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Deshibo GA-450 Loop Antenna Modification Question

 

Hi all,
?
I have been reading with lots of interest the post by AA7U Steve on his findings and modification experiments
with his GA-450.?
?
Steve, did you find that after doing the modification to power the RF board directly with 12 volts DC, that there
was less noise generally, or was that only in this particularly troublesome MW to 3MHz section?
?
I have been having fun experimenting with my as yet unmodified GA-450 and, providing I turn my radio's gain
way down low, have been rather impressed with the results. It's an improvement over the telescopic whip and it's nice to be able to have some directivity.?
?
However, the gain is rather excessive in my opinion and I wonder if anyone has any ideas how that might be reduced......? I have no experience with varactor-tuned loops, but have buils lots of other types, and my latest activie antenna for MW and HF can have the gain adjusted by reducing the voltage to the AMP. I'm guessing a similar arrangement will not have quite different results with the varactor set-up and just lower the maximum tuned frequency........
?
The photos you have posted in the files section Steve will be invaluable if I decide to do any modifications.?
?
But it would be sad to lose it's portability.
?
Anyway, hope someone can offer a little bit of advice! Thanks. Adam (M6RDP
 

The general construction is a problem, in addition to trying to get a high impedance tuned loop to operate effectively within a few inches a DC-DC convertor.
?
I suspect that screening some of the leads and using a metal enclosure for the control box would be beneficial.
?
I've previously made a similar sized passive tuned loop, and that actually worked pretty well, although the need to retune it every time you change frequency is not so good, its small size makes it very handy for interference hunting. I did offer the design to a well known company, but they also concluded that the need for tuning was not going to appeal to their main customer base.
?
Regards,
?
Martin
?
On Sat, Feb 1, 2025 at 10:35 AM, Adam wrote:

did you find that after doing the modification to power the RF board directly with 12 volts DC, that there
was less noise generally, or was that only in this particularly troublesome MW to 3MHz section?
 

Hi Martin
?
Good to hear from you and thanks for the reply. I agree about the shielding from the DC converter and if I had the skills I may possibly try to attempt it myself. Another alternative is to look out for another used one at a very good price to experiment with modifying, keeping this one intact. I have to say my expectations were very low and I was expecting it just to be awfully noisy and pretty much unusable but I have been pleasantly surprised. Interesting about the tuned loop story. With so much RFI around I would have thought that was a bad decision on their behalf. I thought us radio enthusiasts loved nothing better than a bit of tinkering with electronic equipment! Although my friend at the radio club jokedthat we don't call it "tinkering" we call it "technical assessment"!!
73 Adam?
?
?
 

Just a couple of ideas:

SHIELDING:? It's not a perfect shielding material, but will illustrate if good shielding would improve things.? At any hardware store, you can buy wide "decorative" shiney aluminum tape.? While the adhesive is not conductive, if you overlap enough, there will be enough capacitive coupling between applications to enable a "reasonable" degree of shielding.? It's inexpensive and at least worth a try.?

BEST CASE:? Get rid of that switcher!!!? In the design of the overall antenna, there should have been absolutely no excuse to install a switcher that close to the receiving element - the loop.? That amounts to engineering WORST PRACTICES!!!? Build yourself a good linear supply with a transformer (surplus), a bridge rectifier (surplus), filter capacitor (surplus), and a 3-terminal regulator (surplus).? You could even build it into the existing plastic enclosure.

Dave - W?LEV


On Sat, Feb 1, 2025 at 6:31?PM Adam via <adamtoynton=[email protected]> wrote:
Hi Martin
?
Good to hear from you and thanks for the reply. I agree about the shielding from the DC converter and if I had the skills I may possibly try to attempt it myself. Another alternative is to look out for another used one at a very good price to experiment with modifying, keeping this one intact. I have to say my expectations were very low and I was expecting it just to be awfully noisy and pretty much unusable but I have been pleasantly surprised. Interesting about the tuned loop story. With so much RFI around I would have thought that was a bad decision on their behalf. I thought us radio enthusiasts loved nothing better than a bit of tinkering with electronic equipment! Although my friend at the radio club jokedthat we don't call it "tinkering" we call it "technical assessment"!!
73 Adam?
?
?



--
Dave - W?LEV
 

Hi Dave W0LEV
?
Thanks I didn't get a notification of your reply but just checked in and saw it and appreciate your time and comments especially regarding the aluminium tape which I have no experience of and would like to try.
?
Mr Everythingia (think I've got that YouTube name correct) did as you suggested and completely bypassed the DC converter. Surprisingly though he found a USB powered 9V battery performed admirably, with all the RFI gone.
?
I've pried off the bottom of the loop control box which came off fairly easily with mobile phone tools. Do you or does anyone else know if these are JST PH connectors?
?
?
It's so I'll buy a pack and try the 9V battery thing and might report back here my findings in case anyone is interested.
73 Adam?
 

Hi Adam,
?
The retaining clip looks slightly different.
?
These could be a match, but without measuring them I can't be certain.
?
?
Regards,
?
Martin.
?
On Tue, Feb 4, 2025 at 06:52 PM, Adam wrote:

Do you or does anyone else know if these are JST PH connectors?
 

Yes, these are very common connectors I see all the time.?

A standard 9-VDC "transistor" battery will supply roughly 400 to 500 (not the Chinese knockoffs) mAH of energy.? With that and knowing the current draw of your preamp, you can determine how long the 9-volter will last.

Dave - W?LEV


On Tue, Feb 4, 2025 at 6:52?PM Adam via <adamtoynton=[email protected]> wrote:
Hi Dave W0LEV
?
Thanks I didn't get a notification of your reply but just checked in and saw it and appreciate your time and comments especially regarding the aluminium tape which I have no experience of and would like to try.
?
Mr Everythingia (think I've got that YouTube name correct) did as you suggested and completely bypassed the DC converter. Surprisingly though he found a USB powered 9V battery performed admirably, with all the RFI gone.
?
I've pried off the bottom of the loop control box which came off fairly easily with mobile phone tools. Do you or does anyone else know if these are JST PH connectors?
?
?
It's so I'll buy a pack and try the 9V battery thing and might report back here my findings in case anyone is interested.
73 Adam?



--
Dave - W?LEV

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