FM antenna for VHF Hi?

[Schmerpy]

I live near 9th line and 407 and currently have a dB4e + CM7778 on my roof, which easily pulls in all Toronto stations + all Buffalo stations + CITS.

I'd like to use my setup for FM as well.

I have purchased a Magnum Dynalab ST-02 to use with my Yamaha T-2 FM tuner.

I'd expect that since my dB4e pulls in CTV 9 without any problems that the FM whip antenna would too.

My plan is to have the ST-02 mounted atop my mast, attach it to the VHF/FM input on the 7778, turn off the FM trap, and of course set the 7778 to separate inputs.

Has anyone tried putting FM on the DTV cable? Any problems observed?

Any comments?

[holl_ands]

You are only about 17-miles away from many strong, Line-Of-Sight, FM transmitters (enter your Lat/Long into www.fmfool.com). When they go through a Preamp, they WILL generate second harmonics on top of Ch7-13 and 3rd/5th/etc Intermodulation Distortion (IMD) on top of other FM Band stations and Ch4-6. IMD from strong VHF TV stations (as well as other bands) can also degrade FM reception. IMD will degrade sensitivity on weak stations but is unlikely to affect your many strong stations.

You should run a separate coax for your FM antenna to avoid this issue. Since Coax Loss is much less for FM Band frequencies, a Preamp under non-overloaded conditions doesn't provide very much of an improvement over the excellent sensitivity provided by most FM Tuners anyway....

If you are looking for a significant improvement in FM reception, consider a higher Gain FM Antenna, including Circularly Polarized antennas that can coherent sum together the Horizontal and Vertical FM signals for a 3 dB increase in LOS conditions and much more against Multipath. I analyzed a variety of Omni and Quasi-Omni Antennas here: [Vertical Whip was the WORSE.]
http://imageevent.com/holl_ands/omni
http://imageevent.com/holl_ands/circularpolarized

Just like many FM Transmitter "TURNSTILE" Antennas, it is possible to STACK multiple Omni Antennas, although I haven't (yet) worked out the "optimum" separations and feedline arrangements.

FYI: I discussed FM Tuner Specs vs FMFool calculated signals levels & FM Omni Antennas here:
http://www.digitalhome.ca/forum/show....php?p=1369091
http://www.digitalhome.ca/forum/show....php?p=1362877
http://www.digitalhome.ca/forum/show....php?p=1068465

You should also visit K6STI's extensive FM Antenna website:
http://ham-radio.com/k6sti

[DrSat]

Please note that the CM 7778 does NOT have a separate VHF input like the CM 7777 so it is best to run another coax and setup a dedicated antenna for FM reception. Turning off the FM trap on your CM 7778 will most likely impact reception of some of your weaker channels so it is not recommended. The DB4e was designed as a UHF only antenna so it would have poor FM reception anyways.


Best regards,

Dr. Sat

[Schmerpy]

Interesting. I installed a 7778 a couple of years ago that definitely did have separate VHF/UHF inputs. But my current 7778 is a newer one and I honestly don't remember what's up there now. It's really frustrating how these companies keep making everything cheaper and cheaper.

Can't say I really have any weak stations - they're either 85%+ on my CM7000PAL or I don't get them. Perhaps I'll need to try a VHF/UHF combiner before the AMP.

Running another cable would be a royal PITA.

We'll see how it goes.

[ExDilbert]

That's the problem with preamps, especially high gain models. They amplify *everything*, including noise. They also introduce their own noise plus overloading and spurious harmonics into the system. I've got channels with 85% signal where no channel exists because it's all noise. Add a preamp and it goes to 100%. Still no signal because there isn't one. What matters is signal quality and signal to noise (S/N) ratio. If the signal cannot be decoded, it doesn't matter how strong it is. I'd rather have a steady 60% signal with no multipath, no interference and high S/N ratio that a 100% signal that's 85% noise and garbage. The main problem with digital is that signal deterioration cannot be seen, the picture just disappears. With analog, it was possible to see how antenna misalignment or adding the wrong kind of equipment would affect the signal quality.

[roger1818]

Originally Posted by Schmerpy

I have purchased a Magnum Dynalab ST-02 to use with my Yamaha T-2 FM tuner.

The ST-02 is a whip antenna and thus only receives vertically polarized signals. Most TV broadcasts are horizontally polarized so it is unlikely that this antenna will receive them very well at all (FM broadcasts are typically circularly or elliptically polarized so they have both horizontal and vertical components).

If you did want to combine the signals, I would use a TV / FM Diplexer after the pre-amp. Just make sure it passes power on the TV side of the diplexer. It will likely block channels 5 and 6, but that isn't a problem for most people.

[Schmerpy]

Roger,

That would be ideal - I had no idea TV/FM diplexers existed!

They seem hard to find, though. Where to get them?

[roger1818]

Google the Winegard CA-8800. It has been discontinued, but you may be able to find one somewhere. Alternately there is the SOONTAI DPX1-TV/FM Diplexer, but I don't know where you can buy that or if it is even available in North America.

FYI, I don't have experience with either these so I am not sure about their suitability for your purpose.

[Schmerpy]

Thanks, Roger!

I called Save and Replay and they still had one, so it's on its way. This will make my life much easier.

It's still not clear to me whether this thing passes DC on the TV side. It says "AC passive", which doesn't have any meaning to me.

Either way, I'll make it work.

[HDTV101]

One of these Omni antennas will work great for FM radio in all directions.

[holl_ands]

Actually it's a Quasi-Omni, with Gain Max along one 45-deg diagonal and deep Nulls along the other 45-deg diagonal, so it doesn't provide good performance in ALL directions...Good Horizontal Polarization (only) Gain for perhaps only 1/2 of all directions. So you have to decide which direction you want the Nulls to be....after VERY CAREFULLY checking the harness connections to determine which way is a Null and which is a Beam (or trial and error). Several other Quasi-Omni and a (very) few True Omni FM Antennas are analyzed here:
http://imageevent.com/holl_ands/omni

FYI: I just added 4nec2 analysis of the Antennacraft FMSS Turnstile if it is ROTATED so that one of the Folded Dipoles is Vertical....providing many of the benefits of a Vertical Dipole plus a Horizontal Folded Dipole. This works well for both Vertically Polarized and Circular/Elliptical Polarized FM signals, with the usual Bi-Directional pattern for Horizontal Polarized signals. So it is somewhat like a normal FMSS, but with Beam Direction along X-Axis and Nulls to side rather than Beams and Nulls on opposite 45-deg diagonals:
http://imageevent.com/holl_ands/omni...eacfmssrotated

[ExDilbert]

A simple dipole will work as well or better than most commercial omnidirectional antennas. Anyone who wants good FM reception will get a 6 or 10 element yagi and rotor. If signals from only one direction are required, the rotor can be dispensed with.