Topics

432MHz ATU?


g4zod@btinternet.com
 

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD


ian hope (2E0IJH)
 

Yes MFJ make one, MFJ-924, but looks hard to get, https://www.hamradio.co.uk/accessories-aerial-tuning-units-mfj-aerial-tuning-units/mfj/mfj-924-antenna-tuner-w-wattmeter-pd-44.php
 
Ian
M5IJH

 
 
Sent: Monday, February 15, 2021 at 11:03 PM
From: "g4zod@... via groups.io" <g4zod@...>
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] 432MHz ATU?

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD


Mark GM4ISM
 

Julian

A 6:1 VSWR is about 3dB Return Loss. Think of it of this way, if your feeder has 1.5dB  loss (not unreasonable)

and you had no antenna at all, just an open cct, you would get 3dB Return Loss (feeder loss x 2)  I suspect that whatever is left of the connection to the yagi will not radiate that well... 

Whist matching that is theoretically possible, the  'good' match would likely  be very narrowband and  changing frequency may  make the mismatch worse, risking damage  anyway.

 If the mismatch changes in any way  the matching cct will make it worse,  risking damage.

 If you must use this  a 6dB power attenuator rated at the full TX power would add 12dB to the  return loss,  The rig will probably survive 15dB return loss 1.4:1 VSWR  That sort of attenuator is not common

You will hear and work even less but the rig would be reasonably safe

 Best option is to pop a dipole on a long fishing pole and use that as an antenna. It will probably work better than what is left of your MET

I do not recommend trying to use the MET antenna until it is fixed.

Mark GM4ISM



On 15/02/2021 23:03, g4zod@... via groups.io wrote:

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD


Virus-free. www.avg.com


Neil Smith G4DBN
 

If you can get hold of a VNA and see what the impedance looks like, you could make a two-stub tuner from coax. 6:1 sounds like the coax outer has corroded away or something, was the match ever OK, or has it always been off? Does it change across  the band? If so, what is the curve like?


A NanoVNA would illuminate the problem. Loads of examples of two-stub tuners out on the internet.

6:1 sounds like something disastrous though.


Neil G4DBN


On 15/02/2021 23:12, ian hope (2E0IJH) wrote:
 
Ian
M5IJH
 
 
Sent: Monday, February 15, 2021 at 11:03 PM
From: "g4zod@... via groups.io" <g4zod@...>
To: UKMicrowaves@groups.io
Subject: [UKMicrowaves] 432MHz ATU?

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD

_._,_._,_


Gordon REASON
 

Your club members are coming to do some work ...Thats ofk .

But do'nt gather for drinks and sarnies .


On 15 February 2021 at 23:03 "g4zod@... via groups.io" <g4zod@...> wrote:

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD


 


 


Robin Szemeti - G1YFG
 

I would have to agree with others,  with a 3dB return loss (6:1 VSWR) the chances are the aerial is no longer  connected and you just have feeder left.   1.5dB up,  1.5dB on the way back down and there you are.

You may do better to erect a temporary aerial, even a small 9ele beam on a bit of pole might be a significant improvement.



On Mon, 15 Feb 2021 at 23:44, Gordon REASON via groups.io <gordonj.reason=virgin.net@groups.io> wrote:

Your club members are coming to do some work ...Thats ofk .

But do'nt gather for drinks and sarnies .


On 15 February 2021 at 23:03 "g4zod@... via groups.io" <g4zod=btinternet.com@groups.io> wrote:

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD


 


 


--
Robin Szemeti - G1YFG


Mike Willis
 

ATU is a waste of time. Sounds like the coax connection is broken at the top. Enjoy 23cms and up until you can get it fixed.
--
Mike G0MJW


John E. Beech
 

Hi Julian,
I'm going to suggest you build a K4ERO turnstile out of wood & wire. Only 6dB gain, omnidirectional and
horizontally polarised. OK, what you hear will be several S points down on what you are used to hearing and vice versa
but you WILL be able to work stuff without damaging your rig.

de John G8SEQ

-------Original Message-------
From: Robin Szemeti - G1YFG <robin@redpoint.org.uk>
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 432MHz ATU?
Sent: Feb 16 '21 00:12

I would have to agree with others, with a 3dB return loss (6:1 VSWR)
the chances are the aerial is no longer connected and you just have
feeder left. 1.5dB up, 1.5dB on the way back down and there you are.

You may do better to erect a temporary aerial, even a small 9ele beam
on a bit of pole might be a significant improvement.

On Mon, 15 Feb 2021 at 23:44, Gordon REASON via groups.io
<gordonj.reason=virgin.net@groups.io> wrote:

> Your club members are coming to do some work ...Thats ofk .
>
> But do'nt gather for drinks and sarnies .
>
>> On 15 February 2021 at 23:03 "g4zod@btinternet.com via groups.io"
>> <g4zod=btinternet.com@groups.io> wrote:
>>
>> I have a long term problem with my 17 element MET Yagi. The VSWR
>> is rather high at about 6-1 and I cannot risk blowing my new
>> radio!
>>
>> I have no way of taking down my pump up mast to adjust the
>> matching on the antenna. The current restrictions mean I cannot
>> get my fellow club members around to help me drop the mast.
>>
>> As this means my activities on 432MHz have to be put on hold for
>> possibly many more months I need to find an interim solution. In
>> the mist and cobwebs of mind I recall an ATU for UHF frequencies.
>> I did a quick search and nothing came up.
>>
>> Can any group member confirm if an ATU for 432 MHz is practical
>> and if so any reference to one?
>>
>> Many thanks
>>
>> Julian G4ZOD
>
>>

--
Robin Szemeti - G1YFG