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 on: Today at 04:20:56 AM 
Started by KF7DS - Last post by K1BQT
Try this experiment. Connect your EFHW through a matching network -- and install an efficient current choke at the 50-ohm feedpoint. Now, measure the SWR at the input of the choke across a wide frequency range with an analyzer. What do you see? How might you explain what you measure?  Wink


 on: Today at 03:38:24 AM 
Started by KF7ITG - Last post by K4PDM

That's probably a pretty fair assessment.  I don't think many of the radios produced in the last 15 or 20 years are going to be around in another 20 or 30 years like the stuff we see made in the 50's and 60's.

We thought that about the radios of the late 70s and early 80s with the special ICs and displays, and thanks to the web and the technical capability of hams, lots of them are still on the air.

If there's any way possible to keep a popular radio going, someone will find it.

 on: Today at 03:27:56 AM 
Started by W6EM - Last post by G8HQP
Quote from: W6EM
The BF908WR has typically over 40 and up to 50 mS of forward transconductance.  The BF998 is only about 24mS.  Although its not much, when you look at a 40673 for reference, a double, triple and quadruple of voltage gain might be worth it.  If I can find another device that comes close to mid 40's to 50 mS, then I'll abandon the BF998WR.  So far, nothing comes close that I could find.
Won't excessively high gain be a problem? Beyond a certain point it won't boost noise figure, which is largely set by the circuit. Very high tranconductance is useful in a wideband circuit, but we usually want narrowband preamps etc.

 on: Today at 03:20:01 AM 
Started by OH2EUU - Last post by G8HQP
If you want to adjust an antenna for zero reactance then you have to be at the antenna feedpoint.

If you want to adjust your transmitter load for zero reactance then you have to be at the transmitter.

Winding turns ratio is the square root of the required impedance ratio.

 on: Today at 03:19:14 AM 
Started by N0UN - Last post by PA1MR
Well, the article states:

'Seven months after we announced T31W a 3 man team from Europe activated T31 and made a total of 30,000 QSOs. Of the total, 5,000 QSOs were with Europe where T31 is one of the most needed entities. Subsequently, they announced their intention to return to T31 in 2017 to finish the job. Based on these events it makes no sense for us to commit personal or donated funds to continue the project' (TNX

It's a personal decision; 'it makes no sense to US..'. The demand in the world of course is still there, but to them two T31 expeditions made PRIOR to their T31 expedition is not worth the trouble. Apparantly they want to do something UNIQUE. It's their money, work and free time. Is that so difficult to understand?

I am very pleased to read the following information in that same article: 'When the news of this recent T31 activation became public we considered switching to one of two back-up DXCC entities. One that we’ve been in discussions with the governing agencies for over 2 years, and another that recently came into view. These alternatives are still under consideration.'

So instead of two T31 expeditions in 2017, we'll get T31T and (possibly of course) another very interesting DXCC entity. What's wrong with that? I'm not complaining ;-)

 on: Today at 03:17:41 AM 
Started by KF7DS - Last post by G8HQP
Quote from: K6BRN
So you agree with me, a dipole needs no separate counterpoise.  Thank you.
That was never in dispute.

How do you feel about a monopole?  Those seem to work fine in free space, too.
My feelings are irrelevant. As I said, you need two connections. If you can't see the second connection then you just have to look harder until you find it. Unless, of course, you live in a part of the universe where physics is different so antennas no longer have to follow Maxwell's equations.

And... "grounding the shield cannot be done without a feedline choke..."  Do you really mean "a feedline choke with a grounded shield works better for shield isolation than just a grounded shield" because grounded shields are used without an RF choke all the time and work just fine.  sooo....?
I mean a coax feeding a dipole needs a choke if it is to be grounded. If you ground one side of a dipole feed without a balun then you have converted the dipole into a monopole.

Regarding placing an antenna perpendicular to a ground plane - any ground plane - man made or actual ground - produces an electrical mirror image of a resonant antenna and improves performance.  In fact, a monopole placed over a perfect ground acts as a dipole.
No, a grounded monopole does not act as a dipole - although many of the simpler antenna books may say that it does. A monopole has half the input impedance of the corresponding dipole. In addition to providing the second connection so somewhere for the current to go, ground also provides a mirror which modified the radiation pattern. Ground still does this mirror role for a dipole, or an elevated monopole with radials, or a loop. Don't confuse the two quite different roles of ground: second connection, mirror.

You are wrong about non-resonant antennas with a fixed tuning network, like the CHA-250B benefiting from radials or being placed on the ground.  I've experimented a great deal with this antenna, and it prefers to be isolated from ground as much as possible for the reasons I've stated above.  And the manufacturer agrees.
I am not familiar with any commercial antennas. I tend to ignore statements by antenna manufacturers; some of them are misleading, some of them don't understand antennas themselves, maybe some of them hope their customers don't understand antennas. Raising an antenna will modify its vertical radiation pattern. Raising an antenna may reduce ground losses. Raising a monopole antenna used with no radials will invite feeder radiation; the return current must go somewhere and if necessary it may even have to pass through a choke balun.

BTW - regarding circulating currents, you are forgetting the radiated energy in an EM field, much of which never returns to local ground, and most of which does not, in free space.
Not at all. At the antenna feedpoint there has to be a current loop, even if part of this loop consists of displacement current. There has to be two connections, as you need two connections to impose a voltage; there is no such thing as 'a voltage'! Radiation satisfies Maxwell's equations. All I insist on is that antenna's do too.

 on: Today at 03:13:07 AM 
Started by OH2EUU - Last post by OH2EUU
A simple question... when adjusting an antenna for zero reactance at the desired frequency, should I be using the analyzer at the feedpoint (without the coax feedline) or at the rig end of the coax feedline?
A less simple question: if the magnitude of impedance at resonance is something other than a 50-70 ohms requiring a 1:1 balun, or say 200 ohms requiring a 4:1 balun, how do I calculate the torroid windings required for making a suitable balun to achieve a 50 ohm match? (e.g. if my impedance is say 150 ohms?).

Yours sincerely,
Pete T

 on: Today at 02:46:38 AM 
Started by VK4FFAB - Last post by VK4FFAB
New version of the software has been released, backspace key now works for editing call signs being entered into log and some minor other code changes.

 on: Today at 02:36:48 AM 
Started by K9ZF - Last post by SV1IYF
Valid, no doubt, your suggestion WB6BYU, but I fear not that conclusive.
First, if an analyzer is at hand there is no need to resort to bulbs.
Any carbon, or better metal film resistor, will reveal the unknown ratio.
Now, in the event an analyzer is not available, the rig can serve plan B.
I just measured a 100W-230V bulb.
At almost rated voltage i.e. 225V it exhibits a resistance of 550 Ohms (225V/0.41A)
Same bulb measured with an Ohm-meter shows circa 40 Ohms.
There is an order of magnitude-plus change.
Consequently, one needs some guidance as to where this resistance stands.
Here, the rig's output power setting can prove useful.
Set it to 75W plus Watts (say 80W), to account for the cable and balun losses and check whether the bulb glows bright or dimmed.
More conclusive I think than trying to guess what it's resistance is at an intermediate point and how this should be translated to SWR.

 on: Today at 02:08:43 AM 
Started by N0UN - Last post by VK3BL
This is free world if i want to go to Bouvet next year  i will go . 
and i dont care if somone say ''Don't go becouse we are going there in 2018''

Yes, my friend.  I wish you success, whatever you do.  But there are never enough DXpeditions.  I don't understand how anyone can say there are too many of them to anywhere.

I agree.  The notion that T31 is now not needed is ridiculous.  Its #16 global / #10 EU on clublog right now.

But pse Dom, BS7H!  I am not sure if anyone else could do it but Rebel DX Group!!! Smiley  I would love QSL card before it gets turned into an airport!

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