CM 4251 Feed adaptation

[Yeyo 2]

Hi i would like to know how to make a 7" CM4251 feed adaptation into 0.98m parabolic antenna. If someone can help me I appreciate a lot. Thanks

[Admin 2545]

,,,welcome Yeyo,,, something like that ... ???

,,, here you find something like that...

 

[Admin 2545]

,,, this type of antenna would be interesting to convert from UHF to HDTV (smaller antenna)...!!!

[clanon 246]

more info

[Yeyo 2]

Yes let me explain and I apologize for my english I speak spanish as my mother language. So the problema is that I have a 98cm home made parabolic antenna and I need to make an adaptation of the CM4251 feed that fit to my 98cm parabolic antenna and I don't known how to do it. If exist another antenna type (I mean feed antenna) much better in gain etc than the CM4251 one would be better to use with mine please let me know the measure please. Thank you friend. 

[clanon 246]

The original FEED is for a 6' 7' 1,8mts 2.1 mts diameter GRILL

Parabolic Antenna F/d ratio is important (te indica el tipo de iluminación necesaria par eficiencia mayor a: digamos 70 % , que es lo que se busca como objetivo)

Having the original feed wouldn't be better to copy the original GRILL

Edited January 14, 2022 by clanon

[Harry36 140]

1 hour ago, Yeyo said:

Yes let me explain and I apologize for my english I speak spanish as my mother language. So the problema is that I have a 98cm home made parabolic antenna and I need to make an adaptation of the CM4251 feed that fit to my 98cm parabolic antenna and I don't known how to do it. If exist another antenna type (I mean feed antenna) much better in gain etc than the CM4251 one would be better to use with mine please let me know the measure please. Thank you friend. 

For the TV range 470-790 MHz, the mirror diameter of 0,98 meter is small. You won't get good gain from such an antenna. The maximum theoretical gain at 470 MHz for a dish diameter of 98 cm is 10.6 dBi. for a frequency of 790 MHz - 15.2 dBi. You will get exactly the same parameters using the Uda-Yaga antenna, about 1.2 meters long and about 30 cm wide.

https://ypylypenko.livejournal.com/91602.html

For manufacturing, you will need an aluminum strip with a section of 15x2 mm, a profile pipe with a section of 15x15 mm, rivets or self-tapping screws, metal cutters and about 1 ... 2 hours of free time. It would be very good to purchase a matching board and a box for it. But if this is not the case, a loop of impedance matching cable will do.The CM4251 antenna is very good and beautiful, it does not need to be dismantled or destroyed. Sell it to antique lovers.

[Yeyo 2]

13 hours ago, Admin said:

,,, this type of antenna would be interesting to convert from UHF to HDTV (smaller antenna)...!!!

I'm sorry, friends, I didn't know how to explain myself well. I really don't have the CM4251, I wish I had it. I have a 98cm parabolic not dish type made at home and what I need is an antenna to feed it that its working range will serve me for the HD television channels that the USA transmits, which would be the ATSC standard,antenna should be the best possible because I live in Cuba and the distance is 90 miles, although I don't know if the gain should come from the antenna itself or from the parabola. I hope I have explained myself better and many thanks to the friends who help me with their comments. Greetings from Cuba.

[Harry36 140]

5 hours ago, clanon said:

,,,

batwing? 350*350 mm reflector?

[Yeyo 2]

18 hours ago, Admin said:

,,, this type of antenna would be interesting to convert from UHF to HDTV (smaller antenna)...!!!

How can I do that?? can you show me please

18 hours ago, Admin said:

,,, this type of antenna would be interesting to convert from UHF to HDTV (smaller antenna)...!!!

 

3 hours ago, Harry36 said:

batwing? 350*350 mm reflector?

 

[Yeyo 2]

Hello everybody I wonder if rescaling an LPDA 9EL antenna for the new American HDTV can be used to feed my 0.98cm parabolic antenna.

[yurik82 9]

On 14.01.2022 at 8:04 PM, Harry36 said:

The maximum theoretical gain at 470 MHz for a dish diameter of 98 cm is 10.6 dBi. for a frequency of 790 MHz - 15.2 dBi

upper fundamental limit is 13.7/17.1 dBi for 470/700 MHz

to get any gain from dish - one need dish feeder (illuminator).

Feeder itself typically have gain in range 9...14 dBi (optimal directivity depsnds on f/D of parabolic dish)

If you have feeder with 10...14 dBi gain, why would you add extra parabolic dish to get the same 10...14 dBi (at 50% illumination efficiecny, which is very good efficiency, hard to achieve)?

Bad news is that you can't achieve 50% illimination efficiency at UHF. For offset parabolic dish 30% I consider very good result, and for center-fed dish 20% is very good, due to shadowing.

 

[clanon 246]

2,1 mts diameter , i assume