Best Antenna for Modulus 3000

[Jeff Cook]

I have a Modulus 3000 and I am looking to add a better antenna on the TV receiver side of the setup.

 

I know there are a thousand different reasons for signal interference, (location, other equipment, movement, etc.), and I know TV receivers vary, but is there an antenna that seems to work best?

 

Thanks,

 

Jeff Cook

[Robert Starling SOC]

Hey Jeff!

 

Contact Amateur Electronic Supply and ask for a dual band VHF / UHF telescopic antenna and also get a "rubber ducky" version. Also, the back of the TU1041U has an F connector for the antenna so go to Radio Shack or ask the guys at AES for a right angle F connector male to BNC that the antenna will connect to.

[Jess Haas SOC]

Those antennas may work fine but I have a feeling that they aren't going to be the best antennas possible for a couple of reasons. For one Amateur radio antennas are tuned for amateur radio frequencies which are a bit lower than TV frequencies. Also they are 50ohm antennas while the F jack on the back of your receiver is 75ohm which is going to lead to a bit of signal loss.

 

~Jess

[Robert Starling SOC]

Those antennas may work fine but I have a feeling that they aren't going to be the best antennas possible for a couple of reasons....

 

Hey Jess,

 

Technically yes you are absolutely 100% correct. Practically speaking though the impedance is less of an issue with reception than transmit. Going by the book any antenna not designed and cut to the exact frequency is a compromise. The frequency range we're transmitting in is so broad from the low end to top end that I calculated at one point that it would take five to six custom cut antennas to reduce VSWR to an acceptable level for transmit across the frequencies covered by a Modulus or CanaTrans... but we all use a single little rubber duck for transmit pretty much without a clue as to what freq it is cut for. The transmit loss from a poorly tuned transmit antenna is much much more of an issue than the receive antenna impedance unless you're pulling a long run of lossy coax on the receive end. At least CanaTrans made an effort to provide two transmit antennas. I don't know if Modulus / CIT ever did that?

 

The receive issues we all deal with are mostly multiplexing / deflection, blocking and interference. Diversity receivers with a combination of directional / gain antennas and omni-directional antennas are about the best we can do in our world. Then we get into signal processing within the receiver once the antenna has "caught" the signal; we're not running coax in the instance above and the signal processing of the Sony is as good as you can get for single antenna technology; much better than a store bought consumer television.

 

I've been building directional and omni-direction antenna arrays for amateur radio competitions for about 25 years, some measured in centimeters and some more than 1600 feet; we've built VHF and UHF antennas designed to bounce RF off the charged particles of meteor scatter as they hit the atmosphere and "antenna farms" designed to receive a .25 mw signal from the other side of the earth. By the same token, I'm also old enough to have seen way too many "rabbit ears" or coat hangers wrapped in aluminum foil that improved the reception on television sets.. whatever the impedance was didn't matter; it "caught" the signal.

 

For simplicity a rubber duck, telescopic omni or even a coat hanger with some aluminum foil as a receive antenna on that Sony would probably be all about the same. Jeff can step it up with a directional yagi / shark fin but then that is very directional when used on it's vertical axis and even then it is not completely broadbanded enough for acceptable transmit. For a better solution and wider field of coverage simply turn the shark fin / yagi on it's side the same as you see regular exterior antennas, amateur radio and military yagis.

 

At one point I investigated some of the small TV antennas at Best Buy and Radio Shack that have built-in preamps. They seemed like an affordable option at $70 +/- but it was just one more thing to pack, carry and power.

 

Now... if I could just find my old iambic paddle Morse code key....

 

Peace!

[Charles Papert]

Wow Robert, great response!

 

I don't know if Modulus / CIT ever did that?

 

Years ago I bought a "high gain" transmit antennae from CIT, it's about 14" long and labelled "ch. 35-55" (this from memory, don't feel like going down to the cases to confirm this).

 

On a slightly related subject, does it drive anyone else crazy that 90% of the time, when the video assist guy or the camera assistants are in charge of picking channels they will just randomly announce one without checking first to see if there is an existing signal on that channel? Am I crazy in thinking it helps to find a channel that is pure static, hopefully with nothing on the channels on either side?

 

That said, due to the way that the Modulus synthesizes its range, are there certain channels that are inherently more "punchy" on the unit than others?

[Alfeo Dixon SOC]

I don't know if Modulus / CIT ever did that?

 

Years ago I bought a "high gain" transmit antennae from CIT, it's about 14" long and labelled "ch. 35-55" (this from memory, don't feel like going down to the cases to confirm this).

 

Yep, but its about a foot and a half for channels 30-50

 

"rabbit ears" or coat hangers wrapped in aluminum foil that improved the reception on television sets..

 

Hmmm... I wonder how the director would respond the next time he/she yelled out "can you fix this and make it better.." and I pulled out the aluminum foil and wrapped his antenna?!? yet another reason to hang out at crafty!

 

-Alfeo

[Jess Haas SOC]

Technically yes you are absolutely 100% correct. Practically speaking though the impedance is less of an issue with reception than transmit. Going by the book any antenna not designed and cut to the exact frequency is a compromise.

I said that they should work fine, but they are definitely not ideal or the best antenna possible.

 

The frequency range we're transmitting in is so broad from the low end to top end that I calculated at one point that it would take five to six custom cut antennas to reduce VSWR to an acceptable level for transmit across the frequencies covered by a Modulus or CanaTrans... but we all use a single little rubber duck for transmit pretty much without a clue as to what freq it is cut for.

I bet this is contributing to how damn hot the modulus gets....

Maybe I will get around to cutting some 1/4wave UHF whips for mine one of these days. They wouldn't be very long and should perform better.

 

The transmit loss from a poorly tuned transmit antenna is much much more of an issue than the receive antenna impedance

I completely agree, but just because one part is not ideal does not mean that improving another will not improve performance. Got any suggestions for correctly tuned transmit antennas?

 

 

For a better solution and wider field of coverage simply turn the shark fin / yagi on it's side the same as you see regular exterior antennas, amateur radio and military yagis.

Won't this result in a horizontally polarized antenna while your transmit antenna is vertically polarized? Won't this result in significant signal loss? You could of course horizontally polarize your transmit antenna but then you will have weak spots off the sides...

 

For the record I have a sharkfin but will sometimes use a horribly misstuned 50ohm whip antenna on my receiver.

 

~Jess

Edited September 26, 2008 by Jess Haas

[Robert Starling SOC]

That said, due to the way that the Modulus synthesizes its range, are there certain channels that are inherently more "punchy" on the unit than others?

 

Hey Charles!

 

I can't answer for the specific design of the Modulus but transmit circuitry has to be "tuned" for optimum performance the same as any other link in the transmit chain. Some sophisticated multi-band transmitters have optimized RF output sections but I don't know exactly how they accomplish it other than to use an internal antenna tuner circuit that always presents a 50 or 75 ohm load to the transmit amplifier. They probably have to do that to avoid burning out the RF amp; at least you would hope so.

 

I'd likely guess as well that the transmit circuitry and antennas are 50 ohms, not 75 as we would think of it once the signal is converted back to video. That is a good question for Emery Soos.

 

You could use a Bird digital watt meter with a dummy load to test the exact output at the antenna BNC to determine at what frequency you get the most power out before the signal reaches the antenna. Again though, practically speaking it is probably negligible but then again it may not be; mid-range you may get 1 watt, but toward the outer limits on each end you may get less, even half that; someone like Terry West might have an answer to this or Wolf Seeburg. CanaTrans appears to try to address this issue with the two antennas.

[Robert Starling SOC]

Got any suggestions for correctly tuned transmit antennas?

 

I found a company online about a year or so ago, placed an order for five specifically cut antennas and they never delivered. Basically they did not have the range of dummy load slugs or transmitters to test the freqs we use.

 

You could always "roll your own" !

[Robert Starling SOC]

Won't this result in a horizontally polarized antenna while your transmit antenna is vertically polarized? Won't this result in significant signal loss? You could of course horizontally polarize your transmit antenna but then you will have weak spots off the sides...

 

My omni-directional transmit antennas on the CanaTrans have right angle swivels. Even if your antenna does not have a swivel I heard that velcro sticks in both directions so just turn the transmitter if polarization concerns you. ;-} Again, going back to practical applications in our world, once you're in a studio or closed space, the signal is bouncing all over from every direction which is what is causing the multiplexing / deflection and blocking. Outside in a pure line-of-sight signal with a high-gain, highly directional yagi, yes you'd be better off orienting the antennas in a complimentary position whether vertical or horizontal.

[Jess Haas SOC]

I can easily transmit with a horizontal antenna but then it is not transmitting very well off the ends of the antenna which could lead to a weak signal when oriented accordingly. While the bouncing around inside will lead to a significant amount of signal with an altered polarization I would think that polarizing your antenna for this would result in more problems with multipath, etc... I have played a little with my shark fin being horizontal and it seemed to work better when vertical although my tests were not very scientific and may have been specific to the location. If something works for you I recommend using it as what works in practice is far more important than what works in theory. That being said a little idea of the theory can lead to better results in practice.

 

~Jess

[William Coss]

Check out this web site for broad band UHF antennas. Also just because a channel appears to be unused there now exists the possibility, a good possibility, of a DTV station being there which you would not see but will interfere with your low power analog signal.

 

 

 

http://www.wa5vjb.com/products1.htm

 

Bill

[Jeff Cook]

Ok, I think I need to get an antenna for my brain to take in all this technical info?

 

So what you are saying is that there is no standard with it comes to antennas. Omni, whip, blade, aluminum foil, whatever works. Is that what I am hearing?

 

I was kind of hoping of a part number and a contact, but whatever.

[Robert Starling SOC]

Hey Jeff, you can get a shark fin or an omni dual band whip covering the television frequencies. You can just as easily go to Radio Shack or Best Buy and purchase a set of modern "rabbit ears" which are now designed without the two telescopic antennas usually; a bit more modern. If you go with dual lead connections (the old style flat wire for TV antennas), you'll need a twin lead to F connector. I got one from David Hable at Cramped attic but you may be able to get one from Radio Shack or BTX. Just as easily you can call AES get a dual band VHF / UHF rubber duck and/or telescopic, and F to BNC connector and be okay too. These things are very inexpensive probably from $5 to $50 max.

 

I have a little whip I got from Bill Coss and a CIT Sharkfin. Both worked excellent with the TU1041U and now I use them both with the DX400 diversity receiver. The shark fins are nice. If you want one of the original CIT Sharkfins, Derrick Whitehouse still has a few in stock.

 

It's just a receiver so don't be afraid to try something of your own if you want; any piece of metal or wire can be and already is an antenna.

 

The direct answer to your BEST receive antenna question is an antenna that has been specifically cut and designed for the exact frequency you are transmitting on. Since your Modulus transmits on so many channel that are so far apart something made for the middle range would be most acceptable which is what most of us are using.... something acceptable.

[William Coss]

Let me repost this a little different.

 

http://www.wa5vjb.com/

 

Bill