Date   

Re: Coax Probes into Waveguide

DougF VK4OE
 

Hello Andy and other readers.

An interesting project.....but I want to make sure that you're not presuming that a probe forming a waveguide-to-coaxial transition needs to be a quarter wavelength long - it's usually better not to be so.

Apart from off-the-shelf transitions made by the likes of Hewlett-Packard (e.g. X281A), the best-matched 'probes' that I have seen are not just straight 'rods' but they look more like inverted cones with the broad end in the middle of the waveguide.  And they're not a quarter wavelength long either.  I have done some trial-and-error experimentation and have confirmed that probes like these have worked very well in various projects.  I remember one case making a probe of increasing diameter using several pieces of brass tube of incrementally increasing diameter.  (Sorry, you can't work in waveguide and avoid some metalwork!)

And being a little shorter than a quarter wavelength, it is intuitively allowable for an adjustment screw to be introduced through the opposite wall, adding a little capacitance there.  But adjustment screws may need to be better placed at another location and the old trick of leading a small ball bearing around inside by way of a bar magnet held on the outside, is a great way to find where the 'sweet spot' actually is.

Approaching from another angle, a very good way of bringing any trial-end-error waveguide transition into submission is to have a close-fitting back short, the position of which is adjustable by sliding in and out a little.  Known good directional couplers (waveguide and/or coaxial) are your friends here!

Just a few comments to start.....

Cheers and 73,

--Doug Friend, VK4OE.


On 3/08/2016 20:12, Andy Talbot andy.g4jnt@... [ukmicrowaves] wrote:
 
Background first:
I'm taking a new look at the old G3JVL iris coupled filters in waveguide  as used in his transverter.  I have all the original design software, and a copy of MYJ where the design theory originally came from.   But I want to do it with a difference; in that the original used WG in and out, but I want SMA in/out

So, for a three cavity design, originally we had four irises;  two outer ones with large holes setting the Q or input/output transformation and two inner small irises defining the coupling, or K values.    I want to replace the outer irises by coax probes, so only two iris plates have to be installed, and the rest is drilling and tapping (about the only sort of metalwork I'm happy doing !)

So, how to design the probes for adjustable coupling.   Coax to WG transitions are a complete field in their own right, and there is no one correct answer; there are more variables than there are needed to do a complex match, so all sorts of responses can be produced.

However, for a filter, particularly a narrowband one, a  reduced coupling is going to be needed over that for a transition, so a shorter probe nearer to the backplane.   Which where it gets complicated if I don't want to make false starts in cutting metal and have to throw away bits of prepared and soldered guide.

IF I insert an SMA probe into the broad face of WG, I get a simple transition.  Now, the $24M question:  If I place a tuning screw on the opposite face of the WG so it would meet the probe, does anyone know how much it changes the coupling, or, indeed, in which direction.  Ie could I use a very short probe at a decent spacing from the backplane (say 20% of a wavelength) and rely on adjustment screws to get it right

Is there a better place for a coupling adjustment screw ?   

Or if I use an offset probe, not on the centreline of the broad face that will have reduced coupling, where then is the best place for a tuning screw ?

Anyone with experience in this area?

The  G3JVL transverter RF input filter, designed for 60MHz bandwidth, was originally targeted with a 28MHz IF in mind.  It would be nice to be able to do a 10GHz system that could feed directly into a high performance SDR radio without having to go via 144/43/1296 etc.   Even a 50MHz IF would suit many modern SDRs.

With just two iris plates to make and install instead of four, the JVL filter becomes an awful lot easier to build for those of us who aren't all that happy with metalwork

Andy  G4JNT


Re: Coax Probes into Waveguide

 

Hi Andy,
My inclination would be to put the probes in the centre of the cavity, and you will need only a very small insertion for bandwidth of the order of 1%. At least then you are coupling primarily to the intended mode in the waveguide, rather than higher modes which may produce unexpected results and add extra reactance.
It is advisable to maintain symmetry as much as possible. If the input and output couplings are the same and the two irises are the same and the three resonators are tuned, the filter has to work at the centre frequency, doesn't it. The bandwidth and the ripple may not be quite what you wanted, but you know the irises are right, being from a proven design, so you have only one thing to adjust, in/out coupling.
I made a dual mode cavity for 5.7GHz (with N connectors) The probes were 6mm diameter by 3mm insertion and bandwidth about 1%. That was square waveguide, yours will be rectangular, no doubt, and my intuition says that will increase the coupling somewhat. I would be tempted to start with something 3mm diameter and close to flush with the w/g wall. Easy to reduce the coupling with a shim under the connector flange.
73 es gl.

G3YKI


Re: wtd spare M57762

DougF VK4OE
 

Hi there Simon and other readers.

A couple of years ago I needed one and purchased the Icom equivalent at:

https://www.rfparts.com/module/550-1300-mhz/rfpower-551-1300-icom/sc1040.html

See how you go.....I still like those older bipolar modules....!

Cheers and 73,

--Doug Friend, VK4OE.


On 4/08/2016 17:21, gm4plm@... [ukmicrowaves] wrote:
 
local here looking to repair an amp

anyone got a spare M57762 ?

Even an unused amp with one will do

Cheers

Simon ZL4PLM


Re: Timepod (was - Morion OCXO)

dbztuzujdhgtrjzthxh
 

In addition to Grant comments, I'll add that TimeLab is not limited to working with the TimePod.
In fact TimeLab has been available for considerably longer than the Pod and works well with many other instruments.


Given the software is free, it's well worth a look.

ian


Re: wtd spare M57762

John Roberts <J.S.Roberts@...>
 

Simon,
I have one hardly used and mounted on a WDG017 board. The amp is in a milled box.
If your interested can you contact me directly at J.S.Roberts@...
Thanks
John G8FDJ

 
local here looking to repair an amp

anyone got a spare M57762 ?

Even an unused amp with one will do

Cheers

Simon ZL4PLM



Re: Timepod (was - Morion OCXO)

Christopher Bartram <cbartram@...>
 

Hello Derek

Many thanks for posting the link to the NIST paper. It made very interesting reading indeed, and I look forward to hearing of your results in time.

Vy 73

Chris
GW4DGU

--


wtd spare M57762

gm4plm@...
 

local here looking to repair an amp

anyone got a spare M57762 ?

Even an unused amp with one will do

Cheers

Simon ZL4PLM
zl4plm@...



Re: Has anyone bought one of these ...........

Mike
 

Hi

No because you have not provided the items name.

73’s

Mike g4wyz


Re: RSGB response to 5.6 GHz demolition

Mike Willis
 

Personally, I thought that while it was a good response, with many good points, it was a little too robust in the language used. This risks the detail in the argument being lost while the reader recovers from the initial hard punches.

Mike


Re: WG16

Christopher Bartram <cbartram@...>
 

Hello Adrian

I'll write this to the group, as it is of general interest.

LDF4-50 is not a particularly sensible choice of coax at 10GHz: I think the manufacturer rates it to about 8GHz. Counter-intuitively to many people's ideas, it's diameter is too large to use use reliably at that frequency. It can work very well, but it can also work as a very good attenuator, with an attenuation figure of 20+dB worse than might be expected. This is due to higher order wave propagation, where energy combines with the wanted signal propagated in the simple transverse mode either constructively or destructively: an effect which can be quite temperature dependent. I've been there, and spent a lot of time scratching my head before I realised what was happening

It's better to use a smaller diameter cable. I have a 5m length of LMR240 which works well at 12GHz carrying the LO signal to my 24GHz transverter, but it is probably not up to use as a low-loss antenna feed.

73

Chris
GW4DGU

--


Re: WG16

mike G6TRM
 


 
Hi Adrian,
I think you will find that flexible WG16 will not work as a rotator loop, It was not designed to be used for large continuous movement, but mostly to counteract vibration problems. The only way I know that truly works would be a rotatable joint from a large system 3cm marine radar, it will require to be on the rotational centre line of the mast, which will be another issue to be resolved. copper water pipe is a good alternative to WG16 but the rotating joint issues still remains..
 
good luck,
 
best regards,
 
mike G6TRM
 

----- Original Message -----
Sent: Tuesday, August 02, 2016 10:00 PM
Subject: [ukmicrowaves] WG16

 

Years ago I had various pieces of WG16 waveguide but over the yeas they have been given away!

Today i decided to try and feed my dish on the tower from the gable of the bungalow using a combination of WG16 and LDF 4 -50 ..This now gives me an external rotatable  antenna.....downside is that the loss in the coax overtakes the gain in the bigger dish.

I was amazed how little low  measured in the waveguide but equally disappointed in the nearly 3dB loss in

4M of coax.

So the question is where can I get Wg16 or other low loss alternative?  I have Contar rings and flanges


Adrian 


Re: Timepod (was - Morion OCXO)

Derek Kozel <derek.kozel@...>
 

The US National Institute of Standards and Technology has just published a paper doing oscillator metrology using Software Defined Radios. I have access to the same receivers as they used and will be replicating their setup, hopefully in the next month. I'll be sure to post my results and experiences to this list. The radios are considerably cheaper than the Timepod, compare well in the results, and can be used as transceivers for all the bands from 70 MHz to 6 GHz. I use it as the base for my microwave rigs.

https://arxiv.org/pdf/1605.03505v1.pdf

On Wed, Aug 3, 2016 at 11:12 AM, Andy Talbot andy.g4jnt@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

"Cross correlation" suggests  mixing of the two sources and averaging (filtering) the result followed by digitisation of the baseband output.   Or at least its equivalent using DSP    Quadrature mixer to resolve ambighities.

I've been intending to make something do that for ages- but its not high up the priority tree.

I've measured such reference sources by multiplying both the test signal and the reference  up to 2.5GHz, but 900Hz apart, then mixing the two signals and using a sound card to monitor the resulting 900Hz.   An FFT plot shows short term stabilities and frequency offsets.

'jnt


On 3 August 2016 at 18:29, Grant Hodgson grant@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

The Timepod is a very high performance instrument for measuring the
stability of signa lsources. It uses cross-correlation to reduce the
system noise floor to very low levels. It was designed by John Miles
KE5FX as a commercial product which is sold by Symmetricom.

Timelab is the analysis program that does the back-end processing,
also written by John and performs time, phase amd frequency analysis.

The Timepod uses LTC2216 ADCs and great care was taken with the signal
layout, use of low-noise regulators, signal conditioning etc. Digital
data is sent to the PC for processing in Timelab, which does the FFTs,
user displays etc.

Timepod retails for around $5k, out of the reach of most amateurs but
representing and exceptional price/performace for commercial
customers. The schematic is provided in the manual if you want to
roll your own!

regards
Grant G8UBN

Quoting "Andy Talbot andy.g4jnt@... [ukmicrowaves]"
<ukmicrowaves@...>:

> Interesting link - in a way. That 'TimePod', described as a 'Programmable
> Cross Spectrum Analyser' [whatever that is ] needed to provide input to
> the measurement software is an enigma. They state it uses "... high
> performance host-based DSP techniques ... " which really means everything
> that matters is done on the PC and the Pod could be something quite simple.
>
> My guess is, its a digitiser as in any direct sampling SDR (and judging by
> the upper frequency limit of 30MHz, an average-range one).
>
> 'jnt
>
>
> On 3 August 2016 at 08:54, Stephen Tompsett stephen@...
> [ukmicrowaves] <ukmicrowaves@...> wrote:
>
>>
>>
>> For comparing oscillators you might find Timelab useful
>>
>> http://www.ke5fx.com/timelab/readme.htm
>>
>> On 02/08/2016 19:29, Edward Harland g3vpf@... [ukmicrowaves]
>> wrote:
>>
>>
>> My MV89 came still attached to the PCB. Someone had gone round the edges
>> with tinsnips. No attempt had been made to de-solder the unit. It has full
>> output and works at all orientations.
>>
>> I tried comparing the frequency of the MV89 with the Leo Bodnar GPS and
>> found that for about an hour after both units were switched on the relative
>> frequency was changing pretty much continuously but then slowed and
>> stopped. After adjusting the frequency trimmer on the MV89 it held the
>> frequency for the next 30 minutes. Had to stop the test at that point. I
>> have no means of finding out which, or both, of the units were changing,
>> but the result looks very promising.
>>
>> Will now build a unit with built-in batteries so the MV89 is always on,
>> even when travelling to a /P location.
>>
>> Thanks for all the comments received - very helpful.
>>
>> Ed G3VPF
>>




on4kst keep getting <fsockopen connection refused >when sending spot

G8xvj@...
 

for the last two weeks I can't send any dx spots via on4kst it keeps coming up the this info

each time I try,<fsockopen connection refused> has one had this before.


Re: Has anyone bought one of these ...........

Neil Smith G4DBN
 

I bought one to see how it works. You need small fingers, but the thing does what is says on the tin. One output port is fixed frequency, selected on the top line, it has a seven-digit entry box and on-screen keypad for entry. The second output port is for the sweep function, there you set start, stop, step size and step period.  You can start and stop the sweep using two on-screen buttons.  It defaults to 100kHz step once a millisecond.  Top end frequency is 4.4GHz as it says. After a decent warmup, it was about 4.4kHz LF at 4.000000 GHz.

Not looked closely, but there is a setting for crystal frequency set at 30MHz, so it might be possible to inject a locking reference.  There is an unpopulated SMA socket location that could be for an external ref or maybe a VCO.  No sign of any documentation at all.

Looking at the noise, it seems to have rather noisy sidebands at -60dBc out to 100kHz, then it falls away fast to the noise floor of my 8562 at -80-ish.  Could be because I am using a USB power lead inverter thingy.  I'll get it on to a clean supply via the power socket instead and see how it compares.  It looks like it has a programming header, and there are four push buttons which do nothing obvious.

The harmonics at sub-GHz frequencies are terrible, it looks like it might be a square wave, with odd harmonics falling away only slowly, so it would need a serious LPF for anything requiring a pure tone.  Above 2GHz, it is much cleaner, and at 3.9GHz, the second harmonic was 60dB down and the third better than 80dB down. 
Output is about 0.5dBm at 200MHz and 2.4dBm at 2GHz, back down to 1.4dBm at 3.9GHz.
Spurs are about -70dBc

I only bought it to use as a signal source for 3.4GHz because my Agilent runs out of puff at 3GHz. Might find a few more uses for it, but it isn't going to replace the E4421B.  I might put it into a box, it is very convenient to use if it is running from a battery.
Neil G4DBN


Re: Timepod (was - Morion OCXO)

Andy G4JNT
 

"Cross correlation" suggests  mixing of the two sources and averaging (filtering) the result followed by digitisation of the baseband output.   Or at least its equivalent using DSP    Quadrature mixer to resolve ambighities.

I've been intending to make something do that for ages- but its not high up the priority tree.

I've measured such reference sources by multiplying both the test signal and the reference  up to 2.5GHz, but 900Hz apart, then mixing the two signals and using a sound card to monitor the resulting 900Hz.   An FFT plot shows short term stabilities and frequency offsets.

'jnt

On 3 August 2016 at 18:29, Grant Hodgson grant@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

The Timepod is a very high performance instrument for measuring the
stability of signa lsources. It uses cross-correlation to reduce the
system noise floor to very low levels. It was designed by John Miles
KE5FX as a commercial product which is sold by Symmetricom.

Timelab is the analysis program that does the back-end processing,
also written by John and performs time, phase amd frequency analysis.

The Timepod uses LTC2216 ADCs and great care was taken with the signal
layout, use of low-noise regulators, signal conditioning etc. Digital
data is sent to the PC for processing in Timelab, which does the FFTs,
user displays etc.

Timepod retails for around $5k, out of the reach of most amateurs but
representing and exceptional price/performace for commercial
customers. The schematic is provided in the manual if you want to
roll your own!

regards
Grant G8UBN

Quoting "Andy Talbot andy.g4jnt@... [ukmicrowaves]"
<ukmicrowaves@...>:

> Interesting link - in a way. That 'TimePod', described as a 'Programmable
> Cross Spectrum Analyser' [whatever that is ] needed to provide input to
> the measurement software is an enigma. They state it uses "... high
> performance host-based DSP techniques ... " which really means everything
> that matters is done on the PC and the Pod could be something quite simple.
>
> My guess is, its a digitiser as in any direct sampling SDR (and judging by
> the upper frequency limit of 30MHz, an average-range one).
>
> 'jnt
>
>
> On 3 August 2016 at 08:54, Stephen Tompsett stephen@...
> [ukmicrowaves] <ukmicrowaves@...> wrote:
>
>>
>>
>> For comparing oscillators you might find Timelab useful
>>
>> http://www.ke5fx.com/timelab/readme.htm
>>
>> On 02/08/2016 19:29, Edward Harland g3vpf@... [ukmicrowaves]
>> wrote:
>>
>>
>> My MV89 came still attached to the PCB. Someone had gone round the edges
>> with tinsnips. No attempt had been made to de-solder the unit. It has full
>> output and works at all orientations.
>>
>> I tried comparing the frequency of the MV89 with the Leo Bodnar GPS and
>> found that for about an hour after both units were switched on the relative
>> frequency was changing pretty much continuously but then slowed and
>> stopped. After adjusting the frequency trimmer on the MV89 it held the
>> frequency for the next 30 minutes. Had to stop the test at that point. I
>> have no means of finding out which, or both, of the units were changing,
>> but the result looks very promising.
>>
>> Will now build a unit with built-in batteries so the MV89 is always on,
>> even when travelling to a /P location.
>>
>> Thanks for all the comments received - very helpful.
>>
>> Ed G3VPF
>>



Re: WG16

mike G6TRM
 


Hi Adrian,
I think you will find that flexible WG16 will not work, It was not designed to be used for large continuous movement, but mostly to counteract vibration problems. The only way I know that truly works would be a rotatable joint from a large system 3cm marine radar, it will require to be on the rotational centre line of the mast, which will be another issue to be resolved. copper water pipe is a good alternative to WG16 but the rotating joint issues still remains..
 
good luck,
 
best regards,
 
Mike G6TRM
 
 

----- Original Message -----
Sent: Tuesday, August 02, 2016 10:00 PM
Subject: [ukmicrowaves] WG16

 

Years ago I had various pieces of WG16 waveguide but over the yeas they have been given away!

Today i decided to try and feed my dish on the tower from the gable of the bungalow using a combination of WG16 and LDF 4 -50 ..This now gives me an external rotatable  antenna.....downside is that the loss in the coax overtakes the gain in the bigger dish.

I was amazed how little low  measured in the waveguide but equally disappointed in the nearly 3dB loss in

4M of coax.

So the question is where can I get Wg16 or other low loss alternative?  I have Contar rings and flanges


Adrian 


Re: Timepod (was - Morion OCXO)

Grant Hodgson <grant@...>
 

The Timepod is a very high performance instrument for measuring the stability of signa lsources. It uses cross-correlation to reduce the system noise floor to very low levels. It was designed by John Miles KE5FX as a commercial product which is sold by Symmetricom.

Timelab is the analysis program that does the back-end processing, also written by John and performs time, phase amd frequency analysis.

The Timepod uses LTC2216 ADCs and great care was taken with the signal layout, use of low-noise regulators, signal conditioning etc. Digital data is sent to the PC for processing in Timelab, which does the FFTs, user displays etc.

Timepod retails for around $5k, out of the reach of most amateurs but representing and exceptional price/performace for commercial customers. The schematic is provided in the manual if you want to roll your own!

regards
Grant G8UBN

Quoting "Andy Talbot andy.g4jnt@... [ukmicrowaves]" <ukmicrowaves@...>:

Interesting link - in a way. That 'TimePod', described as a 'Programmable
Cross Spectrum Analyser' [whatever that is ] needed to provide input to
the measurement software is an enigma. They state it uses "... high
performance host-based DSP techniques ... " which really means everything
that matters is done on the PC and the Pod could be something quite simple.

My guess is, its a digitiser as in any direct sampling SDR (and judging by
the upper frequency limit of 30MHz, an average-range one).

'jnt


On 3 August 2016 at 08:54, Stephen Tompsett stephen@...
[ukmicrowaves] <ukmicrowaves@...> wrote:



For comparing oscillators you might find Timelab useful

http://www.ke5fx.com/timelab/readme.htm

On 02/08/2016 19:29, Edward Harland g3vpf@... [ukmicrowaves]
wrote:


My MV89 came still attached to the PCB. Someone had gone round the edges
with tinsnips. No attempt had been made to de-solder the unit. It has full
output and works at all orientations.

I tried comparing the frequency of the MV89 with the Leo Bodnar GPS and
found that for about an hour after both units were switched on the relative
frequency was changing pretty much continuously but then slowed and
stopped. After adjusting the frequency trimmer on the MV89 it held the
frequency for the next 30 minutes. Had to stop the test at that point. I
have no means of finding out which, or both, of the units were changing,
but the result looks very promising.

Will now build a unit with built-in batteries so the MV89 is always on,
even when travelling to a /P location.

Thanks for all the comments received - very helpful.

Ed G3VPF


Re: Morion OCXO

Stephen Tompsett
 

I'm using an HP53132 counter/timer to compare oscillators against a GPS locked rubidium reference, basically just measuring the phase difference between the oscillators under test. The software makes it easy to control the counter and acquire and analyse the collected data.

Stephen Tompsett


On 3 Aug 2016 13:41, "Andy Talbot andy.g4jnt@... [ukmicrowaves]" <ukmicrowaves@...> wrote:
 

Interesting link - in a way.   That 'TimePod', described as a 'Programmable Cross Spectrum Analyser'  [whatever that is ] needed to provide input to the measurement software is an enigma.  They state it uses  "... high performance host-based DSP techniques ... " which really means everything that matters is done on the PC and the Pod could be something quite simple.

My guess is, its a digitiser as in any direct sampling SDR (and judging by the upper frequency limit of 30MHz, an average-range one).

'jnt


On 3 August 2016 at 08:54, Stephen Tompsett stephen@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

For comparing oscillators you might find Timelab useful

http://www.ke5fx.com/timelab/readme.htm


On 02/08/2016 19:29, Edward Harland g3vpf@... [ukmicrowaves] wrote:
 
My MV89 came still attached to the PCB. Someone had gone round the edges with tinsnips. No attempt had been made to de-solder the unit. It has full output and works at all orientations.

I tried comparing the frequency of the MV89 with the Leo Bodnar GPS and found that for about an hour after both units were switched on the relative frequency was changing pretty much continuously but then slowed and stopped. After adjusting the frequency trimmer on the MV89 it held the frequency for the next 30 minutes. Had to stop the test at that point. I have no means of finding out which, or both, of the units were changing, but the result looks very promising.

Will now build a unit with built-in batteries so the MV89 is always on, even when travelling to a /P location.

Thanks for all the comments received - very helpful.

Ed G3VPF


On Tuesday, 2 August 2016, 12:45, "Michel Bourdon michel.m.bourdon@... [ukmicrowaves]" wrote:


 
you may also want to try the OCXO in various positions, i.e horizontal, vertical ...
I have one which only works when vertical !
73 Michel F6DZK

2016-08-02 12:55 GMT+02:00 eightgoes@... [ukmicrowaves] <ukmicrowaves@...>:
 
Some are low on output too. GM8BJF found you can gently heat the case and melt the solder seal and pull off the cover. This reveals a pcb which has a connection to the output pin. The SM output coupling C on this pcb can be replaced and the output level restored. I have done this to two of mine and successfully increased a very low output level. I suspect the C gets damaged on extraction from the original pcb....with a blowtorch!!?

73 de Chris G8BKE
 



--
Stephen Tompsett




Re: Coax Probes into Waveguide

Christopher Bartram <cbartram@...>
 

Hello Andy

My experience in that area is not too extensive, but I have been down a similar road to you, while designing my dual mode filter.

I had a good look at things that had previously been published, both professionally and in the amateur radio literature, and found very little to help. I suspect that a lot of information is available in company archives somewhere, but hasn't been published for commercial reasons. Certainly, I wasn't able to find any 'cookbook' design data from easily available sources

My approach was to use EM simulation to understand the whole of the filter. That allowed me to develop the loosely coupled transitions from 2.2mm coax to waveguide which were needed, without cutting metal. While the length of the probes, and their location along the guide were fixed, their penetration into the guide was a variable, allowing good RL to be obtained when the filters were set-up on my aged microwave net-an. I'll send the detail of the matching arrangement if you'd find it useful, but I don't think it would work without a lot of modification in your filter.

Once I finally retire, and have some time of my own, I'll write-up some of the microwave design work which I've done :-) My filter, of which I've made some 35 samples, was built from brass, managed 30MHz -3dB BW at 10368 with an insertion-loss of about 1.5dB at CF. There were no spurious responses below 10.37GHz, and the first spurious response above was at about 13.5GHz. And it didn't use irises!

Incidentally, I've used one of my prototypes as a dual resonator in a 'proof of principle' prototype of what I hope will be a very high performance VCO for 10GHz. The two cavities are effectively in series, so the phase slope of the resonator is extremely steep, resulting in a very high effective loaded Q. A low 1/f noise microwave amplifier is proving to be an 'interesting' exercise. More on that anon.

Vy 73

Chris
GW4DGU

--


Coax Probes into Waveguide

Andy G4JNT
 

Sent again as the original didn't appear...

On 3 August 2016 at 11:12, Andy Talbot <andy.g4jnt@...> wrote:
Background first:
I'm taking a new look at the old G3JVL iris coupled filters in waveguide  as used in his transverter.  I have all the original design software, and a copy of MYJ where the design theory originally came from.   But I want to do it with a difference; in that the original used WG in and out, but I want SMA in/out

So, for a three cavity design, originally we had four irises;  two outer ones with large holes setting the Q or input/output transformation and two inner small irises defining the coupling, or K values.    I want to replace the outer irises by coax probes, so only two iris plates have to be installed, and the rest is drilling and tapping (about the only sort of metalwork I'm happy doing !)

So, how to design the probes for adjustable coupling.   Coax to WG transitions are a complete field in their own right, and there is no one correct answer; there are more variables than there are needed to do a complex match, so all sorts of responses can be produced.

However, for a filter, particularly a narrowband one, a  reduced coupling is going to be needed over that for a transition, so a shorter probe nearer to the backplane.   Which where it gets complicated if I don't want to make false starts in cutting metal and have to throw away bits of prepared and soldered guide.

IF I insert an SMA probe into the broad face of WG, I get a simple transition.  Now, the $24M question:  If I place a tuning screw on the opposite face of the WG so it would meet the probe, does anyone know how much it changes the coupling, or, indeed, in which direction.  Ie could I use a very short probe at a decent spacing from the backplane (say 20% of a wavelength) and rely on adjustment screws to get it right

Is there a better place for a coupling adjustment screw ?   

Or if I use an offset probe, not on the centreline of the broad face that will have reduced coupling, where then is the best place for a tuning screw ?

Anyone with experience in this area?

The  G3JVL transverter RF input filter, designed for 60MHz bandwidth, was originally targeted with a 28MHz IF in mind.  It would be nice to be able to do a 10GHz system that could feed directly into a high performance SDR radio without having to go via 144/43/1296 etc.   Even a 50MHz IF would suit many modern SDRs.

With just two iris plates to make and install instead of four, the JVL filter becomes an awful lot easier to build for those of us who aren't all that happy with metalwork

Andy  G4JNT