[Elecraft] Dual Receiver Tricks

Tue Jun 25 22:51:57 EDT 2019

Some years ago when operating HF packet in S. FL., I built an antenna 
switching arrangement which would take the error signal from my PK-232, 
count the errors and at some point switch to the other antenna.   One 
antenna was an 80M inverted V, the other was a Butternut vertical 
mounted over a salt water tidal canal.  I generally found when the 
signal faded, thus more errors, on one antenna the signal was stronger 
on the other.   The system switched antennas during the receive cycle. 
    I also incorporated a power control system which looked at each 
packet acknowledgement and would reduce TX power a small amount.  After 
a number N of missed acknowledgements it would increase power in small 
amounts.    It was nice to have a radio which I could control power by 
applying a few volts to the ALC input.

The aluminum Butternut vertical over tidal salt water presented one 
issue, which was the SWR changed multiple times per day as the tide 
cycle rise and fall.  The SWR change wasn't a lot but clearly noticeable 
a 3' to 5' tide change.  In effect the ground moved up and down, 
regardless of the amount of copper buried in the canal bottom.   I guess 
that stuff is still there as we moved away and left it in the canal.   
Oh, the Butternut is now located in my shop,  clean and ready to install 
again.   It has only been there 23 years and I still plan to get around 
to it.........one of these days.

The things hams won't try and do.

73

Bob, K4TAX

On 6/25/2019 9:31 PM, Bill Johnson wrote:
> You are correct, I didn't acknowledge peak - null situations. I generally thought this was also done using antennas,  which was perhaps your point which I had no interest.
>
> Bill
> 920-421-1172
>
> ________________________________
> From: David Gilbert <xdavid at cis-broadband.com>
> Sent: Tuesday, June 25, 2019 8:36:44 PM
> To: Bill Johnson; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Dual Receiver Tricks
>
>
>
> Not sure what you are describing.  If you mean two antennas feeding two receivers at RF for diversity reception, yes ...  that works well but is not the same thing at all.  Your brain is doing some spatial processing, but it doesn't peak or null.  It also, as is apparent from the antennas you cite, compensates for polarization changes that would otherwise cause fading ... but it isn't peak/null.
>
> If instead you are talking about being able to adjust phase and adding or subtracting the result, that can be done at RF but it definitely requires additional hardware.  You can't get there with just the K3 or K4 as is.
>
> And none of what you describe would give you a numerical azimuth (or elevation) indication as the original post described.
>
> Dave   AB7E
>
>
> On 6/25/2019 6:19 PM, Bill Johnson wrote:
> Dave, the two receivers fed from two antennas give you what you are looking for at rf level.  It works super well.  On upper bands I have used SteppIR short vert with dipole.   My experience has been excellent vs single antenna.
>
> Bill
> 920-421-1172
>
> ________________________________
> From: elecraft-bounces at mailman.qth.net<mailto:elecraft-bounces at mailman.qth.net> <elecraft-bounces at mailman.qth.net><mailto:elecraft-bounces at mailman.qth.net> on behalf of David Gilbert <xdavid at cis-broadband.com><mailto:xdavid at cis-broadband.com>
> Sent: Tuesday, June 25, 2019 7:07:55 PM
> To: elecraft at mailman.qth.net<mailto:elecraft at mailman.qth.net>
> Subject: Re: [Elecraft] Dual Receiver Tricks
>
>
> Over the past few years I have twice requested Elecraft include
> something like that as a software modification, but nobody (either at
> Elecraft or here on the list) seems interested in the least. Since phase
> is preserved during down conversion in a superhet circuit the software
> crunching could even be done at audio ... it isn't required to be done
> at RF.  It doesn't require the K4 either ... the K3 and K3s with the new
> synths also make it feasible.
>
> In addition to simply determining signal direction, the software would
> potentially be able to equalize volume from the two receivers (generally
> required since typically two different antennas would be used) and then
> add or subtract the two signals to peak a desired signal or null an
> unwanted one.  The equalization could be done in software while the
> phase shifting would be manual and require a repurposing of a knob.  DX
> Engineering sells a stand alone unit for over $700 that performs these
> same functions at RF, while a software mod could do the same for free
> (to us ... obviously it would take a commitment of coding resources from
> Elecraft).
>
> Elecraft has already said that they would at some indeterminate time in
> the future consider sanctioning well-chosen and trusted third party
> software developers for ancillary applications for the K4, but I'd like
> to see this capability for my K3 as well.
>
> As an aside, it would theoretically be possible to investigate arrival
> angles using two horizontally polarized antennas placed one above the
> other a known distance apart.  At the least it might even allow a user
> to discriminate between two interfering signals from the same azimuth
> but arriving at different vertical angles.
>
> 73,
> Dave   AB7E
>
>
> On 6/25/2019 8:14 AM, Dick Dickinson wrote:
>> A late model SDR Receiver (only) is said to have a soon to be released
>> software update.  I've seen a demonstration whereby using 2 antennas and a
>> computer device, the unit will be able (to some degree?) determine signal
>> direction.
>>
>>
>>
>> Does Elecraft have plans to develop K4D software with such capabilities or
>> sanction 3rd party development of such?  Will there be other software /
>> firmware development to come with the K4D beyond that of a dual receiver
>> K3/s?
>>
>>
>>
>> Lastly, beyond control and perhaps IF output, will the K4 receiver(s) be
>> able to interface with external 'computers?'  (No, I'm not sure what I mean
>> by that!)
>>
>>
>>
>>
>>
>> Kindly,
>>
>> Dick - KA5KKT
>>
>>
>>
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