I just ran across something that is likely to make this situation a lot livelier. It might also end up with the amateur allocations being "sold" to broadcasters who suddenly need new frequencies.

Some scientists and NCAR, the National Center for Atmospheric Research, believe they have identified a feature that allows for more accurate prediction of sunspot cycles. And they do not agree at all with NASA. Their predictions for the cycle just starting is that it will be very high and possibly record breaking high.

New Sunspot Cycle Could Be One Of The Strongest On Record, New Research Predicts

Don't you just LOVE ambiguity? Place your bets now, will this cycle be big or little?

{^_^}    (No, I am not making book.)

On 20201205 09:35:11, Brendan Wahl wrote:

Hi Roger,

I've not seen much 'new' info for sometime now. The frequencies in use are the most recent datapoints, and since this is private industry, they seem to be good at keeping all else fairly private. What is yet to be found is the use of this outside of US>EU paths, say AS>US. Taking advantage of the markets on a 24 hour basis with a faster order transmission system would seem to be desirable for trading firms all over the world. Money from milliseconds.

Brendan WA7HL

Hi Roger,

I've not seen much 'new' info for sometime now. The frequencies in use are the most recent datapoints, and since this is private industry, they seem to be good at keeping all else fairly private. What is yet to be found is the use of this outside of US>EU paths, say AS>US. Taking advantage of the markets on a 24 hour basis with a faster order transmission system would seem to be desirable for trading firms all over the world. Money from milliseconds.

Brendan WA7HL

A big loop is probably best for RX performance, but has to be, well, BIG -  and robustly built.
The Maynard derivatives, especially the ultralight DX series (search uldx io-group)  perform impressively,
but are heavy and, needing many ferrite rods,  expensive to build.

You takes yer choice...

Michael 2E0IHW

On 06/12/2020 17:59, jdow wrote:

My working levels came from a DoD receiver specification that was lying around. Take two signals into the receiver front end and vary their identical levels upwards until the 3rd order IMD products were 1uv - if I recall correctly. The test signal level in dBm plus 107 dB is the dynamic range. They were looking for 80 dB. (None of that ARRL horse manure about the sum of the levels - each signal was -27 dBm with IMD products at -127 dBm. So I was testing around -20 dBm to -30 dBm.

(And nothing really beats physical size for antennas. And a simple loop can easily be large enough that you need a LOT of ferrite to get equivalent performance. HOWEVER, there is the detail that if the antenna is 0.1% efficient at MW a bigger antenna will generally not give you better performance.)

{^_^}

On 20201206 09:30:02, Mag loop Simon wrote:

Hi

In my honest opinion..

Ferrite antennas are really down on sensitivity compared to tuned mag loops. ( tried it.)

Useful for dfing..but no one uses them for low noise dx Rx antennas..there is a good reason for this ..

Ok if one builds a ferrite antenna from LOTS of bars then they can start to be of use..but y? When can do much better with a rx only multi turn loop. ( less cost more Q etc.)

Re varicap diodes for tuning..been done for years..problem now is finding suitable diodes..and really they make any difference to imds etc with the small voltages developed across loop, ( unless real close to AM broadcast station etc.)

Main issue with remote high Q loop antennas is tuning..this can easy be got around with stepper motor..

I have alot of experience with loop antennas..I use a LARGE one for 160m tx..

Simon g0zen 

A big loop is probably best for RX performance, but has to be, well, BIG -  and robustly built.
The Maynard derivatives, especially the ultralight DX series (search uldx io-group)  perform impressively,
but are heavy and, needing many ferrite rods,  expensive to build.

You takes yer choice...

Michael 2E0IHW

On 06/12/2020 17:59, jdow wrote:

My working levels came from a DoD receiver specification that was lying around. Take two signals into the receiver front end and vary their identical levels upwards until the 3rd order IMD products were 1uv - if I recall correctly. The test signal level in dBm plus 107 dB is the dynamic range. They were looking for 80 dB. (None of that ARRL horse manure about the sum of the levels - each signal was -27 dBm with IMD products at -127 dBm. So I was testing around -20 dBm to -30 dBm.

(And nothing really beats physical size for antennas. And a simple loop can easily be large enough that you need a LOT of ferrite to get equivalent performance. HOWEVER, there is the detail that if the antenna is 0.1% efficient at MW a bigger antenna will generally not give you better performance.)

{^_^}

On 20201206 09:30:02, Mag loop Simon wrote:

Hi

In my honest opinion..

Ferrite antennas are really down on sensitivity compared to tuned mag loops. ( tried it.)


Useful for dfing..but no one uses them for low noise dx Rx antennas..there is a good reason for this ..

Ok if one builds a ferrite antenna from LOTS of bars then they can start to be of use..but y? When can do much better with a rx only multi turn loop. ( less cost more Q etc.)


Re varicap diodes for tuning..been done for years..problem now is finding suitable diodes..and really they make any difference to imds etc with the small voltages developed across loop, ( unless real close to AM broadcast station etc.)

Main issue with remote high Q loop antennas is tuning..this can easy be got around with stepper motor..

I have alot of experience with loop antennas..I use a LARGE one for 160m tx..

Simon g0zen 

My working levels came from a DoD receiver specification that was lying around. Take two signals into the receiver front end and vary their identical levels upwards until the 3rd order IMD products were 1uv - if I recall correctly. The test signal level in dBm plus 107 dB is the dynamic range. They were looking for 80 dB. (None of that ARRL horse manure about the sum of the levels - each signal was -27 dBm with IMD products at -127 dBm. So I was testing around -20 dBm to -30 dBm.

(And nothing really beats physical size for antennas. And a simple loop can easily be large enough that you need a LOT of ferrite to get equivalent performance. HOWEVER, there is the detail that if the antenna is 0.1% efficient at MW a bigger antenna will generally not give you better performance.)

{^_^}

On 20201206 09:30:02, Mag loop Simon wrote:

Hi

In my honest opinion..

Ferrite antennas are really down on sensitivity compared to tuned mag loops. ( tried it.)


Useful for dfing..but no one uses them for low noise dx Rx antennas..there is a good reason for this ..

Ok if one builds a ferrite antenna from LOTS of bars then they can start to be of use..but y? When can do much better with a rx only multi turn loop. ( less cost more Q etc.)


Re varicap diodes for tuning..been done for years..problem now is finding suitable diodes..and really they make any difference to imds etc with the small voltages developed across loop, ( unless real close to AM broadcast station etc.)

Main issue with remote high Q loop antennas is tuning..this can easy be got around with stepper motor..

I have alot of experience with loop antennas..I use a LARGE one for 160m tx..

Simon g0zen 

Hi

In my honest opinion..

Ferrite antennas are really down on sensitivity compared to tuned mag loops. ( tried it.)


Useful for dfing..but no one uses them for low noise dx Rx antennas..there is a good reason for this ..

Ok if one builds a ferrite antenna from LOTS of bars then they can start to be of use..but y? When can do much better with a rx only multi turn loop. ( less cost more Q etc.)


Re varicap diodes for tuning..been done for years..problem now is finding suitable diodes..and really they make any difference to imds etc with the small voltages developed across loop, ( unless real close to AM broadcast station etc.)

Main issue with remote high Q loop antennas is tuning..this can easy be got around with stepper motor..

I have alot of experience with loop antennas..I use a LARGE one for 160m tx..

Simon g0zen 

Interesting, but do the advantages outweigh the disadvantages?

The fact that you’re tuning a specific signal with a significant degree of selectivity means that you’re unlikely to notice the effects of a strong out of band signal? If you do get problems you can null out the unwanted signal by turning the ferrite rod. The end result will be much the same as using a portable radio with its ferrite rod.

Would switching diodes used in some front ends have much the same problem?

 

I’ll do some experiments when I have time.

I suppose if the aerial coil is tuned to a really strong SSB signal the varicap voltage will swing a little and widen the tuning response curve?

 

Allan G3PIY

 

---

From: main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of jdow
Sent: 06 December 2020 12:49
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Build Experimental Loop for LF to HF.

 

How do you keep the varicap from causing all manner of IMD, some of it pretty exotic? Don't forget that the tuning voltage is "modulated" by the signal voltages in the tuned circuit.

{o.o}

On 20201206 02:19:50, Allan Isaacs wrote:

Hi Paul

Try a varicap and a ferrite rod.

A lot easier to handle and you do not need a ladder to adjust it when on top of a pole.

http://www.radiomuseum.co.uk/active.html

Allan G3PIY