VK Logger Ham Radio Forum Archive

Nicely squeeezed in Peter!

Peter, are you switching those with a separate DC line up to the preamp box, or are you plucking 12V from up the antenna coax?

73 - Rob VK2GOM / GW0MOH

Rob,

I don't believe in running power up the coax - too many things can go wrong, when you are relying on an earth return through coaxial cable.

No there are separate switch lines for 1.2 and 2.4Ghz and another line for switching between the two bands (the SPDT relay under the voltage booster boards).

The default position is always preamps bypassed to ensure that no stray RF from one band can get into the other band.

DPDT Relays (right hand end) control the power to the voltage boosters and to the preamps.

So from the shack to the feed is just two cables, one the coax and the other a 7 core trailer cable with spare capacity if required.

Naturally sequencers control the whole process from the amplifiers down below.

Preamps are the W6PQL boards using the Avago ATF 54143 PHEMT

but I can also use the Minikits boards which use the MGF 1302 or later versions.

Cheers

Peter VK3QI

Attachments

Hi Peter, nice compact unit you've got there, well done!

A question about the 12v-24v boards, (and this may sounds stupid), how quickly do the 12v-24v boards 'power up' so to speak? I see sequencing timing in the 50-100ms range at times, so just wondering if these little boards take a certain amount of time to energise up to 24v and do/should you take this into account when you work out the timing etc?

VK1JA wrote:Hi Peter, nice compact unit you've got there, well done!

A question about the 12v-24v boards, (and this may sounds stupid), how quickly do the 12v-24v boards 'power up' so to speak? I see sequencing timing in the 50-100ms range at times, so just wondering if these little boards take a certain amount of time to energise up to 24v and do/should you take this into account when you work out the timing etc?

I have tested a couple of kinds, they were far too slow to switch the input in a time critical sequence (ie ms), power them continuously and switch the output.

If you are swithing relays in a failsafe configuration (relay operated for receive) you might get away with switching inputs, depending on how quidkly they release. Additional filtering some have suggested might extend that.

Owen

Jayson,

Owen is correct - in a time critical application it would be better to run the booster boards continuously and switch the output with a relay.

Typical relay switching times are 10 - 15 milliseconds.

However, with proper configuration of the sequencers this time can be accounted for in the whole switching scheme.

AS far as I can tell, the switching time of the power boosters (both on and off) is about the same time 10 - 15 millisecs - depends a lot on what voltage you have the output set to - the relays will operate properly and reliably between 20 and 30 volts.

As Owen says, if you add any filtering to the input or output of the booster boards, that will increase the switching time. At 1.2 and 2.4GHz there is no evidence of any noise from the booster boards, so no additional filtering is required.

Cheers

Peter VK3QI

VK3QI wrote:Owen is correct - in a time critical application it would be better to run the booster boards continuously and switch the output with a relay.

Another alternative to consider, something I do, and possibly the easiest...
Run the 12-28V DC-DC inverter all the time, as mentioned above, obviously wired to the hot side of the relay coils, and switch the GND side of the coil via an NPN transistor, as you might with any typical sequencing arrangement.

Thanks Peter, looking at your picture it wasn't clear as to how you had it set up. You wouldn't happen to have a block diagram for this set up would you? It'd be interesting to see - picture (err, block diagram) speaks a million words

By matter of interest, how does one measure the isolation and loss of relays? I've got a handful of unknown relays that it'd be nice to see how they perform.

My method is a little agricultural but it works for me.

Loss.
I use a power meter (or calibrated SWR meter) much like you do when measuring cable loss but do it at the highest frequency you have measuring (and signal generation) equipment, that way you can measure the small losses easier.
Terminate (50 ohm) all ports but the input. Put xcvr on input side with Power/SWR meter measure forward power and note reflected power also. Then put it downstream of the relay and measure. Watch that the SWR has not changed significantly. (I also make sure the same connectors are in line as the first measurement) What is the difference in power (I use 70cm or 23cm to conduct the test... ). The old power loss formula is easy to find on the net ... 10Log etc or simply use the following online tool (there are plenty of these online) http://www.sengpielaudio.com/calculator ... cation.htm .

Isolation.
Same signal in, measuring power on input side and a miliwat meter (100/1W selector on the power/swr meter only spans 20 db) or Specan (with appropreate attenuator to protect the specan from accidents) to measure the power spilling out the isolated (the one not sinking the power) port. Don't forget to terminate the active output. Check with failsafe state then (changing connections on the output) with relay activated. Isolation should be the same on both ports but not always so. Calculate using power loss formulae or convert levels to DBm and use subtraction.

ZL2BKC wrote:I have since purchased 2 High Gain Telecom relays and have found them to be 100% identical to the ACE Technologies relays ...

VK4EDD wrote:... Thinking of the High Gain Technology ones like http://www.ebay.com.au/itm/301014854971 ... 1423.l2649.

I bought two and they arrived at my door via registered post in just 6 days. They look great and measure OK with an ohm meter. While they are not labelled "Opt: Non." like the black ones, they do connect as per Wayne's diagram in a similar thread at viewtopic.php?f=40&t=11101 (i.e. no connection from J1 to J3 in the normally open condition).

Question is: The claimed power rating is 300W at 1GHz ... does anyone know what they would handle at 144 or 432 MHz? (Google wasn't my friend).

73,

ZL1RS wrote: I bought two and they arrived at my door via registered post in just 6 days. They look great and measure OK with an ohm meter. While they are not labelled "Opt: Non." like the black ones, they do connect as per Wayne's diagram in a similar thread at viewtopic.php?f=40&t=11101 (i.e. no connection from J1 to J3 in the normally open condition).

Question is: The claimed power rating is 300W at 1GHz ... does anyone know what they would handle at 144 or 432 MHz? (Google wasn't my friend).

73,

I don't think there is any referencible material for the origial relay being rated for 300W - I am not sure where that number came from. Likewise for other ferquencies

Taking a scientific approach it is the loss and dieletric breakdown which governs the power limiting factors within the specified temerature range. Industry 70deg C and 125 deg C are a little extreeme for operating conditions as a relay is not normally subjected to high termeratures, unless the fan fails in your 1KW PA so in a controlled environment you could go higher.

The spec for another relay shows a power rating graph on page 6 which is a useful guideline for most relays:
http://www.teledynecoax.com/pdf/coaxial ... TCHING.pdf

Based on the low loss and use of silver plating I would rate this as an high power relay for the curves in the attached reference.

From the reference it can be infured from the 300W rating at 2.2GHz you can safely run 800W at 70cm and 1.5KW on 2m. I would not go beyond this power level for lower ferquencies for 2 reasons (1) it is not leagal to do so, and (2) Dielectric breakdown starts to become an issue.

It is often forgotten that loss increases with higher SWR, so be careful to ensure you use the relay in a 50 ohm environment.

--
Wayne

ZL1RS wrote:...
Question is: The claimed power rating is 300W at 1GHz ... does anyone know what they would handle at 144 or 432 MHz? (Google wasn't my friend).

I don't know the answer to your specific question, but the following might provide a way forward.

If you can find manufacturers specs, use them... otherwise...

Insertion Loss of coax relays tends to be proportional to frequency up to some point where it then degrades quite quickly. You will usually try to use them below that knee so the assumption of Insertion Loss proportional to frequency is not a real bad guess.

Now Insertion Loss does not imply conversion of the corresponding amount of energy to heat, it also includes the effect of mismatch... but again, in a region where the Insertion VSWR is very low, Transmission Loss (RF energy converted to heat) is approximately equal to Insertion Loss.

Taking those principles, then in the region below the knee of the Insertion Loss characteristic, and given that mostly these relays are limited by heat generated in the contact area, maximum power will be close to inversely proportional to frequency... ie one third the frequency, three times the power.

The coax connector will cap power, if you are using SMA, you won't realistically get 3kW power rating at low frequencies! For this reason, relays with N connectors will tend to be capped at 1kW or so.

Operating at VSWR S reduces power handling due to heating effect by a factor of 1/S... so a 1000W relay operated with VSWR=2 is good for 500W.

Because the heat mechanism has considerable latency, low duty cycle usually allows higher PEP.

Owen

VK4EDD wrote: Thinking of the High Gain Technology ones like http://www.ebay.com.au/itm/301014854971 ... 1423.l2649.

As I am using this relay with a LNA, would I need two of these? They have 4 connector slots so was just curious if I could get away with just one of these. If this is the case than I have just saved some money

Eddie

Eddie

You should need only one of these relays. They work as in the following 'schematic' I've just drawn. I've just received two more.... but probably should've got another three of four by the time I finish all of the projects! Good luck,

...and 2 ordered by me as well!

Thanks Scott,

Have just ordered one, should take about 2wks. When it gets in I might have to make contact so I know what way is what.

Eddie

ZL2BKC wrote:... The spec for another relay shows a power rating graph on page 6 which is a useful guideline for most relays:
http://www.teledynecoax.com/pdf/coaxial ... TCHING.pdf

Based on the low loss and use of silver plating I would rate this as an high power relay for the curves in the attached reference. ...

Thanks Wayne and others for your comments. I have used and abused coax relays similar to the teledyne ones ... they seem to survive at 800W on 2m, and at 1kW on 6m if not hot switched. Hot switching them will burn the contacts in a flash (excuse the pun!)

When one finally let the smoke out (a lapse of concentration when tired) I opened it up and was surprised at the VERY flimsy construction ... the fixed contacts on the ends of the N-type connectors were only about 2mm in diameter and the 'blade' about 3mm wide and less than 1mm thick, but by comparison with the center pin in an N-type connector one could see it should survive (if not hot switched). Hot switching will generate a spark much like an arc welder that will eat the 'blade' away just like a welding rod!

Fortunately I had 9 more and they only cost $10 each, so it wasn't a big problem ... even so I changed the relays in the 6m amplifier for vacuum relays with a speed up circuit to ensure they were changing faster than the rig could generate RF and so prevent another hot switch occurrence (sequencing was not an option in that system).

I'll try one of the black 'Telecom' relays on my 800W 2m tube amplifier and see how it goes. That PA will survive if the relay gives out ... I think there are plenty of people here with stories about LDMOS amplifiers that wouldn't

73,

ZL2BKC wrote:...
The spec for another relay shows a power rating graph on page 6 which is a useful guideline for most relays:
http://www.teledynecoax.com/pdf/coaxial ... TCHING.pdf
...

Interesting, these have negative Insertion Loss. Amplifiers have negative insertion loss, attenuators have positive Insertion Loss.

Owen