- Noisy repeater output - 3 Updates
- Step Recovery Diodes - a blast from the past... - 1 Update
| Jeff Liebermann <jeffl@cruzio.com>: Jun 14 09:52AM -0700 On Fri, 14 Jun 2019 14:16:05 +0200, Eremita Analogico >> (noise) decreases. If it decreases more than -10dB, then it's being >> generated in the SA by your overload. If it drops exactly -10DB, then >> it's real. Please do the above test with a 10dB attenuator. If the spurious noise drops 10dB, then you have a real problem. If the noise drops more then 10dB, the noise is being generated inside the spectrum analyzer. >Thus, I think that the PA of Vertex VRX7000 has some issues, but I never >seen noises of that type. I wolud expect some harmonics. >The internal supply can do this noise? The spectrum analyzer picture shows that you are operating on 162.4 MHz. <https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg> In the USA, that's one of the weather stations broadcast frequencies. <http://weatherradios.com/stations-and-frequencies> I have no idea what 162.4MHz might be used for in Italy. You haven't supplied any additional information on the equipment you're using, duplex split frequency, and available test equipment. The HP spectrum analyzer will survive the obvious overload, but I'm not sure if it will produce usable measurements (without spurious noise). As I mentioned, try reducing the input level with an additional attenuator and see if the spurs disappear. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Ralph Mowery <rmowery28146@earthlink.net>: Jun 14 03:32PM -0400 In article <c8j7ge53nt8esk4tnud1nobvstis91b6av@4ax.com>, jeffl@cruzio.com says... > noise). As I mentioned, try reducing the input level with an > additional attenuator and see if the spurs disappear. > -- I have used a HP 8924C for a SA and sometimes it is difficult to tell if it is overloaded at first even though it has the high power option and will handle 100 watts. Sometimes to see the spurious RF you need to notch out the fundimental. |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 14 04:55PM -0700 On Fri, 14 Jun 2019 15:32:53 -0400, Ralph Mowery >I have used a HP 8924C for a SA and sometimes it is difficult to tell if >it is overloaded at first even though it has the high power option and >will handle 100 watts. I've had the same problem with every spectrum analyzer I've used. When brand new, the SA is probably quite linear throughout its specified dynamic range. However, after getting overloaded with too much RF causing components to fry, the dynamic range can be reduced somewhat. It's difficult to tell if something is broken, but the 10dB attenuator test I previously mentioned is a clear indication that either something is wrong or burnt out. Notice that the marker shows a signal level of 4.52dB (upper right of screen), but shows about +10dBm on the graticule. <https://i.postimg.cc/3JhhbHpC/IMG-3321-1.jpg> Kinda looks like the detector and/or the A/D converter that is measuring the marker level has gone rather non-linear. >Sometimes to see the spurious RF you need to notch out the fundimental. That works very well on UHF frequencies which have a 5MHz split between transmit and receive. Unless you have a rather large cavity handy, it works badly on VHF frequencies, where the split can be as little as 0.6MHz. For the present situation, the SA shows a span of almost 300MHz for a 161.4MHz center frequency. For all I know, the spurious noise could be switching noise, AM/FM/SW/TV broadcasting, other services, etc along with their intermod mixes. With a sweep from 0 to 300MHz, that's about what I would expect with a cliplead crammed into the antenna connector. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Paul Drahn <pdrahn@jodeco.com>: Jun 14 01:25PM -0700 On 6/11/2019 7:56 AM, three_jeeps wrote: > "The main phenomenon used in SRDs is the storage of electric charge during forward conduction, which is present in all semiconductor junction diodes and is due to finite lifetime of minority carriers in semiconductors." > Finite lifetime of minority carriers....I assume when switching from forward conduction to reverse the minority carriers are quickly reversed in their flow given the abrupt change of voltage polarity? > J Back then, TEK made many of their own diodes and transistors because they could not get the quality and specs they wanted. They later made their own ICs. We use one of their stencil machines today to screen solder paste on PC boards. Paul |
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