The CM4228 (original), as is, can very capably receive VHF-HI signals in a metro-to-near fringe location precisely due to the combned width of its reflectors. This has been known for many years, so essentially the 2 screens act as one. On my own CM4228 they touch.

Just curious if I was stack two of the antennas (as below), should I just butt up the black plastic end caps together then tie with non-metallic clamps of some sort? (I'm still a bit confused because in the case of the 4221's,the metal reflectors are touching when stacked...right?
Thanks
http://i14.photobucket.com/albums/a321/wee-haggis/ANT20852.jpg

The best way to look at the problem is to think of the antenna in the picture as an entire, whole unit. The idea of stacking is to gang two whole units, one on top of the other. In your case, put them on a pole facing the same direction and slide the bottom one up until it touches the top one, where ever that may be on the antennas. Connect the outputs as recommended and bob's your uncle. :)

If you are enterprising you could tighten the top one solidly but put the lower one up with wingnuts or other easy fasteners so that you could experiment with different gaps to see if reception is aided in any way.

Ok...thanks Stampeder I'll give it a try.

You could hack-saw about an inch off the top and bottom of the vertical bowtie mount bar in case you want to try having them up closer to eachother. Don't do it unless you can afford to kiss the antennas good bye if the cut ruins them! :D

In a "perfect", loss-less combiner, signals in-phase would yield 3 dB gain and
out-of-phase would CANCEL. With unequal signal amplitudes, the output signal
would be a (complex) addition of the inputs.

Stripline (aka Wilkinson) Couplers are very close to this ideal (typ 0.2 to 0.5 dB loss).
The Lindsay UHF Stripline Coupler cost about $100, back when you could still get it...
Various other companies make VHF and UHF Stripline Couplers, but I have yet
to located something "affordable" for the entire UHF band.

However, a cheap RF Spitter/Combiner is more complicated, since it contains
a Hybid Transformer and Mismatch Resistor:
http://www.macom.com/Application%20Notes/pdf/m560.pdf
http://www.macom.com/Application%20Notes/pdf/m561.pdf
http://www.macom.com/Application%20Notes/pdf/m568.pdf

Any phase or amplitude differences between inputs will be lost in the
internal mismatch resistor. With a typical internal loss of 0.3 to 0.5, the
combining gain reaches a max of about 2.5-2.7 dB ONLY when the
two antennas are perfectly matched in GAIN AND PHASE...good luck...

However, stacking antennas ALSO provides the ability for one antenna to maintain
good signal strength while the other suffers a multipath null....which would be
even more effective if a Stripline coupler avoids the Hybrid mismatch loss.

If antennas are pointed in different directions, the loss is closer to 3.3-3.5+ dB
(I've measured up to 4 dB in some splitters).

I am in the process of figuring out how to stack 2 - 4 bay antennas (I haven;t decided whether I will stack them vertically or horizontally).
I have read different methods of checking to make sure the phasing is correct (since my 2 antennas are identical with the baluns built into them).
Would a simple way to do this be (using an ohmmeter), confirm that the aluminum left and right bows correspond to the other antennas ,equivalent bows by continuity testing?
thanks

I have read different methods of checking to make sure the phasing is correct (since my 2 antennas are identical with the baluns built into them).
Would a simple way to do this be (using an ohmmeter), confirm that the aluminum left and right bows correspond to the other antennas ,equivalent bows by continuity testing?


Nope, you cant check balun phasing with an ohmmeter. The simple way to check is to try it and note the reception, then reverse one, and check again.

300ohm.

I'm sorry to question your response (you obviously know a lot more about OTA antennas than I do),but my electrical theory makes me say .....mmmm to your response.
If phasing is another word for polarity,then you only have two choices (the conductor or the shield). If each of the conductor and shield wires goes to one bow or another (left and right) then by testing the continuity from the shield of the 75 ohm female jack and the continuity of the conductor side of the jack to the bow left or right,then my assumption would be that by sitting the 2 - 4 bay antennas side by side and confirming which bows go to which side of the 75 ohm jack would prove their polarity.
I do realize that all of the 4 and 8 bay bowties have crossover wires,but as long as the crossovers and bow positions match with each other,isn't that the same as confirming the phasing? I also realize that the ohmmeter would be reading through an impedance transformer and stepping up to 300 ohms,but couldn't this increased resistance be taken into account when testing the phasing ?
Or.... am I way off on a tangent ?.....If so,I apologize for ranting a load of BS :p;)

Unfortunately it doesn't seem to be that simple. Try checking out a commercial balun/transformer with an ohmmeter -- nothing stands out from any way of arranging the two probes.

Internally, they probably use double wire coils or something (like a power transformer), so nothing favours one side over the other when measuring it.

But yes, there is a polarity (or, rather, a phase) when connected to an antenna.

Cheers

I also realize that the ohmmeter would be reading through an impedance transformer and stepping up to 300 ohms,but couldn't this increased resistance be taken into account when testing the phasing ?
Or.... am I way off on a tangent ?.....If so,I apologize for ranting a load of BS

Ohmeters use direct current to measure resistance. DC generally doesn't pass through a balun, and even if it did, it would not tell you anything about phasing.

Also, you cant measure the imaginary impedance component part of the total impedance. (unless maybe you use your imagination, heh)

I currently have one OTA antenna & would like to get a 2nd identical one to use together.

I know they have to be identical & spaced far enough apart & aiming in the same direction with two equal lengths used.

I have been reading up on this and have just one question:

Can I just connect the outputs of both these antenna's into a splitter, then to my preamp then to the TV?

Any help would be greatly appreciated.

Thanks in Advance.

Can I just connect the outputs of both these antenna's into a splitter, then to my preamp then to the TV?Yes, that's the typical way to combine them into one preamp, or another is to buy a preamp with 2 inputs. You should be fine. :)

Thanks Stampeder.

Hello,

I am living in east GTA and having a hell of a time capturing everthing from Buffalo to CN Tower and beyond. Kind of like those people living in Hamilton. I was wondering if I could use two antennas, of the same type and point one to Toronto and one to Buffalo and then use a multiplexer to combine the signals. If that would work. I really do not want to install a rotor.

Has anyone tried this?

Thanks.

Please read through the OTA FAQ and especially Post #16 which is all about how to use 2 or more antennas together. ------------------------------------->

My quest to improve reception of WVNY-DT on VHF 13 continues...

Is-it better to put a balun on each antenna, then join them together by identical coax length to a 2-way splitter used in reverse or to connect their feed point with 300 ohm twin lead and use a single balun in the middle?

- Antenna 1: homemade Yagi, 10 elements for VHF 13.
- Antenna 2: 10y13s

I tested each antenna individually, each one gives about 42% signal on WVNY-DT

I connected them with the first method, putting them side by side, pointing to the same direction and spread about 2m apart, the signal seems to improve to 44% when combined. I also tried reversing the polarity on one of the balun but it did not change anything.

I also tried stacking them one above another, with about 1m apart (space limited in the attic), the combined signal is worse, even if I reverse one of the polarity.

So before I go out and buy twinlead wires, I would like to get some advice

thank you.

Have you read Post #16 in the OTA FAQ? Here's a small part of that post:And here's an experimental alternative to using a coax splitter when stacking identical antennas, but the problem is that the "rated" 300ohm impedence of each antenna (as broadband antennas their real world impedence is variable depending on the frequency of each channel) will combine to result in only 150ohms, which will cause a typical 4:1 balun to yield only 37.5ohm impedence on the coax downlead on some channels. This means that some channels may be weaker than the coax splitter technique while some may be stronger.

1. get about 8 to 10 feet of 300ohm twinlead (the old fashioned stuff)
2. connect both antennas with it, leaving about 2 inches of extra length
3. measure the length of that twinlead connection as exactly as possible
4. mark the exact middle of the length
5. cut and strip the 300ohm twinlead at that middle point
6. temporarily attach the balun to those twinlead ends (as the unison point of the output from both antennas)
7. connect your coax downlead to the balun
8. test by watching TV on a distant analogue station
9. if the reception is great your antennas are in phase and you can solder, twist, or crimp the twinlead ends to the balun and cover it with roofing tar or heavy duty electrical tape
10. if the antennas are out of phase your reception will be horrible
11. fix that by simply switching the two conductors on just one of the twin leads
12. test again, and it should be fine to permanently attach all the connectors

I went to buy some twinleads yesterday, they are harder to find than coax and more expensive too.

Here are the results:
- using twinleads, I connected both antennas feedpoint using two identical lengths and a balun in the middle that feeds the preamp. I tested on VHF12 analog, the image was very bad the first time. I then reversed the polarity on one of the antenna and the image was almost perfect.

- now with WVNY-DT: using twinleads, the signal seems much more unstable than the with the coax. The signal indicator on my TV shows large fluctuations from 30% to 60% constantly whereas with the coax method, the signal is pretty steady around 42-45%.

Does that mean the coax is catching noise, reflection etc.? I tried to move the twinleads away from objects (in the attic) but it did not help. By the way, the store where I bought twinleads had only the less expensive type available. Does it exist shielded twinleads and should I expect to see an improvement on the fluctuations? A steady reception around 50% will make me happy