Input voltage spec and Return Loss Bridge questions

[videobruce]

The input spec for a Spectrum Analyzer that lists maxium dc voltage, how imprtant is this? Most scopes I have seen are in the range of 25-50vdc. There is one that lists it as "0 vdc". I don't understand how it can be "0" anything other than that tells me there can't be any dc voltage present.
How important is this spec and where/when would it come into play?

Next, I need a "Return Loss Bridge" for taking 'Distance to Fault' and VSWR readings. The device from the scopes manuafcture is ridiculously priced.
Anyone have suggestions of something much cheaper?

 

[fineshot1]

The input spec for a Spectrum Analyzer that lists maxium dc voltage, how imprtant is this? Most scopes I have seen are in the range of 25-50vdc. There is one that lists it as "0 vdc". I don't understand how it can be "0" anything other than that tells me there can't be any dc voltage present.
How important is this spec and where/when would it come into play?

Do you have a link for the analyzer you are in question about and can you specify the actual
spec parameter you are referring to(ie: page number and actual spec)? This does not sound
familiar so I am looking for clarification.

Next, I need a "Return Loss Bridge" for taking 'Distance to Fault' and VSWR readings. The device from the scopes manuafcture is ridiculously priced.
Anyone have suggestions of something much cheaper?

I too am looking for one of these but at the prices I have seen I won't be picking one up too
soon. These are precision instruments and you will pay a lot for one.

 

[videobruce]

I have another thread which dealt with the two SA's I'm looking at.
The one I was talking about here is this (.pdf file);
http://www.lptech.com/PDF Files/LPT-3000.pdf

Note on page three, the right side of the front panel the "0Vdc" rating at the input and on the last page. 2/3 of the way down, the same spec.
I re-questioned LP Technologies regarding this issue and the reply was;

On the DC issue I can assure after speaking with the my engineer in South Korea that the front end is capacitive coupled, I think this is a Korean to English translation issue which we will be changing the front panel overlay thanks to you bringing this to our attention.

at the prices I have seen I won't be picking one up too
soon.

http://www.rfimage.com/eagle.html
Well, that's half the price the scope's manufacture wanted. :roll:

 

[fineshot1]

Bruce - I am not sure what to tell you but I suspect this is a spec that involves possibly having DC voltage on a hardline cable for a tower mounted preamp or similar.

Go to http://batboard.batlabs.com/

login (create one if you do not have one) and go to the thread "Test Equipment & RF Equipment Alignment"
and ask the user "Wowbagger" in the Aeroflex forum about this. He is a very good fellow and extemely knowledgeable and can probably help you out. Good luck & please post back if you find out cause now you have sparked my interest.

 

[videobruce]

Ok, thanks for the link. Always looking for new forums.

FWIW; That Eagle RLB (1.3 GHz coverage) I found for $725. I also found a Anritsu 60n50 RLB for $650.

Still way too expensive.

 

[zz0468]

The input spec for a Spectrum Analyzer that lists maxium dc voltage, how imprtant is this? Most scopes I have seen are in the range of 25-50vdc. There is one that lists it as "0 vdc". I don't understand how it can be "0" anything other than that tells me there can't be any dc voltage present.
How important is this spec and where/when would it come into play?

The importance of the spec would be determined by what you intend to do with it. If you're just monitoring over the air signals, then it's not a factor. It's really just an indication of how much DC you CAN apply to the input without damage, as opposed to some critical spec that directly impacts operation or accuracy.

Next, I need a "Return Loss Bridge" for taking 'Distance to Fault' and VSWR readings. The device from the scopes manuafcture is ridiculously priced.
Anyone have suggestions of something much cheaper?

For 'distance to fault', you need a time-domain reflectometer, not a return loss bridge. Ridiculously priced? Not if you look at it in terms of the time and trouble it can save you on the job. Anritsu makes a device called the Sitemaster. It functions as a TDR and swept return loss bridge, with various other options available. Price class is $5k-15K, depending on how equipped, and the specific model. And they're considered one of life's little bargains by people who install antennas and feedlines for a living.

Suggestions for cheaper? Find one used on eBay or at any of the many used test equipment manufacturers. I have an old HP TDR that I bought for $100. It's NOT user friendly, but it IS quite accurate.

Edit: " used test equipment manufacturers"??? Duh... used test equipment VENDORS.

 

[videobruce]

The Spectrum Analyzer I'm getting has a tracking generator and the software/firmware to do the math for Return Loss & VSWR, all that is needed is this Bridge.

 

[N_Jay]

The Spectrum Analyzer I'm getting has a tracking generator and the software/firmware to do the math for Return Loss & VSWR, all that is needed is this Bridge.

If you are really good, all you need is a scope and a pulse generator.

 

[videobruce]

I'm not that good and don't have a pulse generator. :wink:

 

[zz0468]

The Spectrum Analyzer I'm getting has a tracking generator and the software/firmware to do the math for Return Loss & VSWR, all that is needed is this Bridge.

What about the necessary HARDWARE? The typical inexpensive Spectrum Analyzer / tracking generator does not have a built in directional coupler for single port return loss measurements. What is it you intend to measure with this device? They also don't typically give you distance to fault information. As stated above, neither does a return loss bridge.

 

[videobruce]

All the documentation states is the need for a RLB to make the measurments.

Receive only & 2-way VHF & UHF antennas systems and possibly TV antennas if a 50-75 ohm pad would work. I haven't investagated that part yet.

 

[zz0468]

All the documentation states is the need for a RLB to make the measurments.

Receive only & 2-way VHF & UHF antennas systems and possibly TV antennas if a 50-75 ohm pad would work. I haven't investagated that part yet.

That's pretty vague. Documentation for what? Are you just checking for continuity to the antenna, and that it's operating on the desired frequency? A spectrum analyzer / tracking generator will do that with a directional coupler which would be to allow you to use a two port device (spec an/ gen combo) to measure a single port device (antenna).

The RLB would allow you to make actual impedance measurements, which is seldom actually necessary in evaluating commercially manufactured antennas and feedlines. But there are some decent units manufactured for the amateur market that would fulfill that requirement.

You're asking for advise on stuff that you clearly don't have the background or understanding of, but only providing us really vague information to work with. You're not likely to get the help you need here.

 

[N_Jay]

Build/Buy a simple square wave generator.

Send pulses up the line, look at the line with a fast scope.

You should fairly easily see the return pulse. Get the time difference between the original and the echo, and the velocity factor of the line and there ya go.

 

[videobruce]

That's pretty vague.

Seemed clear to me. What don'tyou understand?

Documentation for what?

A SA as I just mentioned.

You're asking for advise on stuff that you clearly don't have the background or understanding

Which is why I'm asking here. I go to the school of Hard Knocks and I have no problem gaining knowledge and experiance on my own with a little help.

only providing us really vague information to work with.

I can only provide info that I have as I don't have the SA yet, it's has just been ordered. It is replacing one that I traded in.

As I already stated, this SA has a option for Return Loss and VSWR measurments which I wasn't orginally looking for, but it is included since this is a demo. Since it is there, according to their documentation all that is needed to make these measurments is a RLB, again as I stated. It just seems logical to take advantage of this and expand my knowledge as long as the additional cost isn't that great.

 

[wa8pyr]

Build/Buy a simple square wave generator. Send pulses up the line, look at the line with a fast scope. You should fairly easily see the return pulse. Get the time difference between the original and the echo, and the velocity factor of the line and there ya go.

There are circuit diagrams out there for building your own simple TDR to use in conjunction with a 'scope, and IIRC the ARRL has how-to's on their web page along with conversion charts and so forth. Been awhile since I've seen one but I know ARRL has featured TDR projects in QST magazine in the not-too-distant past.

The one at this link is pretty simple: http://www.epanorama.net/circuits/tdr.html

You might also check the ARRL Handbook, or the Antenna Manual; I've seen TDR circuits and how-to's in both of them.

 

[zz0468]

Seemed clear to me. What don't you understand?

Are you installing new systems? Maintaining old? Doing design work? Amateur? Commercial? How critical is distace-to-fault?

A SA as I just mentioned.

What wasn't clear is whether the docs for the test equipment you're looking at said that, or docs for equipment you're trying to maintain said that.

Which is why I'm asking here. I go to the school of Hard Knocks and I have no problem gaining knowledge and experiance on my own with a little help.I can only provide info that I have as I don't have the SA yet, it's has just been ordered. It is replacing one that I traded in.

That's fine. It's a good way to learn things, and I'd LIKE to offer suggestions, but finding that your requirements aren't being made as clear as you think they are.

As I already stated, this SA has a option for Return Loss and VSWR measurments which I wasn't orginally looking for, but it is included since this is a demo.

Ok... the picture is startin to emerge from the fog. I was reading that you had some item calling for a RL and VSWR in order to maintain it properly. As I understand it now, you're just trying to understand the specs of the item you're purchasing.

Since it is there, according to their documentation all that is needed to make these measurments is a RLB, again as I stated. It just seems logical to take advantage of this and expand my knowledge as long as the additional cost isn't that great.

Ok. NOW I understand. Yes, that is correct. The RLB would be required in order to use the SA for VSWR and RL measurements. Back to your original question, the factory price of the accessory RLB... you COULD find something on eBay that would work, but don't expect any published calibration or accuracy specs to hold.

And what of the distance to fault requirement? Is that your requirement, or is that something this device does?