Antenna Switch

[MUTNAV]

Just as an idea, if it's possible to separate the antennas vertically rather than horizontally, it may work out better. If you have access to an ARRL antenna handbook, they have charts that show how the vertical separation works. It would be under the repeater antenna section of the book.

I was just looking at an antenna handbook, and apparently the new ones don't have the section on "repeater antenna systems".

At 450 MHz, the book I have shows 30 feet of horizontal spacing gives about 40 Db isolation, vertically about 7 feet of spacing gives the same isolation...

The book however was addressing repeaters where the transmitter is just a few KHz from the receiver.

Your receiver of the radio not transmitting will end up (during the transmission) not being very useful for recepttion, so just don't plan on doing crossband repeat or high duty cycle things (transmitting almost continuously).

Thanks
Joel

 

[jazzboypro]

I was just looking at an antenna handbook, and apparently the new ones don't have the section on "repeater antenna systems".

At 450 MHz, the book I have shows 30 feet of horizontal spacing gives about 40 Db isolation, vertically about 7 feet of spacing gives the same isolation...

The book however was addressing repeaters where the transmitter is just a few KHz from the receiver.

Your receiver of the radio not transmitting will end up (during the transmission) not being very useful for recepttion, so just don't plan on doing crossband repeat or high duty cycle things (transmitting almost continuously).

Thanks
Joel

Thanks for the info. I have no plan for crossband repeat. Both radios would be used for different things one for DMR on UHF only and the other one for VHF FM Repeater work and D-Star VHF/UHF.

 

[jazzboypro]

If it's strictly a VHF radio only, and a UHF radio only, and they don't have "wide as a barn door filtering" like many of the ham radios with wide RX coverage do, then yes, it helps.

If it's dual band radios, then no, not necessarily, but can depend on the design.

An inexpensive watt meter that will read down to the 1/4 watt or less level and a 50Ω dummy load designed to handle the full output of your radio will be a good addition to your test equipment.
Obviously it'll let you check SWR.
You can attach the dummy load in place of the antenna and check transmitter output power.
You can attach the antenna/dummy load and see the interaction between the two antennas when transmitting.

If it's strictly a VHF radio only, and a UHF radio only, and they don't have "wide as a barn door filtering" like many of the ham radios with wide RX coverage do, then yes, it helps.

If it's dual band radios, then no, not necessarily, but can depend on the design.

An inexpensive watt meter that will read down to the 1/4 watt or less level and a 50Ω dummy load designed to handle the full output of your radio will be a good addition to your test equipment.
Obviously it'll let you check SWR.
You can attach the dummy load in place of the antenna and check transmitter output power.
You can attach the antenna/dummy load and see the interaction between the two antennas when transmitting.

I will have to look into a decent wattmeter/dummy load combo. I thought RigExpert were making wattmeters but it does not look like they do

 

[mmckenna]

I will have to look into a decent wattmeter/dummy load combo. I thought RigExpert were making wattmeters but it does not look like they do

There are good options.

If budget isn't a challenge, look for a used Bird 43. There's not much to them to break, so getting an old/slightly abused one won't be an issue. It's a line section, a cable and a meter. Easy to get replacement parts if there is something borked up inside.
Then you buy the slugs you need, based on frequency range and power level.

The nice thing about a Bird 43 is that it's something you can hand down to your kids, grand kids, great grand kids, probably another 50 generations beyond them. There are few things built as well as a Bird 43. I bet if you did a search on the phrase "Built like a brick outhouse" it would show a photo of a Bird 43.

They are in demand, but you can find good deals on line. I bought one probably 20 years ago, and it looked a little rough, but works just fine.

 

[RFI-EMI-GUY]

I have an Alpha Delta 4 way antenna switch in a box somewhere. If I recall it is strictly an antenna switch as opposed to a radio switch, and it grounds the unused ports. If this is so, it would be a bad thing to use and inadvertently transmit into a dead short.

 

[prcguy]

You might also look at the Telewave 44A wattmeter if most of your needs are VHF/UHF. It doesn't need any slugs and has 5W, 15W, 50W, 150W and 500W full scale settings. A Bird 43 is good and rated at 5% accuracy where the Telewave is rated 6% accuracy. I have 3 Bird 43s and 1 Telewave 44A and I seem to use the Telewave most of the time these days.

The Telewave is rated down to 20MHz and if you need something for HF/VHF/UHF a Bird 43 would be a better choice but the slugs will start to add up.

I will have to look into a decent wattmeter/dummy load combo. I thought RigExpert were making wattmeters but it does not look like they do

 

[mmckenna]

Good suggestion.

My "home" meter is a used/abused Bird 43.
The nice shiny new one I bought at work about 15 years ago was the Telewave 44a.
That and a 100 watt 50Ω load ride in the truck 24x7 while the fancy gear stays warm/dry in the office.

 

[jazzboypro]

There are good options.

If budget isn't a challenge, look for a used Bird 43. There's not much to them to break, so getting an old/slightly abused one won't be an issue. It's a line section, a cable and a meter. Easy to get replacement parts if there is something borked up inside.
Then you buy the slugs you need, based on frequency range and power level.

The nice thing about a Bird 43 is that it's something you can hand down to your kids, grand kids, great grand kids, probably another 50 generations beyond them. There are few things built as well as a Bird 43. I bet if you did a search on the phrase "Built like a brick outhouse" it would show a photo of a Bird 43.

They are in demand, but you can find good deals on line. I bought one probably 20 years ago, and it looked a little rough, but works just fine.

I will surely look for a used one and see what i can find

I have an Alpha Delta 4 way antenna switch in a box somewhere. If I recall it is strictly an antenna switch as opposed to a radio switch, and it grounds the unused ports. If this is so, it would be a bad thing to use and inadvertently transmit into a dead short.

I won't be using a switch. As a matter of fact, i will start by buying an adapter to connect my portable DMR radio to my external antenna and see what i see if there is enough activity to warrant another radio/antenna/feedline etc.

 

[Ubbe]

Those Bird43's are more for professional work, considering costs and the number of expensive slugs needed. You will need one slug for each frequency range and then double that amount to be able to handle both low power and mid power transmitters. We had lots of Bird43 at work but never took them to do field service. We used another light weigh meter that we throw in the tool bag that where much cheaper and had flip switches for 10/100W and forward/reverse and to calibrate. It where abused for 20 years without any issues. Even if it had a 10% accuracy it wouldn't matter, showing 45W instead of 50W.

I couldn't find it doing a picture search in Google but it covered both 70MHz VHF and 500MHz UHF.

/Ubbe

 

[jazzboypro]

Those Bird43's are more for professional work, considering costs and the number of expensive slugs needed. You will need one slug for each frequency range and then double that amount to be able to handle both low power and mid power transmitters. We had lots of Bird43 at work but never took them to do field service. We used another light weigh meter that we throw in the tool bag that where much cheaper and had flip switches for 10/100W and forward/reverse and to calibrate. It where abused for 20 years without any issues. Even if it had a 10% accuracy it wouldn't matter, showing 45W instead of 50W.

I couldn't find it doing a picture search in Google but it covered both 70MHz VHF and 500MHz UHF.

/Ubbe

I did some research and i arrived at the same conclusion. Very expensive for what i need to do and it's not a tool i will use very often. Even a used one become very expensive when you start buying the elements. I looked at some reviews and a few people claim that the 43 if far from being as precise as what the manufacturer claims. Most were recommending to avoid buying used elements also. I'd like to buy a wattmeter a some point but i don't think it will be a 43.

 

[mmckenna]

it's not a tool i will use very often. …... I'd like to buy a wattmeter a some point but i don't think it will be a 43.

That sounds like the correct answer.

No, they are not the right tool for the average hobbyists. They are a great tool for field service where they'll get exposed to a lot of abuse. The slugs are a challenge, but if you work on VHF and UHF systems only, it's not as much of a problem as some think.

The Telewave 44 that prcguy mentioned above, is a good compromise.

Or, find one of the ham radio oriented meters, those will work just fine for what you are doing.

 

[jazzboypro]

That sounds like the correct answer.

No, they are not the right tool for the average hobbyists. They are a great tool for field service where they'll get exposed to a lot of abuse. The slugs are a challenge, but if you work on VHF and UHF systems only, it's not as much of a problem as some think.

The Telewave 44 that prcguy mentioned above, is a good compromise.

Or, find one of the ham radio oriented meters, those will work just fine for what you are doing.

Unless i am not looking properly, the telewave 44A is over 1000$ US for a new unit and roughly around 500 for a used one.

 

[mmckenna]

I bought mine 12 or so years ago. I want to say I paid about $400 for it new.

 

[jazzboypro]

I bought mine 12 or so years ago. I want to say I paid about $400 for it new.

Looks like they are more expensive than that today. I'll keep looking

 

[AK9R]

A couple of suggestions for SWR/wattmeters:

Daiwa CN-501H, 1500 watts maximum, 1.8 through 150 MHz, $138 Daiwa Products CN-501H Daiwa CN-501H HF/VHF Bench Meters | DX Engineering
Daiwa CN-501V, 200 watts maximum, 140 through 525 MHz, $140 Daiwa Products CN-501V Daiwa 501 Series VHF/UHF Bench Meters | DX Engineering

I've used Daiwa meters in the past and have no complaints with them.

 

[jazzboypro]

A couple of suggestions for SWR/wattmeters:

Daiwa CN-501H, 1500 watts maximum, 1.8 through 150 MHz, $138 Daiwa Products CN-501H Daiwa CN-501H HF/VHF Bench Meters | DX Engineering
Daiwa CN-501V, 200 watts maximum, 140 through 525 MHz, $140 Daiwa Products CN-501V Daiwa 501 Series VHF/UHF Bench Meters | DX Engineering

I've used Daiwa meters in the past and have no complaints with them.

Thanks for the suggestions, it looks interesting. Do you know what is the smallest amount of power it will measure ? i don't see this information in the specs/user manual

 

[AK9R]

Looking at the HF meter, the smallest wattmeter range is 15 watts full scale. The stated accuracy is +/-10% of full scale.

 

[jazzboypro]

The goal here is to determine what power would be received by the non transmitting antennas when one of the 2 GP-3 is transmitting. It was my understanding that it should be in the 250mW range of less to avoid damaging the front end on the radios. It looks like the Daiwa can't measure such amount of power.