the Pioneer KT-9800 I ran across, showing a 5 "gang" tuner:
http://www.fmtunerinfo.com/TX-9800block.pdf
FYI: "Double Filter" consists of two "Single Filter" stages, back-to-back without amplification.
 
1 - 19 of 19 Posts
Top