Field Test of BSC621 series feeds by Satman Canada

 

 
 
 
 
 
 
 The DMS  BSC621(4DTV) and BSC 621/2 (FTA) are a great replacement product. Most C-band users have a polorizer that changes polarity by means of a small motor. In harsh climates such as Winnipeg these units fail after a few years of operation. It goes without saying that these units never fail  on a bright sunny day but usually at harsh temperatures well below 0

Here is the procedure for checking your Polorotor

 
  1. Have someone inside change channels on the satellite receiver. If you hear the servo motor turning, but there is no apparent change in the position of the probe (remove the throat cover and look inside the throat to see the probe), remove the servo motor and pull up gently on the amber colored drive shaft that couples to the servo motor. If the shaft pulls out, you will need to send the entire feed to Chaparral for repair.
  2. If the servo motor does not turn, and you have the correct voltages getting to the motor, that normally indicates that the motor is bad and needs to be replaced. You can usually purchase a servo motor at any satellite dealer.

If you find that the servo motor seems to be buzzing all of the time or if you are watching a program that seems to fade out intermittently and will come back by itself or if you change the channel up or down and back, the problem is also likely to be a bad servo motor. But try these steps to determine if the problem is more serious:
 

  1. Take the servo motor off of the feedhorn and hook it up directly to the back of your receiver. You must disconnect the wires going to the dish for this test to be valid.
  2. Watch the servo while you change channels, then let it sit for a couple of minutes. If it turns when you change channels and does not drift or buzz when you are not changing channels, that tells you that the receiver and servo motor are working properly and the problem is likely to be noise being pick up by your unshielded pulse line. The only way to correct this problem is to make sure that the pulse line is shielded and the shield is grounded at one end.
  3. If the servo motor behaves the same way when it is hooked up directly behind the receiver as it did out at the dish, then it is most likely bad. You need to replace it.
 
 

 

During my test the first decision I made was not to even bother hooking up the unit to my Drake 1724 c-band analog receiver. The sad truth is that so few analog channels remain that hooking the unit up was not even worth considering. My Drake 1724 is now 14 years old ,rebuilt once and is now the dish mover for my 12' c-band dish . However the Drake is not ready to be sent to "The Valley of Unwanted Toys" yet and with a new Von Wiese heavy duty mover installed this spring I hope to see many more years of service.

My Chaparral Polorotor 1E/A  was already attached to my dish so I simply removed the old feed horn. In removing the old unit I was careful to note the f/d ratio on the old unit. I put a piece of red tape on the new throat set to the proper f/d.

To calculate the focal distance, you have to measure the diameter (D) and the depth (d) of the dish. Measurements should be in like units (you can't use feet for the diameter and inches for depth). For the example, we will say we have a dish that is 144 inches in diameter (D) and 24 inches deep (d).

focal distance (f) equals the diameter squared (D x D) divided by 16 times the depth (16 x d) or :

D x D = 144 x 144 = 20736
16 x d = 16 x 24 = 384
D x D/16 x d = 20736/384 = 54

focal distance f = 54 inches

After you have calculated the focal distance (f), you can use that figure to calculate the f/D ratio of your dish. In this case, using the same diameter (D) = 144; and the calculated focal distance (f) = 54

f / D = 54 / 144 = .375
f /D = .375 which you would round up to give you a setting of .38

The list below shows how far the throat is out from the scalar rings for different f/D settings.
EXAMPLE: A dish with a .42 f/D will have the throat about flush with the rings.

Inches -- f/D
.12 ------ .42
.32 ------ .40
.52 ------ .38
.72 ------ .36
.92 ------ .34
1.12 ---- .32

 
Putting red tape in the BSC 621 made it easy to reposition on scaler ring 

The BSC621/2 was inserted into the scaler ring set to polar axis using the T5 satellite which is dead south here in Winnipeg..The unit was hooked up, I went inside to start scanning with my Viewsat Ultra. KCSG St. George,UT 3919 V 1962  3/4 was entered and scanned . I came back with a Quality of about 88 .

Next check T5 ku for international channels.. In Winnipeg 11836 V 20770  3/4 has a hot signal it is always a logical starting point for any T5 project.. I set up these values on the Viewsat Ultra. Usually you need to bump the over a bit off your c-band target--a couple of clicks and I had a reasonable signal. Q35. I went back to the dish twisted the unit about +/- 5 degrees off polar axis to get the maximum signal strength. I did a complete scan frequency by frequency rather than a pure blind scan. T5 has a wide variety of signals and I could not  pull the weak transponders 11874 .

On to AMC 4 /ku could not receive 12169 . G10R could not receive 11720 which tends to be weak here as well. All other satellite were scanned for c band and found all channels. One might think that by having a 12' c-band unit that I should have been able to get all channels listed in the Satco DX chart.. Not so -- my dish is 15+ years old and has been rebuilt with good used mesh last spring so some surface integrity problems exist. A 12'dish has a very narrow beamwidth and absolute accuracy is a must. Accuracy that just can not be obtained with equipment this old. However it is typical of the units most users will install this product on a good representation of what the average user can expect.
 
4DTV order BSC621
 
Viewsat or Coolsat HD 8000 BSC 621/2 . 

For $59 it is an excellent replacement unit. A Viewsat receiver and the BSC621/2 can put new life into your old dish.

 
Complete Project Updates 15 year old C-Band Dish