WG20 Round flange


Mark GM4ISM
 

Hi All
With a recent dramatic increase in activity and interest in GM for 24GHz, I have been improving my test set-up.
I have a nice WG20  variable attenuator, but unfortunately it has round  flanges, and I have only one  adaptor to square flange.
Has anyone out there got a spare WG20 round flange and ring set, or an adaptor to square flange that they would part with for a reasonable sum please?
Also I am short of SMA Coaxial attenuators, none of mine work well at 24GHz ( ie better than 20dB return loss). These are like hens teeth, but even one 6dB or 10 dB  quality unit would improve measurement accuracy dramatically.
I would consider swaps for these, there are some items I have in larger quantities than i need..  please ask!
 
Thanks
Mark
GM4ISM
 
 
 
 
 


g4bao
 

What!!!  Dramatic increase in 24GHz activity???

Can you send me details for the RacCom Column please?


73
John G4BAO


On 9 January 2015 at 15:47, gm4ism@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Hi All
With a recent dramatic increase in activity and interest in GM for 24GHz, I have been improving my test set-up.
I have a nice WG20  variable attenuator, but unfortunately it has round  flanges, and I have only one  adaptor to square flange.
Has anyone out there got a spare WG20 round flange and ring set, or an adaptor to square flange that they would part with for a reasonable sum please?
Also I am short of SMA Coaxial attenuators, none of mine work well at 24GHz ( ie better than 20dB return loss). These are like hens teeth, but even one 6dB or 10 dB  quality unit would improve measurement accuracy dramatically.
I would consider swaps for these, there are some items I have in larger quantities than i need..  please ask!
 
Thanks
Mark
GM4ISM
 
 
 
 
 



Alan
 

Hi John,

I will send you something quite soon....I have been running tests [getting a bit cold and wet of course]over a 74km path using an Endwave system with Brian GM8BJF - more tests to do but I think there will be around 6 GM stations possiblity qrv and 3 spare systems for folk that might be interested in going out /P.

73 Alan GM0USI/P




To: ukmicrowaves@...
From: ukmicrowaves@...
Date: Fri, 9 Jan 2015 16:37:04 +0000
Subject: Re: [ukmicrowaves] WG20 Round flange

 

What!!!  Dramatic increase in 24GHz activity???

Can you send me details for the RacCom Column please?


73
John G4BAO


On 9 January 2015 at 15:47, gm4ism@... [ukmicrowaves] <ukmicrowaves@...> wrote:
 

Hi All
With a recent dramatic increase in activity and interest in GM for 24GHz, I have been improving my test set-up.
I have a nice WG20  variable attenuator, but unfortunately it has round  flanges, and I have only one  adaptor to square flange.
Has anyone out there got a spare WG20 round flange and ring set, or an adaptor to square flange that they would part with for a reasonable sum please?
Also I am short of SMA Coaxial attenuators, none of mine work well at 24GHz ( ie better than 20dB return loss). These are like hens teeth, but even one 6dB or 10 dB  quality unit would improve measurement accuracy dramatically.
I would consider swaps for these, there are some items I have in larger quantities than i need..  please ask!
 
Thanks
Mark
GM4ISM
 
 
 
 
 




Christopher Bartram <cbartram@...>
 

Hello Mark

I've just checked, and I'm also short of round flanges - for my rather lovely Quasar variable attenuator amongst other things. I could also do with some square flanges and a couple of 26.5GHz rated SMA/3.5mm attenuators. If you do, by some chance, happen to come across a source I'd be grateful for the info.

I've been following Alan's adventures with 24, and it's good to see GM leading the way in encouraging activity on the band. I've been trying to work Brian for years on 24 from north Pembrokeshire when the 'HAM group have been at Gatehouse. Easy on 10GHz, but not on the higher band ...

Vy 73

Chris
GW4DGU


mw1fgq
 

Mark

Not a solution but a question for my own education:-

Would a length of suitable semi rigid cable make a useable dissipative attenuator at 24 GHz that could be reliably calibrated? I see that some of the smaller types are quoted with very high figures  of attenuation per 100ft (300-500 dB) and are rated well beyond 24G.

John

MW1FGQ




Mark GM4ISM
 

John,
Quite possibly, good enough for amateur purposes anyway.
I had not considered this. I have certainly measured moderate losses at 24GHz with such cable assemblies.
 
a few caveats
You will probably have to get the cable you use checked out on good testgear.  microwave round tables are good for this, (or a visit to my shack.. not too convenient from GW i guess)
I suspect the attenuation and match may be affected by bending the cable so once measured it should be left well alone.
Avoid Elbow connectors!
I am not sure if the impedance of such cables is always  50Ohms to a reasonable accuracy.  If you are buying new coax for this purpose you can choose cable and connectors to the appropriate spec.
 
I have no idea as to the absolute stability of this sort of cable over time, or over a temperature range but given the large numbers of these cables in use in microwave gear, I don't expect you will see much change when in use. Kept away from dampness, in the shack at a relatively constant temperature I would imagine this would be OK 
You should be able to dissipate a reasonable amount of power in these cables. With 50W of 10GHz into a length of  141 semi-rigid, the losses are sufficient that the cable runs quite warm (I estimate I am easily dissipating a 2-5 watts in the short cable between the TWT output and the waveguide transition in my PA
If the cable gets really hot the coax insulation expands and soldered SMA connectors fall off.  I have seen this several times.
 
I have just done a few measurements on some pre-made lengths I have around. The longest has 12 dB attenuation but is showing a ripple  ( 0.75dB peak to trough) on the sweep indicative of a slight mismatch in the measurement system. Measuring its match terminated in a precision load showed why, it had only 15dB return loss.
Shorter cables tested had return losses ranging from 15 to 22dB  (For what its worth the measurement set is calibrated and has a quoted 38dB directivity)
 
all told a good well terminated length of semi-rigid , calibrated using the average loss measured over the approx freq range you would not have a huge error. If you were using such a cable to drop the output to a level suitable for a power meter, the added uncertainty may well be acceptable, it is probably no worse than a surplus directional coupler or surplus attenuator. You should be able to make reasonably repeatable measurements, which with amateur equipment is about as good as you can hope for.  Even measuring the loss to a reasonable accuracy will require access to good test equipment in the first place.
 
Lastly, you simply cannot assume the cables and coaxial components you happily use at 10GHz will be good at 24GHz  Get everything checked and use only components you know work up that high.
 
 
 
 
  Regards
Mark
GM4ISM
 
 
 
 

Sent: Saturday, January 10, 2015 5:17 PM
Subject: [ukmicrowaves] Re: WG20 Round flange
 
 

Mark

Not a solution but a question for my own education:-

Would a length of suitable semi rigid cable make a useable dissipative attenuator at 24 GHz that could be reliably calibrated? I see that some of the smaller types are quoted with very high figures  of attenuation per 100ft (300-500 dB) and are rated well beyond 24G.

John

MW1FGQ

 

 

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Christopher Bartram <cbartram@...>
 

Hello John

The answer is that _if_ you can calibrate the length of transmission-line as an attenuator, eg. by using a stable, well matched source and a VSWR indicator like the HP415, and confirm that it's well matched, then it would make a perfectly usable, albeit frequency-dependent, attenuator. The phase response might be also be a problem in some applications ...

If you were starting from scratch, measuring the return-loss might be difficult problem to solve, as good coaxial components such as directional couplers at frequencies above 18GHz (where conventional SMA connectors run out of steam), are difficult or expensive to buy. Waveguide components are much easier to find, and work better than coaxial/planar ones at 24GHz and up.

Transmission-lines, such as a waveguide operating below its cut-off frequency, have been, and I think still are, used as attenuation standards, as it's possible to directly relate the physical dimensions to attenuation.



Vy 73

Chris
GW4DGU

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Brian Flynn GM8BJF
 

Chris,

I have a few round WG20 screw-up rings, no actual flanges for that type. I do however also have some WG20 round flanges with the tapped holes/captive screws. Can't remember their proper name. I can post if of interest.
I have tried to standardise on square flanges.

73s

Brian, GM8BJF.


mw1fgq
 

Mark and Chris

Thanks both for your informative replies, I may well make a start on my 24 Ghz system this year and will no doubt be back to ask more questions about it!


Whilst I'm on - has anyone made a PC soundcard based equivalent to an HP 415E or is there anything that can be suitably scaled for direct square law and VSWR indication? I guess that it might need an external amplifier and attenuator to match the spec, I already have a 415E and various elderly bits of gear that need it but it would be nice to have a big display for a demo.

Thanks

John

MW1FGQ



Martyn G3UKV
 

Hello John
There are at least 4 stations semi-local to you who would enjoy 24GHz tests at any time:
Namely G3UKV, G8UGL, GW4DGU and G4CBW. Also G3PHO a bit further over.
Also the UKmicrowavers 2015 calendar shows 24G contests for May 2/3, Jun 21, July 19, Aug 16, Sept 13, Oct 3-4 (along with 47G) - so there's lots of opportunities for a bit of action, and/or roving up there!
Also 2 active 24G beacons GB3MAN and GB3ZME if you find a suitable location.
73 Martyn G3UKV
 

On 15/01/2015 23:47, johnhowen@... [ukmicrowaves] wrote:
 

Mark and Chris

Thanks both for your informative replies, I may well make a start on my 24 Ghz system this year and will no doubt be back to ask more questions about it!


Whilst I'm on - has anyone made a PC soundcard based equivalent to an HP 415E or is there anything that can be suitably scaled for direct square law and VSWR indication? I guess that it might need an external amplifier and attenuator to match the spec, I already have a 415E and various elderly bits of gear that need it but it would be nice to have a big display for a demo.

Thanks

John

MW1FGQ




mw1fgq
 

Hi Martyn
Thanks for the encouragement, I'll do my best but the wheels grind exceedingly slowly around here, I'll definitely put 24 GHz on the list but it's dependent on work/money etc. I'll make a start soon.
Regards
John
MW1FGQ