Search found 67 matches

by DaveSt
Thu Dec 13, 2018 2:55 am
Forum: FM Radio
Topic: High Reflected Power Puzzle
Replies: 33
Views: 2127

Re: High Reflected Power Puzzle

It looks like the PA is oscillating by itself, which is not unusual in some PA designs. If the drive to the PA section is removed, most likely it will carry on oscillating. When the MOSFET was changed, if the bias current was not set correctly then that can make the PA more likely to take off like t...
by DaveSt
Wed Dec 12, 2018 12:23 pm
Forum: FM Radio
Topic: Harris Z FM Diagnostics Failing
Replies: 4
Views: 509

Re: Harris Z FM Diagnostics Failing

With any diagnostic system there is always the possibility that the fault indicated is caused by something unrelated to the error shown. It is worth checking everything else in with the transmitter and its output to make sure they are good. If you have a test load, try the diagnostics with it runnin...
by DaveSt
Wed Dec 12, 2018 1:37 am
Forum: FM Radio
Topic: High Reflected Power Puzzle
Replies: 33
Views: 2127

Re: High Reflected Power Puzzle

The problem with the design of antenna you have is that they are extremely narrow band. That can be quite challenging for any transmitter to drive. It increases the likelihood of instability in the transmitter PA. That may also have been made worse after the change in transistor. The instability wil...
by DaveSt
Wed Dec 05, 2018 11:44 am
Forum: FM Radio
Topic: Horizontal or vertical
Replies: 8
Views: 1003

Re: Horizontal or vertical

I do not know if Aldena have an agent in the USA, but they have a good crossed LP antenna for this:

https://www.aldena.it/index.php/compone ... 2-91x.html
by DaveSt
Fri Nov 23, 2018 12:09 pm
Forum: Broadcast Engineering News
Topic: Tiger Mountain (WA) master antenna catches on fire
Replies: 21
Views: 2824

Re: Tiger Mountain (WA) master antenna catches on fire

...Another question is why was there no pressure monitor on each transmission line along with a run monitor on the pressurization system. If I lost pressure on a large transmission line I would shut down the transmitter. It must be top of the list of replacement items... Looks like between ATC and ...
by DaveSt
Thu Nov 22, 2018 1:39 pm
Forum: Everything else
Topic: GOBBLE, GOBBLE!
Replies: 12
Views: 1063

Re: GOBBLE, GOBBLE!

Of course ,we do not celebrate it here, but best wishes for Thanksgiving everyone!
by DaveSt
Thu Nov 22, 2018 1:37 pm
Forum: Broadcast Engineering News
Topic: Tiger Mountain (WA) master antenna catches on fire
Replies: 21
Views: 2824

Re: Tiger Mountain (WA) master antenna catches on fire

kkiddkkidd wrote: Thu Nov 22, 2018 8:57 am

I had also incorrectly assumed that the radome material wasn't flammable but I guess it at least WAS moreso than I imagined.
I was surprised to read that too. The radomes I see are invariably fibreglass and do not burn.
by DaveSt
Thu Nov 22, 2018 12:57 am
Forum: Broadcast Engineering News
Topic: Tiger Mountain (WA) master antenna catches on fire
Replies: 21
Views: 2824

Re: Tiger Mountain (WA) master antenna catches on fire

Failure of a single antenna in a 32 antenna system may not have have caused enough of a VSWR fault to cause a shut down anyway. Apart from that, VSWR protection may not be fast enough to detect arcing anyway.
by DaveSt
Mon Nov 19, 2018 1:25 am
Forum: FM Radio
Topic: ERI COG-1084 question
Replies: 8
Views: 858

Re: ERI COG-1084 question

There are lots of things that can cause problems like this. Answering your question though, panel antenna systems will have a small frequency dependent variation, but it should not be significant. Unless that is you have an intended null in the pattern to protect another station. Variations in that ...
by DaveSt
Mon Nov 12, 2018 12:47 am
Forum: Broadcast Engineering News
Topic: Tiger Mountain (WA) master antenna catches on fire
Replies: 21
Views: 2824

Re: Tiger Mountain (WA) master antenna catches on fire

Makes a case for a split feed to the panels. Most master antenna systems I've been involved with have a line to the top half and a line to the bottom half that can isolated in case of a failure. ...Lee The photos do show a dual feeder arrangement for this system. With the amount of damage that woul...
by DaveSt
Sun Nov 11, 2018 1:26 am
Forum: Broadcast Engineering News
Topic: Tiger Mountain (WA) master antenna catches on fire
Replies: 21
Views: 2824

Re: Tiger Mountain (WA) master antenna catches on fire

No VSWR shutdown? Depends on what type of combining system is in use. In a balanced combiner system the TX won't see any VSWR mismatch coming from the antenna. I've always wondered why it's not common practice to monitor the VSWR of the combined output, where antenna faults can be detected and tran...
by DaveSt
Sat Nov 10, 2018 3:15 pm
Forum: Broadcast Engineering News
Topic: Tiger Mountain (WA) master antenna catches on fire
Replies: 21
Views: 2824

Re: Tiger Mountain (WA) master antenna catches on fire

It is hard to imagine the failure mode that could have caused all that damage to every panel. It's a lot of RF and on 6 channels, so lots of volts too. Maybe a VSWR issue causing voltage breakdown at the antennas? Some clear photos here: https://www.radioworld.com/news-and-business/tower-fire-disrup...
by DaveSt
Sat Oct 06, 2018 9:44 am
Forum: STL Engineering
Topic: RVR PTRL-LCD transmitter PS
Replies: 7
Views: 1467

Re: RVR PTRL-LCD transmitter PS

An old saying: Google is your friend, or in this case Bing. A search for the power supply part number finds this manual: http://3-mtr.info/manuals/RVR/TEX30LCD/M2TEX30LCD28NS.pdf The TEX30 has the same PSU and has the circuit diagrams you need. For safety, check R4 first and make sure there is no vo...
by DaveSt
Fri Oct 05, 2018 12:22 am
Forum: STL Engineering
Topic: RVR PTRL-LCD transmitter PS
Replies: 7
Views: 1467

Re: RVR PTRL-LCD transmitter PS

The circuit diagrams for the supply are not in the manual. There is a good chance that RVR will not even have them. In additions to the checks mentioned earlier, look for a high value resistor on the primary side of the supply. It will be connected to the unregulated DC supply capacitor and provides...
by DaveSt
Wed Sep 05, 2018 9:00 pm
Forum: FM Radio
Topic: Synchronizing FM over IP?
Replies: 11
Views: 1142

Re: Synchronizing FM over IP?

The delay needs to be kept within microseconds. The article I mentioned earlier is available here: https://www.waveart.it/leggi-news?id=51 . It is pretty good as they have understood what is needed well and have verified it with tests. To keep the modulation identical, they also say that the composi...