[Lowfer] SIW (WM) in CT

[jrusgrove at comcast.net]

Mike

Not sure if 
I'm seeing the latest stuff on your website or not ... a corrugated form for the main coil and a 'variometer' that slides in and out of the main coil?

#14 THHN is perfectly fine for a loading coil considering typical ground losses etc ... you will be hard pressed to see any difference going to Litz.

Broad tuning would indicate that you're 
either not really at resonance or the coupling in incorrect. Even with 170 ohm 
total R (if that's what it turns out to be) tuning should be quite sharp. 'Hand 
capacitance' should detune the antenna from resonance. It should be difficult to hit the peak and keep it there. The 'twitchier' it is the better it is (higher Q)!

In looking at the pix of the corrugated form coil it would appear there's 
not nearly enough turns for the inductance required. Maybe the pix was taken 
before the winding was complete? You also mention that there are taps every 10 
turns for the feedpoint. The proper tap point is going to be far more critical 
than that and probably 
won't even be 10 turns above ground - more likely just a few turns above ground. The correct tap point may be critical to within a half turn or less. (That's 
why I prefer a multi tapped ferrite toroid core for coupling).

One can check for resonance by attaching a receiver in place of the 
transmitter. The receiver noise should show a definite and sharp peak at 
resonance.

Jay W1VD  WD2XNS  WE2XGR/2    





----- Original Message -----
From: N8OOU <n8oou at meekfarm.us>
Reply-To: Discussion of the Lowfer \(US, European, & UK\) and MedFer bands 
<lowfer at mailman.qth.net>
To: Discussion of the Lowfer \(US, European, & UK\) and MedFer bands 
<lowfer at mailman.qth.net>
Sent: 1/14/2017 12:06:15 AM
Subject: Re: [Lowfer] SIW (WM) in CT


Garry,

I have suspected the loading coil is my biggest problem. I installed my 
3rd version loading coil for the 2016/17 season, wound as a universal 
coil with three "pies". Those details are on my webpage.

My original coil gave me 35-40 mA, 2nd gen (used last season) gave me 
50mA, and now this one at 75. All versions were able to be tuned, but 
the tuning was very broad. Body capacitance did not affect the tuning 
much. On the other hand, once tuned, the performance stays stable.

I am in the process of constructing a 4th version. All previous 
versions were wound using awg 14 THHN. For version 4, I have purchased 
108/40 Litz wire manufactured specifically for 100-200 Khz. That was 
very expensive, and my spouse is barely speaking to me. I finished 
winding that coil last night, and have been testing it on the bench 
today. With a variable cap to resonate the coil at 185 Kc I was able to 
light 6 NE-2 bulbs with just a 3VPP drive from my signal generator.

Tomorrow, I will construct the tuning coil and gimbal mount. I hope to 
wrap this up soon and get it on the air.

73 de N8OOU - Mike Meek

On 01/13/2017 08:13 PM, Garry wrote:
> Mike, I notice you mention your normal lowfer antenna current is about
> 75 ma. With 1 W input that implies a quite high net resistance of about
> 178 ohms. Ground resistance is certainly a part of that but I wonder if
> your variometer to resonant the antenna is an even bigger source of
> resistance. The first variometer I wound used run of the mill magnet
> wire and had way too much DC resistance when enough turns were wound to
> reach the roughly 2mH needed for antenna resonance. I eventually got
> some decent litz wire and lowered the resistance to around 10 ohms. I
> don't recall the total system resistance I ended up with but I'm sure
> the antenna current is at least 150 ma. So 
I'd suggest you measure the
> DC resistance of your matching inductor (yes, the AC resistance at 185
> kHz will be somewhat different) and if it's 
high consider working on
> that first. It's surely much easier to improve than the ground system,
> at least in the winter, hi.
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