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Checking a Balun with a DVM?

996 views 13 replies 10 participants last post by  holl_ands 
#1 ·
Hi Team,

Is there any reasonable way to test a Balun using a DVM? Does measuring connectivity (or lack of) give any reasonable indicator of the balun's health?

As an example, using a DVM on my XG91 balun, I measure:

Connectivity between the two elements that connect to the rear of the balun.
Connectivity between the center conductor on the coax connector and both elements
NO connectivity between the coax connector ground and the center connector on the coax connector.
NO connectivity between the coax connector ground and either of the elements attached to the rear of the balun.

Does this indicate anything? Should there be connectivity between the coax connector ground and the center conductor or either of the elements?

Thanks
Dan
 
#3 · (Edited)
Been a long time since I last took a look inside a balun. As I recall it was a simple ferrite core with twisted pairs running through a couple of holes and only a single turn. The grounds were on one of the lines of the pair and center conductor on the other line. You might be able to find a basic schematic on-line if you google. Say: http://my.integritynet.com.au/purdic/baluns.htm
 
#4 · (Edited)
It depends specifically if you have an "old" pre-2010 unit or the "new" version.

The "old" version simply had a standard matching transformer aimed out the rear of the housing. I think I've still got on in my garage at home if it neds to be checked...maybe...

For anything manufacture since 2010, that function was replaced with a PCB balun. It will measure exactly as you described.

If you're going to reinstall the element, do yourself a favor and drill a pair of small (1/16") weep holes in the bottom of the housing to let any water out that might make it in. Spacing the holes between the coax connector (and the blank spot in the molding) will work fin and you won't hit the PCB during the drilling operation. We replace maybe one or two 91XG baluns a month so it's not a big problem. I've recommended to the product manager that weep holes be added back to the housing whenever we make a new production run. They were there with to pre-2010 version but got lost when the injection mold was re-done for the bottom-exit F-connector.

Any questions, we have folks who work here 7 days a week to answer those questions. If any question needs elevation, they usually come to me, I just happened to drop in and see this particular thread. If you need SPECIFIC assistance with your 91XG, just fill out the contact form on our website (https://www.antennasdirect.com/customer-help-service.html) as those usually come through me first and we'll assist you.

Note: This thread is essentially an extension of your other one. Ask a moderator to merge them.
 
#12 ·
I didn't supply a photo of the other side because there's nothing there except an F connector.

Attached are loss displays on UHF for the original 91XG ferrite balun, the newer PCB balun and my homemade coaxial balun. All measurements are two baluns back-to-back so divide by 2 for the loss of one balun.
 

Attachments

#11 · (Edited)
#10 · (Edited)
#13 ·
For the heck of it I used a meter on an old --maybe 30 year old-- Channel Master balun and both of the 300 ohm side show conductivity to the other lead and neither 75 ohm side connects to any other lead. Looks like an old balun measures the same as the OP's. Not that it is a very good balun, but that is another issue.
 
#14 ·
OUTDOOR Baluns "typically" have DC continuity in between ALL Input and Output connections (or at least from both 300-ohm Twinleads to the Coax Shield). This is so that Static Electricity built up on the ACTIVE Elements can be drained off via the [NEC mandatory] Coax Grounding Block. And most INDOOR Baluns do NOT have DC continuity between Input and Output connections. An OHM meter only measured DC continuity and are nearly USELESS to ascertain RF PERFORMANCE....for example an internal short in a Conventional Balun's winding [ZAP!!!!] would NOT be detected....
 
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