Topband: Low dipole for receiving

[Brian_ve7jkz]

I wonder too if it's worth the effort, Grant, OTOH there's not much to 
lose for a few hours work to install and then try out. I've tried 
various loops and things over the years and the BC band filter from the 
1996 ARRL Handbook - and probably later - does an excellent job. I've 
used my N2PK analyzer to sweep it and it is indeed 60dB attenuation 
across the BC band, better in some places. Playing around with some of 
the softrock radios where the BC station really killed 'em a 690Khz 
notch filter did a good job as well.

Brian VE7JKZ


On 9/17/2013 10:39 PM, Grant Saviers wrote:
> Not an expert by any means, but I wonder if it is worth the effort to 
> match the antenna to the feedline?  Local and band noise and your NVIS 
> pattern say to me that gain isn't a problem,  then there is the YIKES! 
> of 50kw so close, so you need a killer HP filter. Have you tried one? 
>   I had plenty of rf from a 50kw station 1 mile away line of sight to 
> my 80m vertical, and yes my dipole at 60' was quieter, but still 
> needed a HP filter.  1 volt of 1MHz BC signal on my power lines and 
> good line filters were needed also.
>
> Here is a nice article on receive transformers which can help plan a 
> step up design.
> http://www.dxing.info/equipment/impedance_matching_bryant.pdf
>
> OTOH, I have a DX eng receive only 4sq, 70' on a side, no BC problems 
> at a new QTH, no radials and it works quite well on 160/80.  Not 
> cheap, but effective and might fit on your lot.
>
> Grant KZ1W
>
>
> On 9/17/2013 8:38 PM, Brian_ve7jkz wrote:
>>
>> I've been looking at a very low dipole to hopefully assist in 
>> receiving. Living in suburbia space is limited but thanks to a 
>> helpful neighbor I could put up something in the shape of an L. I 
>> would have a 90ft straight length, then the feedpoint, then a 30ft 
>> straight length, a 90 degree turn, followed by another 60 ft straight 
>> length. Total length of 180ft approx. Running along the top of the 
>> garden fence approx 6ft high.
>>
>> EZNEC 3 tells me that at 1.83Mhz the feedpoint impedance would be 
>> 0.65-j590, and at 3.52Mhz it would be 1.7+j510. How do I match it? I 
>> could always use a relay to switch in some L for 160m and some C for 
>> 80m, then a transformer to get to close to 50 ohms, then a high pass 
>> filter because I'm only a few hundred yards from a 50kW BC station on 
>> 690Khz, followed by a W7IUV amplifier.
>>
>> Is this a reasonable approach or is there a better/simpler way?
>>
>> Brian VE7JKZ
>>
>>
>>
>>
>> _________________
>> Topband Reflector
>>
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