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midland portapak 77-805d low power out; midland portapak 77-805d low power out
Topic Started: Wednesday, 11. October 2017, 00:13 (276 Views)
ur5by9
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108 Charlie Tango 188

I have a midland portapak 77-805d UK

Used this a few times and found it to receive better than it seems to transmit.
I put this onto a power meter and its only doing a few watts out at 12V

I cant seem to find much information on this that helps me out.

Anyone have any experience with these as to which are the correct variables for output
This model seems to have some kind of tuning for the external antenna and I don't want to upset that
I'm just looking to get it back to 4w out
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pagan
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26 Charlie Tango 2069

Hi Chris....see the links below for the manual / specifications and a couple of videos showing how to "tweak" the transmitter & receiver. Don't forget to check that the switch (on the rear) is set to High power. I have one of these and it puts out just over 4 watts on high power according to my meter (using the telescopic antenna). If you use an external antenna the power readings may be different if the SWR changes.


Manual & Specs:

http://78roger.free.fr/midland/manuel/77-805(uk).pdf

Transmitter alignment:

https://www.youtube.com/watch?v=-k2ARbfEdbk

Receiver alignment:

https://www.youtube.com/watch?v=062Lt5V4cQs&t=2s
Edited by pagan, Wednesday, 11. October 2017, 02:09.
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ur5by9
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108 Charlie Tango 188

Hi Pagan :hi:

I seen those videos but the inside of my unit is very different from the one that is
on the bench being worked on.

The switch is on high power and its doing around 2.5watts high and a few hundred mw on low.
I'm using this straight into a dummy load power meter which is known to be fairly accurate.

It may have been set low from the factory or just over the years it needs a slight tweek to bring it back up to
its normal working power.

I could try to post a picture but since Photobucket has changed its policy I have yet to find a suitable replacement.

Any further advice would be with the greatest of thanks :)


I managed to find a picture which is the same inside but not my own picture.
If I can find another I will post more.

Posted Image

Another picture inside which I found on the forum

Posted Image

The thread is hear I wonder if this user is still active and could point me in the right direction.
Click for LINK
Edited by ur5by9, Wednesday, 11. October 2017, 12:54.
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Nik Gnashers
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26 Charlie Tango 573

My Midland Porta, only did about 2.5w out on high power, when using it's internal battery pack. When connected to a PSU it did 4w though.

Not sure what you are powering it with.
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ur5by9
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108 Charlie Tango 188

Hi and thanks for that info, I'm using the Midland from a variable power supply set at 12 Volts.
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Gunrunner
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ur5by9
Wednesday, 11. October 2017, 16:18
Hi and thanks for that info, I'm using the Midland from a variable power supply set at 12 Volts.

see what you mean but it may say 12v but its amps some of that type will do 12v but only put 3/4 amp and 2 amp out, but
they never put out 4amp or 5amp out that's why you are only getting 2w out and they hum and make strange noises to try it with a 5amp psu
and it will do 4w out hope this helps mate :cheers: :pirate:
Edited by Gunrunner, Wednesday, 11. October 2017, 17:56.
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pagan
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26 Charlie Tango 2069

Chris......I've just noticed that the manual (page 17...."Technical Specifications")...says that with a 12 volt supply the current drawn will be 250 milliamps (max) so the output will be 3 Watts. However, with a 13.8 volt supply it will draw a current of 300 milliamps (max) so that will give you 4 Watts. As Gunrunner said above, it's the amps (in combination with the voltage) that counts. Power = Voltage x Current.
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ur5by9
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108 Charlie Tango 188

Hi guys thanks for the info, The Psu is a 30 amp supply, I have tried it up at 13.8v and its close to the 3watts to be fair.

I still feel its a little low. Are we able to identify the output tuning cans so I can tweek this up slightly.

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Northern Crusader
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26 Charlie Tango 1760

The difference between 2.5W and 4W to the other end of the conversation is very slight but the difference in battery life can be quite significant.

Personally if it were me I'd leave it as it was, there is certainly very little if any real world benefit in upping it an extra watt or so and that basically any difference will only be observed on a power meter.

As for the "power=voltage x current", that isn't applicable other than measuring how many watts a radio draws and you certainly can not use it for working out how many watts a radio's PA will transmit other than for a rough guide, i.e "as a rule of thumb most 100W amateur radios will use around 23A on transmit at 100W".
Edited by Northern Crusader, Thursday, 12. October 2017, 11:22.
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ur5by9
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108 Charlie Tango 188

Fair comment I will leave it be.

Many thanks for the input.
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razor36
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q12 is the rf power
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