Canadian TV, Computing and Home Theatre Forums banner
1 - 3 of 3 Posts

·
Registered
Joined
·
3 Posts
Hello all - 16 bay clone of CM4228

Hi all,

A quick note of introduction. I've been browsing the web for a few months looking for information on how to improve my reception of Boston tv station in Ayer, MA (25-30 mi). Coming across you all is a blessing, and I've reviewed most, if not all of your thread on "Channel Master Model 4228 Antennas."

I ended up building a clone of sorts of two CM 4228 ganged (still trying to connect wires appropriately). The difference between my antenna and the real thing is that mine is made of 8 gauge copper bowties 7" V legs spaced roughly 7" apart, galvanized steel 1/2" gridded reflector, twin lead, and the rest are plastic and duct tape. It is an indoor antenna of about 10 lbs. and receives most Boston stations (GBH, GBX, ABC, NBC, CBS, CW, but not Fox, LVI, and Ion) at 90% or greater strength. The SAD thing is that my cloned 8 bay works just as well and built the exact same way. I've TRIED to gang the pair of 8's parrellel/series as well as parrellel with shared CM 7777 pre-amp, but not with splitter and dual pre-amps. But results aren't any better than 8 bay. I'll keep trying but would LOVE SOME HELP. Can't want to see results from the fella experimenting with connections for ganging 4228's. Thanks for your time.

I also have two questions on my mind:

1) Why aren't directors ever used on CM bowtie antennas?

2) How can I get better results than an 8 bay, fudge?!?
 

·
Registered
Joined
·
3 Posts
Stampeder,

Thanks for the comments. I've checked out the DBGH superantenna. It's an interesting read, and I'm sure that I'll keep updated.

fbov,

Your analysis of the dimensions on my attempt at a 16 bay clone is very valuable. What program(s) did you use, or did you do it all long hand? I'm a designer by training so I would much rather "model" things out before hacking away like I have. Do you or anyone else have recommendations for programs/books with noncalculus formulars for calculating shapes of radiating elements, spacing, and the likes?

I've checked out the hdtvprimer instructions earlier, and have already tried both their suggested serial/parrellel with 4:1 balum and the parrellel only gains for my four 4 bays. I did not see improvements of the 16 bays (8 bays vertically stack) to just one 8 bay (4 bays side-side). In fact, I had better reception when I built an 8 bay all out of twin lead. And yes, I included the twists at the top and bottom of each 4 bays for "phasing" reasons, but I'd like to know more about calculating phasing.

Tvfools is great. I'm inserting their reading of my specific location for your review -- the name of my area is Nasoba VALLEY. Love to hear additional comments from you about my stuff and about your own successes. Thanks again for your time.

 

·
Registered
Joined
·
3 Posts
CM bowties and digression to Archimedian Spiral

Frank,

Thanks for your explanations of antenna dimensions, phasing, scaling, and pre amp overload. Now I know to check my dimensions and scale it to the right frequency. Also you may be right about pre amp overload. Channel UNI is quite strong and my Channel Master 7777 gives an additional 28 db boost. I'll have to adjust my reflector or shorten the side lobes somehow to get rid of that station completely. The only thing I watch on it is soccer anyway. Gooooooaaaaaal!

You seem like someone with whom I can have a good discussion about an antenna design that I found in a book called Modern Antenna Design by Thomas Milligan. Under the Self-Scaling Antennas chapter, the Archimedian Spiral Antenna appears as a quasi-self-scaling piece. It radiates over a large frequency band! One can designate the lowest frequency by making the distance of the spiral's circular perimeter 1.25 times the wavelength. In other words, the circumference of the antenna is 1.25 times the lowest frequency's wavelength. From the outer edge and opposite of each other in position, two elements spiral inwards leaving only their width as the spacing between the already turned outer spiral and themselves. The turning must progress to at least 0.25 wavelength and continue to as high a frequency as space allows. My guestimate suggests that the spiral will have less than a half meter diameter when set for UHF levels. Can you or anyone "model" it for it's properties such as gain, possibilities of using a reflector, and making an array perhaps? Awaiting anyone's response. Thanks.

Lee
 
1 - 3 of 3 Posts
Top