If you are trying to insert a "portable sweep" in the field through the -30dB resistive testpoint on the amplifiers (if you have Magnavox Mainstations) you MIGHT get lucky and get a sweep trace through, BUT, keep in mind that the isolation on these testpoint are extreemely poor and you WILL encounter a reflection that will cause a bogus reference. This bogus reference will carry through the cascade and you will see sweep traces that are NOT accurate. In the Magnavox Mainstation the only option would be injecting (forward sweep) through a backwards tap to simulate a output COUPLED testpoint as there are NO points within the motherboard to do so. As a matter of fact, forward sweeping should be done at the AGC port as it is a coupled point to eliminate reflections.
If you are using the GNA and TNA Philips/Magnavox stations, you have the same -30dB resistive testpoint on the "A" versions but do have a -20dB coupled testpoint in the "B" and "D" versions. Unfortunatly this does not help you as the coupler is in the WRONG dirrection for sweep insertion of the forward. Again, a backwards tap to simulate such could be used but is probebly more trouble than what it is worth. If you have a Stealth TX it would be easier to inject this in at the Headend and reference as needed at different locations in the field if at all possible.
If you are not concerned with keeping customers up during this test, one can be creative and do an insertion by removing the module and through DC's and such inject into the trunk.
Keep in mind that if you are using the SDA (Stealth) sweep, you will have problems doing a field injection as the sweep transmitter (normally in the headend) MUST see it's own sweep along with ALL existing carriers on the network as to build a channel plan and ignore and channels or carriers as not to confuse them with spectrum glitches.
Another option would be to use the SDA Stealth in the "SWEEPLESS" mode. This does not require a transmitter and is not as accurate and can be effected by the noise floor as it is not seeing transmitter sweep points or active channels that have been modified in the orginal channel plan as they otherwise would be corrected for. The SWEEPLESS sweep can be done by changing the MODE from SDA to SWEEPLESS and just reference the forward output level at a specified output testpoint. But as stated earlier, if you have a RESISTIVE testpoint, you generally are referencing into a REFLECTION and have trash as a result.
If you inject OR read a sweep off the set screw on any device it will produce such a MISMATCH that your refelection will be even worse...this is not advised.
If you are looking for "cable faults" you will need more a TDR and document such issues as not allcable faults can be found with a sweep.
I hope that this has helped.
Good Luck!
Greg Tobin
Interactive Broadband Technical Services, LLC
314-422-4423 cellular
Re: Pre sweep ug cable
Member #: 7190
Registered: 1996-2001
Posted:
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Name:
Greg Tobin
Name:
Greg Tobin
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Interactive Broadband Technical Services
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HFC Engineer/Consultant
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