[Lowfer] SIW (WM) in CT

Sat Jan 14 15:01:40 EST 2017

Mike

Roger all. The corrugated material for the solenoid coil was a good idea.

Assuming the honeycomb coils are high Q (no reason to think they're not) and the antenna tuning 
isn't extremely sharp there two possibilities. Could be either, or a combination of both.

1) The antenna isn't really at resonance. One can be fooled by small peaks and valleys off 
resonance. These are caused by the myriad of 'stray' capacitances / inductances in a big loading 
coil. There is never a doubt when resonance is hit because of the dramatic sharp peak in antenna 
current. Hand capacitance anywhere near the coil will easily detune the system.

2) Overcoupling of the exciter. Coupling into a large honeycomb coil seems problematic but I guess 
it could be done if one could get to each of the turns up from the ground end of the coil. It would 
probably be easier to have a small solenoid 'coupling coil' between bottom of the honeycomb coil and 
ground to make things easier. The tap is not going to be but a few turns above ground.

If you have a general coverage receiver start with that connected to the antenna looking for a 
dramatic peak in background noise. Don't necessarily expect it to be close to the 'design' frequency 
(calculated from antenna capacitance and loading coil inductance). If a dramatic peak in receiver 
noise isn't noticed reduce coupling - less turns between ground and the tap point and run the 
receiver test again. A piece of coax between the antenna and the receiver in the shack makes this 
test a bit more comfortable this time of year!

Jay

----- Original Message ----- 
From: "N8OOU" <n8oou at meekfarm.us>
To: "Discussion of the Lowfer (US, European,& UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Saturday, January 14, 2017 1:30 PM
Subject: Re: [Lowfer] SIW (WM) in CT

> Jay,
>
> What you were looking at was the 2015/16 setup using the solenoid coil. A direct link to the 
> current configuration is;
>
> http://wmbeacon.meekfarm.us/LowferBeacon2016.html
>
> For the solenoid coil the inner coil that I adjusted up/down for tuning is part of the equipment I 
> got from Warren / Bill Ashlock. It was wound with unknown spec Litz wire and supplied about half 
> of the needed inductance. As I wound the outer coil, I made the 10 count taps, not knowing 
> anything better. When I set up the antenna, I prodded the coil to find the best tap point.
>
> For this seasons coil I didn't make any builtin taps, just prodded after installation.
>
> For what it's worth, the corrugated coil form was made from the translucent plastic roofing panel 
> you find in the big box hardware stores. The air gap behind 80+ percent of the wire seemed like a 
> good idea, plus you can make the coil any diameter you need.
>
> 73   de   N8OOU - Mike Meek
>
> On 01/14/2017 06:37 AM, jrusgrove at comcast.net wrote:
>> 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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