[Drake] Roofing Filters

[Bob Camp]

Hi

Well it's only taken me about 40 years to figure out that louder is not 
necessarily better.

If you really want to do the pad thing right you need to rig up a pad 
both on the receiver input and on the receiver output. That's a bit 
more than most people are willing to do.

It is amazing just how little sensitivity you need in a radio when the 
lower HF bands are open. Lots of meters in an antenna times a couple of 
microvolts per meter can add up pretty darn fast.

It's also amazing how easy it is to talk yourself into a radio issue 
when the problem is something else entirely. I will freely admit to 
having spent a lot of time trying to fix a coax connector problem by 
troubleshooting a radio .....

Back a number of years ago I lived a couple of miles from a 50 KW AM 
station running at the top end of the broadcast band. I forget the 
exact frequency but it was about 1550 KHz.  I could actually get a watt 
or two on a Bird wattmeter off of my antenna if I matched it up at the 
low end of 160 meters. Lighting up a flash light bulb was a simple 
trick.

Needless to say overload was a bit of an issue. Any one of a number of 
radios had problems up through 40 meters and one even had problems on 
20 meters. I fretted about this for a number of months and tried 
various filters before I pretty much proved that a 20 db pad on the 
antenna took care of the problem. The pad didn't have much impact 
except to knock out the overload. I could still hear anything that was 
there.

Several months of home brew construction projects and the best solution 
turns out to be the little button on the front panel of the radio. Very 
embarrassing .....

	Enjoy!

		Bob Camp
		KB8TQ



On Aug 16, 2004, at 4:13 AM, Steve Thompson wrote:

> On Sunday 15 August 2004 19:05, Bob Camp wrote:
> snip
>>
>> Pop the antenna on the radio and make sure the noise out of the radio
>> goes up when you are tuned to a quiet part of the band you want to 
>> use.
>> Stick in a 10 db pad. Does the noise still go up? if so keep stepping
>> up the pad.
>>
>> Once you have a pad that keeps you from hearing antenna noise back off
>> by 10 db. Most of the time you will find that you have a 10 or 20 db
>> pad on the lower HF bands and a 10 db pad on 20 meters. Of course this
>> trick only works if the band is open....etc.
> Hurrah!!!! Well put, Bob.
>
> Unfortunately, it's a forlorn task trying to convince the average ham 
> that,
> often, a pad will improve their receive performance. I know so few who 
> really
> understand what makes a good receiver, and what limits it.
>
> Cheers,
>
> Steve
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