[Lowfer] Beacon "IO" QSY to 185299.2

Mon Feb 8 20:00:12 EST 2010

Craig I set my lowfer ant up as you are doing. First I resonated it then 
tapped up from the botttom for a 50 ohm match. Two pieces of test equipment 
that were usefull were:
an impedance bridge straight out of the hand book, this is simple a bridge 
with 50ohm resistors and a 1kpot. a diode 50ua meter and a box is all thats 
required. It can be calibrated with resistors.
I drove it with a Ramsey digital gen but an audio gen would work as well, 
most go up to 1mhz.

an swr bridge we used the coupler from a CB bridge and replaced the 0-1ma 
meter with a 50ua meter.

for rf current I use a ft37 core with 19 turns of wire in the secondary in 
series with a 1n914 diode and a 50ua meter for the pickup. the antenna lead 
is the primary, passing through the center of the pickup coil.
I started with 45 turns and reduced the turns as I made improvements.
The pa0rdt mini whip( google pa0rdt) makes a good mobile or portable 
antenna.

Lots of info on the internet google phrases like lowfer, lowfer antenna, 
1750 meter ant. yord should find them. One trick I saw was a small coil of 6 
or 8 turns 1/2in id in on the ground lead with a ferrite rod to vary the 
inductance.
Early on I used ne2 bulbs for an rf indicator.

Good luck.

Paul k5wms
----- Original Message ----- n
From: "craig wasson" <craig at wasson.com>
To: <lowfer at mailman.qth.net>
Sent: Monday, February 08, 2010 1:14 PM
Subject: Re: [Lowfer] Beacon "IO" QSY to 185299.2

> Pardon the newbie questions on the list - but I'm hoping my experience 
> will
> help some other lurker newbies.  The transmitter is an LF-90 from North
> Country Radio - a newish offering from them that includes a built-in CW 
> IDer
> which makes a nice convenient package with nothing needed but the 4"x4"
> board, a power source and antenna.
>
> Looking at the schematic it seems to be a Pi network on the output side - 
> so
> I think it would want something pretty close to the design load of 50 
> ohms.
> It's been the better part of half a century since I have been homebrewing
> transmitters and playing on longwave, so I'm having to re-learn a lot and
> dig out my old books.
>
> My concern about just linking to the antenna coil with a few turn loop 
> would
> be knowing exactly how many turns it would take to get something close to 
> a
> 50 ohm load on the TX.  This is why I was trying to ground the base of the
> coil and tap it.  My theory was that somewhere a few turns up the coil I'd
> find a 50 ohm point.  However my experience is mostly with 160M verticals
> and longwires.  Extremely short antennas seem to confuse the math.  Maybe
> that trick only works with antennas which have a feed point above 50 ohms?
>
> The beacon is unattended while I'm working this week, so any adjustments
> will have to wait until Thursday evening.
>
> I will be removing a section of turns from the middle of my 6" diameter 
> coil
> to drill a hole for a shaft - I have a 4" section of PVC I plan to wind
> about 50 turns on and mount on this shaft to turn it into a variometer.
> This should let me tune more accurately, although I think I'm pretty close
> already.
>
> I'll try simply tapping a few turns at the base for a feed point and see 
> if
> accurate resonance helps.  Then I'll try a separate feed loop and compare
> results.  Any suggestions on how to make sure this feed loop presents
> something close to 50 ohms?  Perhaps make it resonate with the last
> capacitor on the Pi network in the transmitter?
>
> Since I'm the ultimate lurker I don't know any local hams to help with the
> signal reporting - I'm trying to use the W5JGV argo viewer as a guide, but
> so far no hint of my signal there or on other posted images.  The HF rig 
> in
> the car can only hear my beacon for a few hundred yards.  I know it's a
> lousy receiver at LW, but it can hear the CBE NDB for about 20 miles, so
> even with the compromise antenna and lower power I think I should hear it 
> a
> mile or two if things were working.  I wish the W3EEE argo viewer was 
> still
> working since that was a lot closer to me.
>
> I can take this discussion off list if that is preferred, but like I 
> said -
> there may be others who have been lurking for a long time and need this 
> kind
> of info to dive in.  I've scoured the available online documents, but 
> there
> is a gap between very limited newbie info and the advanced fine-tuning 
> tips
> that assume you know what you are doing.  Maybe I'll take the lessons I
> learn and write a how-to guide.
>
> Thanks!
>
> Craig
>
>
>
> ----- Original Message ----- 
> From: <jrusgrove at comcast.net>
> To: <craig at wasson.com>
> Sent: Sunday, February 07, 2010 5:31 PM
> Subject: Re: [Lowfer] Beacon "IO" QSY to 185299.2
>
>
>> Craig
>>
>> What are you using for a final amplifier?
>>
>> If it is the 'standard' Class D totem pole like LEK and TAG have 
>> described
>> it will operate into a wide range of impedances. In that case there is no
>> need to ground the bottom of the loading coil to create an auto
>> transformer to match. Basically you let the antenna overall resistance 
>> end
>> up where it will and adjust the voltage to the final amplifier for 1 
>> watt.
>> You'll need a variable voltage regulated supply. As you bring the voltage
>> up the current will rise as well. Just stop when the voltage times the
>> current equals 1 watt. These finals are > 95% efficient so you can figure
>> your dc input power is essentially your rf output power.
>>
>> You'll almost certainly need a variometer to bring it to resonance. With 
>> a
>> typical Q of 300 or more you're not likely to hit resonance without an
>> adjustable element. RF current should probably be in the 100 - 150 mA
>> range. Don't worry about a clip lead rag tag setup at these frequencies -
>> you can clean it up once you get it working.
>>
>> Let me know if I can be of further help.
>>
>> Jay W1VD  WD2XNS  WE2XGR/2
>
> ______________________________________________________________
> Lowfer mailing list
> Home: http://mailman.qth.net/mailman/listinfo/lowfer
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Lowfer at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> 