HP 11693A limiter broken...? - Page 1
Forum section: electronics / repair

author: ytterligare
author_rank: Regular Contributor
timestamp: April 28, 2023, 06:20:12 pm
content: Hello, a couple of years ago I got this limiter from eBay, to protect my HP 8563A.Now, fun fact, I thought I lost it ever since as I wasn't able to find it in my room until today ( I'm a bit messy, I know...).So I decided it was worth a check on it to see whether it could really "level" the amplitude of the signal at the SA ingress or not.Now, from Keysight specs :- Frequency range 0.1 to 12.4 GHz, useable to 18 GHz- Guards against input signals over 1 milliwatt up to 1 watt average power and 10 watts peak powerIn my noob mind, it was reasonable to think it could level to 0 dBm the signal > 0 dBm.I'm sad to report I probably got a lemon, as I could not even test its performance due to the fact that the insertion loss is too big ( a.k.a. I think it is broken ) as per the following table :WITHOUT Limiter, HP 8672A Signal Gen Ampl. = 0dBm -> good cable -> peak amplitude read on the 8563A :100 Mhz -> -0,17 dBm300 Mhz -> -0.67 dBm1 Ghz -> -0.67 dBm2.1 Ghz -> -1.17 dBm4 Ghz -> -1.17 dBm8 Ghz -> -1.33 dBm12 Ghz -> -1.50 dBm18 Ghz -> -3.83 dBmWhile,WITH 11693A Limiter:100 Mhz -> -39.67 dBm300 Mhz -> -31.17 dBm1 Ghz -> -20.33 dBm2.1 Ghz -> -18.50 dBm4 Ghz -> -9.5 dBm8 Ghz -> -6.17 dBm12 Ghz -> -4.67 dBm18 Ghz -> -6.17 dBmAnyone had the chance to crack it open a specimen before and was successful in repairing it, or at least any idea what to look for ? In my opinion, with frequencies > 10 Ghz, it seems to be working well or generically speaking, it seems to perform better the higher in frequency I go...TnxAndyP.S. : I should have known something was fishy, as the eBay listing picture was showing a different limiter ( different s/n )

author: MaxFrister
author_rank: Regular Contributor
timestamp: April 28, 2023, 10:42:04 pm
content: I always assumed that it could limit (i.e., shut off) and never thought it could "level" to 0dB.What happens if you try a bit lower power, say -10dBm.I have a limiter (not sure the number off the top of my head) but I can check this evening.

author: ytterligare
author_rank: Regular Contributor
timestamp: April 29, 2023, 03:38:26 pm
content: Quote from: MaxFrister on April 28, 2023, 10:42:04 pmWell it might be because I'm not native English language speaker but in this case I assumed they meant the same, limiting the output at a certain level ( in this case, for the HP limiter -> +0 dBm ).Turned out that maybe the "leveling" is not that precise : take a look at the graph for my other limiter : you'll notice by the lower left graph that once the power in reaches +13 dBm it tends to be leveled to that power ( maybe a couple of dB more ) until maximum acceptable input power is reached, which is +33 dBm .These data/graph are taken from Mini Circuit's site, and I don't have any for the HP limiter, but I guess inputting +0 dBm shouldn't be out of the specs of the limiter....A.

author: MaxFrister
author_rank: Regular Contributor
timestamp: April 30, 2023, 03:51:23 am
content: I think the HP part would have a similar kind of graph, but shifted down. The minicircuits says it limits to 12dBm whereas the HP limits to 1mw (0dBm). Since you are testing right at 0dBm I think you are seeing a reasonable result.I do have the same part. If you'd like I can run some (non-destructive) tests if it would help.

author: ytterligare
author_rank: Regular Contributor
timestamp: May 19, 2023, 02:38:53 pm
content: Quote from: MaxFrister on April 30, 2023, 03:51:23 amMax, sorry I missed your kind offer !! Please do run a test for me on your limiter, if it's not too much a trouble...In the meanwhile, normalizing to take into account cables and adapters, I have run a transmission test through the VNA, only 100 Mhz to 3 Ghz, 0 dBm...not much of a difference...and to me this looks like a piece of junk...While theMiniCircuits, on other hand.... :CiaoA.EDIT : corrected and unified Scale/Div