[Lowfer] Lowfer transmitter testing

Pat Bunn pbunn at matrixei.com
Sun Aug 18 09:32:40 EDT 2013 

Jay

I expect it was my problem in using the antenna rather than a dummy.

I  copied your 4 get design pretty much exactly except I have a larger heat sink and chassis because the Antec heat sink was not available due to the fire that had. 

Looked at it this morning and it won't be hard to fix and I have plenty of fets. If you know of any surplus d loads let me know. I have a 300 watt one and a couple of smaller ones and a cantena that gets hot fast. I bought a couple of 600 watt 100 ohm Johansen strip resistors and may mount them on a big heat sink and see how that works. Newark had them on sale for about 27 bucks each. I have been looking for a better dummy load for a while.

I just wound 50 turns on a ft140-77 and will build a scope match today. Five 1000pf and a 390 of in parallel with two 220 in series works out to exactly 50:1 as a capacitive divider. Just need to cut some holes in a box.

BTW.  I am a Hammond Mfg distributor and they have come out with lots of new chassis sizes to pretty much duplicate the old Bud line. I can get Hammond items at much reduced pricing if you need anything.




Thanks again for your help.

Pat


Sent from my iPhone

On Aug 17, 2013, at 11:24 PM, <jrusgrove at comcast.net> wrote:

> Pat
> 
> You obviously need a bigger dummy load. Recall in a previous life putting a Heathkit Cantenna in a bathtub filled with cold water ... seemed to handle quite a bit of power ;~)
> 
> Yes, have a close look at the drains with the antenna attached. With the remote control motorized variometer here I've watched what happens to the drains as the antenna is tuned off resonance. One doesn't have to tune too far before things get 'hairy'. The ringing amplitude goes up fast with increased power.
> 
> Did you lose more than one FET? Usually just one makes the ultimate sacrifice and saves the others.
> 
> To answer your earlier question ... DK7FC run auto tuning on his their variometer. Unless you have a super high Q antenna (like DK7FC) it's not really necassary ... unless you want to remain on the air during an ice storm. Think W5JGV also runs one now that I think about it.
> 
> Jay
> 
> 
> 
> 
> ----- Original Message ----- From: "Pat Bunn" <pbunn at matrixei.com>
> To: "Discussion of the Lowfer (US, European, &amp; UK) and MedFer bands" <lowfer at mailman.qth.net>
> Sent: Saturday, August 17, 2013 11:04 PM
> Subject: Re: [Lowfer] Lowfer transmitter testing
> 
> 
>> Thanks Jay.
>> 
>> I did the initial testing with a dummy load at 300 watts with the variac turned down. I don't have a dummy load that can handle a continuous KW.
>> 
>> I'll replace the fets and try again with better monitoring of the drains. The drain voltages looked good at 300 watts with very little ringing. I didn't get a chance to look when I cranked up to 600 watts.
>> 
>> 
>> Pat
>> 
>> Sent from my iPhone
>> 
>> On Aug 17, 2013, at 10:46 PM, <jrusgrove at comcast.net> wrote:
>> 
>>>> Anyone remember way type core that you used. I have some ferrite type 43 and 77 large cores as well as some other stuff.
>>> 
>>> 77 material if you want to cover 137 kHz and 500 kHz.
>>> 
>>> Jay
>>> 
>>> 
>>> ----- Original Message ----- From: "Pat Bunn" <pbunn at matrixei.com>
>>> To: "Discussion of the Lowfer (US, European, &amp; UK) and MedFer bands" <lowfer at mailman.qth.net>
>>> Sent: Saturday, August 17, 2013 10:14 PM
>>> Subject: Re: [Lowfer] Lowfer transmitter testing
>>> 
>>> 
>>>> Thanks all. I may try to put on together tomorrow. Since I hope to run at 1KW I will use a capacitive divider. Anyone remember way type core that you used. I have some ferrite type 43 and 77 large cores as well as some other stuff.
>>>> 
>>>> Pat
>>>> 
>>>> Sent from my iPhone
>>>> 
>>>> On Aug 17, 2013, at 10:05 PM, Steve <VE7SL at shaw.ca> wrote:
>>>> 
>>>>>> whether due to wind whipping the antenna around or a bird landing on the loading wires - boy is that fun! <poof>
>>>>> 
>>>>> 
>>>>> I just love watching the scope match on a windy night...it's almost as if the antenna system is alive and breathing.
>>>>> 
>>>>> Steve
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> WEB - "The VE7SL Radio Notebook":  http://members.shaw.ca/ve7sl
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