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   Home   Help Search  
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 51 
 on: Today at 03:42:43 PM 
Started by ZL1BBW - Last post by W1QJ
Good, more often than not a G-F short will not show up on a simple cold ohm meter test.  The grid literally needs to be broken.  Most G-F shorts only show up when the filament is hot and migrates and touches the grid and then ZAP.  Best way to check for a G-F short without damaging anything is to use a Variac and monitor the grid current as you bring up the line voltage slowly.  You will eventually see negative grid current on the meter.  As soon as you see the meter go negative you know one of the tubes is bad.  Remove one at a time and recheck.  When the meter does not swing negative you have found the bad tube.  If you switch over to self bias you can ditch the 50K resistors.  The smaller resistors across the caps will act as bleeders.  You will not have any ALC voltage if you ditch the 50K resistors but you do not need ALC anyway.  If you really need ALC yu can use the 24vdc relay voltage for that, just change the divider in the ALC network.  But if you only have 100 or so watts of drive AlC is not needed.

 52 
 on: Today at 03:38:01 PM 
Started by AA6BQ - Last post by WB8VLC
http://www.trcelectronics.com/View/Mean-Well/SE-600-48.shtml


I used to eval LDMOS devices FOR FREESCALE in TEMPE AZ. until this summer and I was using various Mean-Well supplies including the above 48 volt 600watt supply for a MRFE6VP6300, 300WATT HF/6 meter amp that I designed.

The above supply has an  11% overhead on rated current handling or it's actually capable of providing 660 watts.

2 of these supplies are used to power a similar MRFE6VP5600, 600 wattr HF/6 METER amp.

 53 
 on: Today at 03:34:44 PM 
Started by VE3NEA - Last post by VE3NEA
When we listen to weak signals in the noise, sometimes we "hear" our callsign even if it was not sent. Here is why:

https://www.youtube.com/watch?v=0bG7EFhMw8w

Funnily enough, even CW Skimmer sometimes behaves that way.

73 Alex VE3NEA

 54 
 on: Today at 03:30:22 PM 
Started by W6GX - Last post by N1UK
When I realised that it was their log error. I put my logs back to original and will add a dupe QSO with the "matching QSO time" if needed at a later date.

Mark N1UK

 55 
 on: Today at 03:28:17 PM 
Started by LOWLYTECH - Last post by LOWLYTECH
thanks guys for all the input.  I will have to try to string some wire to see if I can receive anything with this unit.  I don't have a mic or key so that's good to know that I would have to have those to make the cw and ssb modes show any output.  Really looking forward to getting some time to sit down with the manual and learning what everything is for.

 56 
 on: Today at 03:25:48 PM 
Started by KJ6TSX - Last post by KJ6TSX
Hi
I was playing around the other night and made a 2 meter dipole, I checked it out with the antenna analyzer and dialed it in for 146.925  my favorite repeater. seemed to work OK in the shack with my handi talkie.
So I brought it up to my favorite hill top were I knew the HT would just hit the repeater with a rubber duck, and it did. But my new antenna would not?? checked my coax for shorts-none, coax loss 1.7db.
I tried the antenna in the vertical position (ground down feed line at right angles to elements more than a 1/2 wave) even tried horizontal.
My swr is 1:1 at 146.925 at 57 olhms with a 31 inch piece of rg8 coax when testing antenna, when in operation add a 10 foot piece of rg316

So what am I missing

Thanks for the help
KJ6TSX

 57 
 on: Today at 03:23:56 PM 
Started by AI4WX - Last post by WB6BYU
Quote from: AI4WX

i have about a foot and half of rg58 with no ends. whats the best way to measure at the base of an antenna? can i use a reallly short piece of the rg58 say about 6 inches to test my antennas with?




At VHF a double-male connector might be short enough, but probably not at UHF.

In that case, try adjusting the antenna length, radial lengths, radial tilt angle, etc. for minimum
SWR.  In the end, that is what will make the reactance term disappear, because when the antenna
matches 50 ohms there won't be any reactance.  In the end, low SWR is what matters (though
you're approaching the point where you won't see any improvement in performance as you lower
the SWR.)

If you want to know what is actually happening at the antenna, correct your readings for the
coax length using TLDetails or a similar program, or from a Smith Chart, etc.

 58 
 on: Today at 03:23:37 PM 
Started by N0UN - Last post by N5VYS
Nice video!

Obie-N5VYS

 59 
 on: Today at 03:16:01 PM 
Started by 4L5A - Last post by N5VYS
As always, I could use the band fills!

Obie-N5VYS

 60 
 on: Today at 03:13:06 PM 
Started by KM4CIV - Last post by WB6BYU
There isn't a one-size-fits-all answer.  On 20m and up, where the antenna can be close to
full size (especially if you use the 16' telescoping whips) efficiency can be quite good.  On
the lower bands, especially when the antenna is less than half of full size, efficiency drops
considerably.  Eventually you get to the point where you can run 100W into the antenna
and still radiate a QRP signal!

Tilting a dipole may provide some directivity, but unless you are over very good ground
(or salt water) you may find that the peak of the pattern is still weaker than a standard
horizontal dipole.

If you want directivity and gain, then adding a parasitic element to make a 2-element
yagi is probably the best approach, but the losses build up even faster than with a dipole,
so you need to be close to full sized to actually achieve much gain.  Element tuning is
also important, and that can be difficult to get right for parasitic elements.


We've used Buddipoles a couple times on ARES exercises.  What impressed me the most
(and not favorably) was how much work it seemed to take to get them tuned:  I don't
know how many times we had to put the antenna up, measure the SWR, take it down,
adjust either the loading coil or the length of the telescoping whip, put it back up, check
the SWR, etc.  On one hand, this means the telescoping pole is fairly easy to work with,
but it seemed a horrible waste of time.  Then I was reading the comments on the web
site and saw how many users carried an antenna analyzer or similar tool in the field
with them to tune the antenna.  This is supposed to make it easy???

I use wire dipoles for my portable antenna kit.  I set them up in a local park some time
in the late 1970's and tuned them for minimum SWR, and haven't adjusted them since.
I just string them up, connect the coax to the rig, and transmit.  True, they have been
installed in some rather "non-standard" situations in that time, but I don't bother
adjusting them or using a tuner.  A set of such dipoles hanging off a telescoping fishing
rod, a tree, a painter's pole, or a set of sectional tent poles make life simple.

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