Topband: To clamp or NOT...that IS the question

[James Rodenkirch]

Oooops - sorta!!
Checked the schematic for the KD9SV pre-amp I have and find it does have clamping diodes at the input...DUH.....so, question/problem/concern resolved, in spite of myself!!  Hi Hi
Tnx to Don, WD8DSB, for querying me and suggesting I check my particular KD9V model!!
72/73, Jim Rpdenkirch K9JWV
P.S. WOW! HL5ILV was rockin' in to s/w UT this morning around 1250Z at 569 to 579, at times...I did work him but needed 50 watts to do it..NO QRP QSO with HL land today!  Also heard some STRONG JAs on 80 CW as well  Hope condx continue for the CQ 160 next weekend and hope to hear and work y'all with my QRP peanut whistle!

Date: Sat, 18 Jan 2014 13:53:01 -0500
Subject: Re: Topband: To clamp or NOT...that IS the question
From: wd8dsb at gmail.com
To: rodenkirch_llc at msn.com

Hi Jim,

You might post that info to the topband reflector (about your preamp having clamp diodes already included as part of the original KD9SV preamp design), as some guys were questioning what I was saying.  Even Gary KD9SV e-mailed me about my comment that the KD9SV preamp that you had might already have clamp diodes as part of the design and I reminded him that some of his preamp designs did indeed have diode clamps (1N914 diodes or equivalent) across the input to the electronics, and then he went and looked at some of his schematics and confirmed that I was indeed correct.


There are several different vintages/designs of the KD9SV preamp which causes some confusion to even the designer (Gary, KD9SV).

While I agree totally with what others have said about intermod as it relates to clamp diodes, I also believe in keeping systems as simple as possible.  The folks having the most negative feelings about clamp diodes also are the ones using RX antennas that have gains many magnitudes greater than what your RX antenna provides.


Just listen to what folks are saying and make the best decisions you can based on your own particular situation.

73,
Don (wd8dsb)



On Sat, Jan 18, 2014 at 12:53 PM, James Rodenkirch <rodenkirch_llc at msn.com> wrote:




Yup - Don../good observation and I checked thw schematic for the preamp and it has clamp diodes at the front end..


> Date: Sat, 18 Jan 2014 12:02:03 -0500

> From: wd8dsb at gmail.com
> To: w8ji at w8ji.com
> CC: topband at contesting.com

> Subject: Re: Topband: To clamp or NOT...that IS the question
> 
> Jim,
> 
> Getting directly back to your original question, I built a KD9SV preamp,
> and it has clamp diodes included in the design (I did not add them, they

> were part of the original design by KD9SV).  Does you KD9SV preamp already
> have clamp diodes protecting its input, and if so you have already answered
> your own question about adding clamp diodes to protect it (no reason to add

> them if you already have them).
> 
> If you go one step more and follow the advice that others have provided
> here, you might consider removing the clamp diodes (if you have them) based
> on their comments, but please understand that the gain of you RX antenna is

> approximately -36.3 dbi (based on the dimensions you told me), and it's
> very possible that you will not encounter the same kind of problems (using
> clamp diodes) as those using beverage RX antennas on 160 meters just due to

> the greatly reduced signal strength that your RX antenna provides compared
> with a full size beverage.
> 
> That's all I'm saying on this topic, over and out.
> 
> Don (wd8dsb)

> _________________
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